Lanthanide-doped Sr2ScF7 nanocrystals: controllable hydrothermal synthesis, the growth mechanism and tunable up/down conversion luminescence properties

Article abstract of DOI:10.1039/c6tc05477c

Sr₂ScF₇:Ln³⁺ (Ln = Ce, Tb, Eu, Sm, Dy, Er, Tm, Ho and Yb) nanocrystals were firstly synthesized via a one-step hydrothermal route without employing any surfactants. The shape and size of the Sr₂ScF₇ nanocrystals could be readily tuned from nanorods with 120 nm length and 50 nm width to nanoparticles with a uniform diameter of 15 nm by doping 30% Ln³⁺ with a larger ionic radius. Furthermore, the influence of pH values, F^? sources and different surfactants on the sizes and morphologies (including nanorods, quadrangular microplates, cubes and polyhedrons) of the as-prepared products was systematically investigated and the possible formation mechanism for the products has been proposed. The XRD, SEM, EDS, PL analysis and decay lifetimes were used to characterize the products. For DC photoluminescence, the Sr₂ScF₇:Ln³⁺ nanocrystals show the characteristic f-f transitions with emission colors of bluish violet (Ce³⁺, Tm³⁺), green (Tb³⁺, Er³⁺, Ho³⁺), blue (Dy³⁺) and orange (Eu³⁺, Sm³⁺) respectively. Under single wavelength 980 nm excitation, the blue UC emissions of Sr₂ScF₇:Yb³⁺,Tm³⁺ nanocrystals at 474 nm due to the ¹G₄ → ³H₆ transition of Tm³⁺, the green UC emissions of Sr₂ScF₇:Er³⁺ nanocrystals at 522/544 nm assigned to the ²H_11/2 → ⁴I_15/2/⁴S_3/2 → ⁴I_15/2 transitions and the red UC emissions of Sr₂ScF₇:Yb³⁺,Er³⁺ at 660 nm from ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ were observed. Based on the generation of red, green, and blue emissions, the Sr₂ScF₇:Yb³⁺,Er³⁺,Tm³⁺ nanocrystals could produce multicolor, particularly in the white region (0.320, 0.330) by controlling the doping concentration of Tm³⁺ in the Sr₂ScF₇:Yb³⁺,Er³⁺,Tm³⁺ nanocrystals. Controlling the doping concentration of Tm³⁺ is an effective way of modulating the luminescence properties of Sr₂ScF₇:Ln³⁺ by controlling its size and morphology. The as-synthesized phosphors might be potentially applied in the fields of color displays, light, photonics and biological imaging.

Full text of DOI:10.1039/c6tc05477c

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DOI: 10.1039/C6TC05477C
Journal Name
ARTICLE
Lanthanide-doped Sr ScF nanocrystals: controllable
2
7
hydrothermal synthesis, growing mechanism and tunable
up/down conversion luminescence properties
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
b
c
DOI: 10.1039/x0xx00000x
Bei Zhao, Jun Yang,* Dingyi Shen, Shanshan Hu, Xianju Zhou and Jianfeng Tang
3+
www.rsc.org/
Sr
2
ScF
7
:Ln (Ln = Ce, Tb, Eu, Sm, Dy, Er, Tm, Ho and Yb) nanocrystals were firstly synthesized via one-step hydrothermal
route without employing any surfactants. The shape and size of Sr
2
ScF nanocrystals could be readily tuned from nanorods
7
3
+
with 120 nm in length and 50 nm in width to nanopaticles with a uniform diameter of 15 nm by doping 30% Ln with
-
larger ionic radius. Furthermore, the influence of pH values, F sources and different surfactants on the sizes and
morphologies (including nanorods, quadrangular microplates, cube and polyhedron) of the as-prepared products was
systematically investigated and the possible formation mechanism for the products has been proposed. The XRD, SEM,
3
+
EDS, PL analysis and decays lifetimes were used to characterize the products. For DC photoluminescence, the Sr
2
7
ScF :Ln
3
+
3+
3+
3+
nanocrystals show the characteristic f−f transiꢀons with emission colors of bluish violet (Ce , Tm ), green (Tb , Er ,
3
+
3+
3+
3+
Ho ), blue (Dy ) and orange (Eu , Sm ) respectively. Under single wavelength 980 nm excitation, the blue UC emissions
3
+
3+
1
3
3+
of Sr
2
ScF
7
:Yb , Tm nanocrystals at 474 nm due to the
G
4
→ H
6
transition of Tm , the green UC emissions of
3
+
2
4
4
4
Sr
2
2
ScF
ScF
7
:Er nanocrystals at 522/544 nm assigned to the H11/2→ I15/2 / S3/2→ I15/2 transitions and the red UC emissions of
3
+
3+
4
4
3+
Sr
7
:Yb , Er at 660 nm from F9/2→ I15/2 transition of Er were observed respectively. Based on the generation of red,
3
+
3+
3+
green, and blue emissions, the Sr
2 7
ScF :Yb , Er , Tm nanocrystals could produce multicolor, particularly in the white
3
+
3+
3+
3+
region (0.320, 0.330) by controlling the doping concentration of Tm in the Sr
2
ScF
7
:Yb , Er , Tm nanocrystals. It is an
3
+
effective way to modulate the luminescence properties of Sr ScF :Ln by controlling its size and morphology. The as-
2 7
synthesized phosphors might be potentially applied in the fields of color displays, light, photonics and biological imaging.
Introduction
beginning of the transition-metal series. In comparison with
3
+
3+
3+
the optical properties of Y /Ln -based fluorides, Sc -based
On account of the wide range of applications in fluorescent fluorides is particular due to its distinct atomic electron
1
probes, white light emitting diodes (WLEDs), solid state lasers, configuration and much smaller ion radius. As we all know,
7
1
solar cells and many other areas, the inorganic materials the UC emission characteristic is mainly dependent on the
-4
3
+
3+
based on rare earth (RE) ions have attracted a lot of attentions crystal field and the distance of RE -RE in the host lattices.
5
-8
3+
Sc -based fluorides have more excellent UC luminescence
including oxides, fluorides, molybdates and vanadates.
3
Among these inorganic materials, RE-based fluorides represent properties than Y /Ln - based fluorides due to much shorter
+
3+
3
+
3+
3+
a promising fluorescent host matrix because of the merits of distance of Sc -Sc in Sc -based fluorides compared to that
3
the relatively low lattice phonon energy, high chemical in Y /Ln -based fluorides. So, Sc -based fluorides produce a
+
3+
3+
6
,9-12
3+
3+
stability and long-lived luminescence.
effort has recently been put into the synthesis of both Y - and transfer from Yb
Therefore, much closer Er -Yb cation pairs, which is more effective for energy
3
+
3+
3+
to Er
and advantageous for the
3
+
3+
3+
3+
3+
3+
3+
3+
3+
3+
3+
3+
3+
17, 28
Ln (La , Ce , Pr , Nd , Sm , Eu , Gd , Tb , Dy ,Ho , Er , upconversion red emission of Er ions.
Recently, Yu’ group
to improve UC
However, Sc -based fluorides as luminescence intensity and Huang’s group demonstrated
3
+
3+
3+
3+
Tm , Yb , and Lu )-based fluorides with controlled crystalline reported that Sc is doped in NaYF
4
1
2-16
3+
28
phases, shapes and sizes.
the phosphor matrix have largely been neglected.
Scandium, as a rare-earth element, which is found at the very to green ratio when codoped with Yb /Er. In the family of
1
7-27
3+
that Sc -based fluorides give strong emission with a large red
3
+
17
3
+
top of group IIIB in the periodic table and sits at the very Sc -based fluorides, except for the report of Na
NaScF (M = K, Rb, Cs), NaScF , Na ScF , KSc
studies of the synthesis and up/down-conversion
UC/DC) luminescence properties (especially UC white light) of
Sr ScF have not been reported to date.
Up to now, RE-based fluorides with controlled phase,
morphology and chemical composition have been prepared
x
ScF3+x,
M
2
6
1
4
3
6
2 7
F and
7-27
2 6
K NaScF ,
(
2
7
2
9-32
through several approaches.
Among these methods,
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DOI: 10.1039/C6TC05477C
ARTICLE
Journal Name
thermal decomposition, high temperature coprecipitation and displays, backlights and alternatives to general lighting
hydro(solvo)-thermal synthesis are nowadays the three most because it is compact, power-rich, inexpensive and can also be
1
2
3+
3+
3+
common routes. The LaF
BaYF and Na ScF3+x have been fabricated by thermal Yb ions into host materials, a combination of RGB emissions
decomposition.
fluorides can be realized in the method, it requires very toxic the most effective methods for achieving UC white light.
3
LiYF
4
, NaYF
4
, NaGdF
4
, NaLuF
4
,
obtained easily in commerce. By doping Er , Tm , Ho and
3
+
5
x
1
7, 33-38
Although high-quality of RE-based can be obtained in a single inorganic phosphor, which is one of
5
9-62
3
+
fluorinated and oxy-fluorinated carbon species, which always However, there are no reports on white UC light in Ln -doped
1
2, 17, 18
raises some safety concerns.
decomposition method, high-temperature coprecipitation is
favorable for synthesis of fluorides such as LiYF , NaYF
But, it has without any surfactants. Meantime, the morphologies
some drawback including complicated experimental (nanorods, quadrangular microplates, cube and polygons) and
conditions, tedious procedures and high reaction sizes of the Sr ScF nano/microcrystals could be easily adjusted
Compared to thermal Sr
2
7
ScF nanocrystals to date.
Herein, we first report the controlled synthesis of Sr ScF
nanocrystals by a novel Ln -doping hydrothermal method
2
7
3
+
4
4
,
3
9-42
4 4 4 4 4
NaGdF , NaTbF , NaLuF , KGdF and NaScF .
2
7
1
2
−
temperatures. As a result, hydro(solvo)-thermal synthesis is by changing the F sources and pH values. Meanwhile,
more suitable for preparation of highly crystalline fluorides additional surfactant also has a significant impact on the
1
2,22
nanomaterials under relatively mild conditions.
know, organic additives/surfactants play a critical role in a for the formation of Sr
typical hydro(solvo)-thermal synthesis procedure to modify The results indicate that Ln -doped Sr
the crystallographic phase, size and morphology of the exhibit multicolor and controllable DC/UC emissions.
For all we morphology and size of the products. A possible mechanism
2
ScF nano/microcrystals was proposed.
7
3
+
2
7
ScF nanocrystals can
4
3-46
nanomaterials.
However, the complete removal of residual Moreover, under 980 nm excitation, the bright UC white light
ScF nanocrystals by adjusting the tri-
organic additives/surfactants was very difficult by rinsing or is obtained first in Sr
2
7
3
+
3+
3+
post-calcination. For phosphors, they would further act as doped concentration of Yb /Er /Tm . Furthermore, we study
luminescence quenching centers and thus reduce the the effect of size/morphology on the luminescent properties.
7
phosphors' luminescence properties. For nanomaterials,
4
their low solubility in aqueous lead to a poor applications in Experimental section
4
7, 48
biological field. Moreover, some are even toxic.
knowledge, the simplified method is important for RE
luminescent materials, such as lanthanide luminescent CeO
To our Materials
(RE = Sc, Yb, Er, Tm, Ho, Eu, Sm La, Lu and Dy) (99.99 %),
(99.99%) and Tb (99.99%) were acquired from Goring
and films. Thus, it is significant importance High-tech Material Corporation Limited. Strontium chloride
to find a new way to simplify synthetic process of RE-based (SrCl •6H O), ammonium fluoride (NH F), potassium
fluorides. In comparison with previous reports on RE-based fluoride(KF), sodium fluoride (NaF), sodium tetrafluoroborate
2
O
3
2
4 7
O
2
9, 32
49
nanoparticles
2
2
4
3
+
fluorides, we develop a novel one-step route without any (NaBF
surfactant for the preparation of Sr ScF with diverse tunable ammonium Bromide (CTAB), sodiumdodecyl benzenesulfonate
shapes, simultaneously, this method have some advantages of (SDBS), ammonium hydroxide (NH •H O), and hydrochloric
low cost, environmental friendliness, safety and potential for acid (HCl) were obtained from Aladdin Industrial Corporation
large-scale production. (China) and used without further purification. RE Cl (RE = Sc,
4
), trisodium citrate dehydrate (Ci ), hexadecyl trimethyl
2
7
3
2
2
3
3
+
At present, Ln -doping is one of the most effective Yb, Er, Tm, Ho, Ce, Eu, Tb, Sm La, Lu and Dy) were prepared by
approaches to alter the crystallographic phase, size, dissolving corresponding rare earth oxides in dilute HCl and
morphology and electronic configuration of the nanomaterials. then evaporating the excess HCl.
2
3, 50-53
Liu and co-workers reported the conversion of NaYF
4
Synthesis
nanomaterials by a novel Gd -doping approach. Zhu and co- In a typical synthesis process for the Sr
workers reported a novel route by doping rare-earth ions nanocrystals: 2 mmol SrCl , 1mmol ScCl
were dissolved in 30 ml deionized water to
form a transparent solution under strong magnetic stirring at
4
Furthermore, Ln -doped fluoride room temperature for 15 minutes. Subsequently, 8 mmol NH F
3
+
53
3+
3+
2
ScF
7
:10%Yb , 1%Er
2
3
, a certain amount of
3
+
3+
3+
3+
3+
3+
3 3
(RE ) with large ionic radii (such as La , Ce , Sm , Eu , Tb , YbCl and ErCl
3
+
3+
3+
2 7
Dy , Yb and Lu ) for aspect ratio modification of KSc F
2
3
3+
nanocrystals (NCs).
nanocrystals have aroused fast growing interest on the basis of was dropwise into the above solution under vigorous stirring,
their superior physicochemical features such as low toxicity, and a white colloidal solution was formed. Then, the pH value
3 2
large antenna-generated Stokes and/or anti-Stokes shifts, high of the mixture was adjusted to 7 by adding NH •H O solution
resistance to photobleaching and narrow emission bands as drop by drop. After additional agitation for 30 min, the
compared to conventional molecular probes like organic obtained white colloidal solution was transferred into a 50 ml
1
2-17
dyes.
biological assays and medical imaging.
much larger NIR (980 nm) absorption cross-section which are After cooling down to room temperature, the final samples
So, these materials can be applied for diagnostics polytetrafluoroethylene autoclave (filled up to 80% of its total
5
4-58
3+
Yb ions have a volume) which was sealed and maintained at 220 °C for 24 h.
3
+
often co-doped as excellent sensitizers along with Er and were collected by centrifugation, washed several times with
3
Ho to yield strong red and green UC emissions, or together deionized water and absolute ethanol, and dried in air at 60 °C.
+
3
+
with Tm for blue UC emissions. On the other hand, it is well- Meantime, the synthesis of the other Sr
known that UC white light has a wide range of applications in nano/microcrystals was similar to the above procedure.
2 7
ScF
2
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ARTICLE
Characterization
The crystal structures and phase purities were analyzed by
powder X-ray diffraction (XRD) performed on a Purkinje
General Instrument MSALXD3using Cu Kα radiation (λ =
-
1
0
.15406 nm) at a scanning rate of 10° min in the 2θ range
from 23° to 60°, 20 mA, 36kV. The morphology and energy
dispersive spectrometry (EDS) spectrum of samples were
investigated by a field emission scanning electron microscope
(FE-SEM, XL30, Philips) operated at an accelerating voltage of
1
0kV. The DC fluorescent spectra were recorded a Hitachi F-
000 spectrophotometer carried with a 150W xenon lamp as
7
the excitation source. The UC fluorescent spectra were
obtained using a 980nm laser from MDL-N-980-8W as the
excitation source and detected by a LS 55 (PerkinElmer) from
400 to 750nm. The decay lifetimes were measured by FLS980
(Edinburgh Instrument). All the measurements were
performed at room temperature.
Results and discussion
Structure and phase
The Sr ScF has been found to be the pure monoclinic phase
2
7
with the space group P21/c (#14) (a = 5.450 Å, b = 12.190 Å, c
8.236 Å and Z = 4). The detailed crystallographic data and
structural parameters for Sr ScF crystal are listed in table S1.
=
2
7
2
+
The structure of the Sr ScF crystal and the sites of Sr and
2
7
3
Sc polyhedrons are presented in Fig. 1A. The cation Sr
+
2+
occupies a 9-coordination environment, and nine coordinated
fluorine atom around to form single cap-square antiprism.
3
Each cation Sc is coordinated by its nearest seven fluorine
+
3
+
atoms to form an irregular enneahedron in which the Sc
crystallographic sites can serve as symcenter for dopant ions
3
Ln ). The 7-fold Sc and 9-fold Sr join by sharing edges and
+
3+
2+
(
3
vertices, respectively. The Sc were commonly considered to
+
3
be replaced by Ln based on their similar valence and ionic
+
3
+
3+
radii (Sc : CN = 7, r = 0.87 Å); Ln , (Ln =Lu, Yb, Tm, Dy, Tb, Eu,
Sm, La; CN = 7, r = 0.92-1.1 Å). The EDS in Fig. 1B suggests that
the Sr ScF nanocrystals synthesized by hydrothermal method
2
7
without any surfactant only consists of Sr, Sc and F elements
with the corresponding ratio of 2.1 : 1 : 6.9, which is very close
to the stoichiometric value.
Fig. 1C shows the XRD patterns of pure Sr
2
ScF
Sr ScF :30%Ln . All the diffraction peaks can be assigned to a
7
and
3
+
2
7
2 7
pure monoclinic Sr ScF phase, which coincides well with the
Standards Card (JCPDS no. 28-1251). No extra diffraction peaks
are observed, indicating that the high purity and crystallinity of
3
+
the products are obtained and Ln (Ln = Lu, Yb, Tm, Dy, Tb, Eu,
Sm, La) are completely dissolved in the Sr ScF nanocrystals.
The XRD peaks obviously shift toward low 2θ direction with a Fig. 1 (A) The structure of the Sr
2
7
2
crystal and the sites of Sr and Sc
+
3+
2
ScF
7
3
+
larger ionic radius of the doping Ln (r = 0.92-1.1 Å) compared polyhedrons; (B) EDS spectrum of pure Sr
3
ScF crystal; (C) XRD patterns of
2 7
3
to that of Sc (r = 0.87 Å) owing to lattice expansion.
+
22, 63
+
It is pure Sr ScF (a) and Sr ScF :30%Ln (b-i).
2 7 2 7
3
worth noting that the addition of Ln into Sr
+
2
ScF
differences in diffraction peaks of (121), (130), (240) and (162)
7
cause some
the diffraction peaks of (240) and (162) tend to be broadened
3+
with increasing the radius of Ln , suggesting that the larger-
12
sized dopants are preferred to form smaller nanocrystals.
3
because of the doping of Ln with a larger ionic radius. With
+
3
+
increasing of the Ln radius from 0.92 Å to 1.1 Å, the peak
intensity of (130) become stronger than that of (121), which
suggests the preferential orientation growth along the (130)
direction to some degree. Interestingly, it is also observed that
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Morphology
Fig. 3 SEM images of Sr
2
ScF
7
crystals prepared at different pH values and
3
+
-
nanocrystals, (B) 30% Lu , (C) 30% using different F source, respectively. The pH and F source are indicated in
-
Fig. 2 SEM images of (A) pure Sr
2
ScF
7
3
+
3+
3+
3+
3+
Yb , (D) 30% Tm , (E) 30% Dy , (F) 30% Tb , (G) 30% Eu , (H) 30% Sm
3+
each picture.
3
+
2 7
and (I) 30% La doped Sr ScF nanocrystals, respectively.
-
It was found that the pH values and F sources of the initial
More important, Ln doping with larger radius not only affects reaction solutions have a large impact on the morphologies
the diffraction peaks of Sr ScF nanocrystals, but also plays an and sizes of the Sr ScF crystals. The SEM images of the Sr ScF
important role on their morphology. The SEM images of the crystals (S -S ) prepared at different pH with NH F as the F
undoped and doped with 30% Ln (Ln = Lu, Yb, Tm, Dy, Tb, Eu, source are shown in Fig. 3A-C. It is obvious that the nanorods
Sm and La) Sr ScF nanocrystals are shown in Fig. 2. Based on obtained at pH = 2 with average size of 90 nm in length are
the SEM results, table S2 shows the effect of the doping Ln
on the length and width of the Sr ScF nanocrystals. Without further increasing the pH to 10 (S
deliberately added Ln , the SEM image (Fig. 2A) of the Sr ScF of the products varies greatly as shown in Fig. 3C. The product
is relatively uniform and monodisperse nanorods with 120 nm is composed of irregular polyhedron with a diameter of 18 µm
in length and 50 nm in width. However, in the presence of 30% and some nanorods are covered on its surface. If NH F was
nanocrystals replaced by NaF as F source, the SEM images of as-prepared
3
+
2
7
2
7
2
7
-
1
3
4
3
+
2
7
3
+
smaller than that obtained at pH = 7 (110 nm in length). With
), the morphology and size
2
7
3
3
+
2
7
4
3
+
-
Ln dopant ions, the size and shape of the Sr
are remarkably modified. As shown in Fig. 2B, the Lu -doped products (S
Sr ScF product is still composed of monodisperse nanorods Fig. 3D-F. As can be seen, all the products consist of a large
but the decrease in size (80 nm in length and 40 nm in width). amount of nanorods whereas the length of the products
2 7
ScF
3
+
4
6
-S ) at different pH values (2, 7, 10) are shown in
2
7
3+
3+
When lanthanide dopants from Lu to La with the radius increases remarkably from 120 nm to 1.5 µm and the width
from 0.92 Å to 1.1 Å were introduced into the crystal lattice of increases from 40 nm to 80 nm. The Fig. 3G-I illustrate the SEM
the Sr
obviously changed and composed of spherically shaped as F source. When the starting pH = 2 (S
nanopaticles with a uniform diameter (from 50 nm to 15 nm). homogeneous and well-shaped cube with sizes of about 1 μm
As a result, the size of the Sr ScF nanocrystals decreases were formed, as displayed in Fig. 3G. It is notely that there is a
monotonously with increasing of Ln ionic radius, which is also hole in the center of cube. As the pH value increased to 7 (S
in agreement with the results from the XRD analysis in Fig. 1C. not only cubes but also a plenty of quadrangular microplates
The size evolution of Sr ScF nanocrystals can be partly (5 μm in size) were obtained in the Fig. 3H. Upon further
attributed to that the dopants with a larger ionic radius could increasing the pH value to 10 (S ), the obtained products were
decelerate the anisotropic crystalline growth. In the case of mainly composed of anomalous polyhedron and a small
2
ScF
7
crystals, the morphology of the product is images of Sr
2
ScF
7
crystals obtained at different pH with NaBF
4
-
7
), uniform,
2
7
+
3
8
),
2
7
9
3
+
3+
substitution of Sc by Ln with larger radius, the electron quantity of cubes (Fig. 3I). The main reasons for the
charge density on the surface of the Sr ScF nanocrystals phenomena is that: Firstly, the equilibrium between the
increases. The change of electron charge density on the chemical potential and the rate of ionic migration could be
2
7
6
6
surface of nanocrystals can substantially slow the diffusion of affected by the pH value in the initial solution, then the
-
negatively charged F ions to the surface because of an nucleation rate could be changed, usually, as the pH increases,
increase in charge repulsion, which results in a tunable the slower nucleation rate will result in a crystal with a large
1
2, 13, 63-65
28
size. In the case of Sr
reduction of the Sr
2
ScF
7
nanocrystals.
2 7
ScF , the nucleation rate is strongly
-
dependent on the competition of OH and F . With the increase
-
-
-
3+
2+
of OH , the chelation between OH and Sc (Sr ) take place,
-
which will inhibit the precipitation of F and Sc (Sr ) to some
3+
2+
4
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-
extent, thus decreasing nucleation rate and resulting in larger Scheme 1. Schematic illustration for the effects of F source, pH value and
-
2 7
2 7
crystals. Secondly, the F source in the Sr ScF system (other surfactants on the Sr ScF crystals, respectively.
reaction parameters remaining constant) has a great influence
on formation of different crystal structures and morphologies.
-
is used as F source, the BF
-
In particular, When NaBF
4
4
is
3
-
-
and F ions, which will affect
slowly hydrolyzed to release BO
3
6
7
the rate of crystal nucleation and crystal growth. In addition,
at the early stage of the reactions, owing to the strong
+
+
−
interactions of the cations (NH
4
and Na ) and the anions (OH ,
, and F ), these cations can be selectively adsorbed on
different surfaces of the initial crystal nucleus, and then
3
-
-
BO
3
6
8
influence the corresponding surface energy. Finally, various
morphologies and sizes of Sr ScF crystals can be obtained. The
2
7
formation and morphology evolution of the S ScF crystals are
r2
7
-
controlled by varying the pH values and F sources as
illustrated in Scheme 1. In conclude, the mass production of
size- and morphology-controlled Sr ScF nano-/microcrystals
2
7
can be effectively synthesized by simple surfactant-free
hydrothermal method.
To obtain well-defined crystals with uniform morphology
for UC/DC luminescence, a series of experiments with different
surfactants in Sr ScF system under the same conditions were
2
7
carried out. The typical XRD patterns and SEM images of
Sr ScF crystals are given in Fig. 4. As displayed in Fig. 4A, all
2
7
the peaks can be ascribed to the pure monoclinic Sr ScF phase the uniformly distributed Sr ScF nanorods (S ) with diameter
2
7
2
7
10
(
JCPDS no. 28-1251) and no diffraction peaks of any other of about 30 nm and length of 110 nm were obtained in the
3
+
phases are detected. It is clear that the diffraction peaks of the presence of Ci . Irregular polyhedrons (S ) with sizes in the
1
1
3
Sr ScF crystals prepared with different surfactants from Ci to range of 3–8 μm can be observed in the Fig. 4C when CTAB
+
2
7
SDBS become narrower and sharper, indicating the increase of was used as surfactant. Whereas, the Sr ScF crystals (S ) are
2
7
12
the products’ size. Notely, the relative peak intensity of the composed of numerous prismatic structures (7 μm in width, 15
022) for the products with SDBS is visibly enhanced, implying μm in length) when SDBS assisted hydrothermal process was
that the prismatic structures of Sr ScF7 crystals grow carried out. It can be found that the size of Sr ScF crystals
(
2
2
7
3
+
preferentially along the (022) direction. As displayed in Fig. 4B, become larger along with the change of surfactants from Ci
to SDBS , which is consistent with the XRD results (Fig. 4A). The
3
+
reasons for this phenomenon are as follows: on one hand, Ci ,
CTAB and SDBS are regarded as excellent chelating agents that
slow down the nucleation and subsequent further aggregation
7
9,70
of the nanoparticles,
therefore, the Sr ScF crystals
2 7
produced with surfactants are larger than that without
surfactants (Fig. 1A); on the other hand, various surfactants
selectively adsorb on the specific crystal facets of Sr ScF7
2
owing to their different coordination modes and specific
molecular complementarity, which directly affects the
anisotropic growth of the crystals, resulting in the different
7
1
morphologies and sizes of nano/microcrystals.
corresponding growth process can be explained as in Scheme
The
1.
Photoluminescence properties
Our experimental results and previous investigations both
2 7
indicate that Sr ScF is an excellent host for the luminescence
of various optically active lanthanide ions just like the same
6
type of Sr YF . Therefore, we mainly focus on the DC/UC
Fig. 4 XRD patterns of Sr
crystals with different surfactants (B: Ci ; C: CTAB; D: SDBS).
2
ScF
7
(A) and SEM images of the obtained Sr ScF
2
7
2
7
3
+
luminescence properties of Ce, Tb, Eu, Sm, Dy, Er, Ho, Tm
single-doped, Yb/Er, Yb/Tm co-doped and Yb/Er/Tm tri-doped
2 7 2
Sr ScF nanocrystals (S ).
DC photoluminescence
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Journal Name
6
respectively. On excitation into the 4f –4f 5d transition at
7
8
7
1
2
4
22 nm, the emission spectrum exhibits four lines centered at
89, 546, 586 and 624 nm, originating from transitions from
5
7
3+
the D
4
excited state to the FJ (J = 6, 5, 4, 3) ground states of Tb .
The most prominent emission peak which is attributed to the
5
7
→ F
3+
5
transition of Tb is seated at 546 nm. Fig. 5C shows
D
4
3
+
the PL excitation and emission spectra of the Sr
2
7
ScF :9%Eu
phosphors. With monitoring of the wavelength at 594 nm, the
excitation spectrum is composed of many sharp peaks with a
band maximum at 394 nm, which are ascribed to the typical
3
+
intraconfigurational f–f transitions of the Eu ions. They are
7
due to 328 nm ( F
5
→ H
7
), 362 nm ( F
5
→ D
0
6
0
4
), 381 nm
7
5
7
5
7
F → G ), 394 nm ( F → L ) and 465 nm ( F → D ),
5
(
0
2
0
6
0
2
3
+
respectively. Under 394 nm excitation, the emissions of Eu
5
7
5
7
are located at 565 nm ( D → F ), 594 nm ( D → F ), 619 nm
0
0
0
1
5
7
5
7
5
7
(
D → F ), 650 nm ( D → F ) and 698 nm ( D → F ),
0 2 0 3 0 4
respectively. The strongest emission centered at 594 nm
5
7
belongs to the D → F magnetic dipole transition, suggesting
0
1
3
+
that the Eu
ions are embedded in the symmetric
7
environment according to the Judd–Ofelt theory. It is
3
noteworthy that Sr ScF :1%Dy phosphors shows a blue
+
2
7
luminescence (Fig. 5E). In the emission spectrum, two main
4
6
peaks at 482 nm ( F → H15/2, magnetic dipole) in the blue
9
/2
4
region and 577 nm ( F → H , electric dipole) in the yellow
6
9
/2
13/2
4
6
region are observed. Among them, the F → H transition
15/2
9
/2
3
+
is dominant because the Dy is located at a symmetry local
3
site in the Sr ScF host lattices, just like the Eu D → F in
+
5
7
2
7
0
1
Sr ScF host (Fig. 5C). Detailed assignment for luminescent
2
7
properties is listed in table S3. All the doped lanthanide ions
3
+
n
Ln ) show their characteristic transitions within 4f electron
(
configuration in Sr ScF host lattice with emission colors of
2
7
3+
3
+
3+
3+
3+
3+
3+
Fig. 5 DC photoluminescence excitation and emission spectra of Sr
2
ScF
7
:Ln
.
bluish violet (Ce , Tm ), green (Tb , Er , Ho ), blue (Dy )
3
+
3+
and orange (Eu ,Sm ), respectively. The corresponding CIE
The performance of phosphors is easily influenced by the chromaticity diagram is presented in Fig. S2.
7
2
doping concentration of the luminescent center. With UC photoluminescence
3
+
increasing concentration of doped Ln , the distance of the Fig. 6A displays the UC photoluminescence emission spectra of
3
+
3+
3+
luminescent center becomes short enough to bring about Sr ScF :x%Yb ,1%Er
nanocrystals with variable Yb
2
7
3
+
concentration quenching of Ln . So, it is very important to find concentrations from 0 mol% to 10 mol%. It is found that the
the optimum doping concentration. The results have been intensity of green emission (I ) decreased while the intensity
G
discussed in Fig. S1.
The photoluminescence (PL) excitation and emission concentration of Yb . Fig. 6B gives the intensity ratios of I
of red emission (I ) enhanced with increase of the doping
R
3
+
G
3
+
spectra Sr
2
ScF
7
:6%Ce phosphors are shown in Fig. 5A. By and I to the total integrated intensity I
in the range of
(G+R)
R
means of monitoring at 351 nm, the excitation spectrum 400–750 nm, respectively, which intuitively reflect the change
3
+
consists of a broad and strong band with a maximum at 294 of I and I with the varied concentration of Yb ions. Fig. 6C
G
R
nm and a weaker band at 259 nm, which attribute to the shows
the
3+
CIE
3+
chromaticity
nanocrystals.
coordinates
of
3+
2
3+
transitions from the F5/2 ground state of Ce to the excited Sr ScF :x%Yb ,1%Er
When the Yb
2
7
3
+
Ce 5d states split. Upon excitation at 294 nm, the emission concentration changes from 0% to 10%, the corresponding
spectrum of Sr ScF :6%Ce phosphors displays a palpable chromaticity coordinates (x, y) systematically alter from (0.290,
2 7
3
+
peak centered at 351 nm, which corresponds to the transitions 0.670) to (0.398, 0.377) and the corresponding color points
from the lowest excited 5d state to the 4f ground state. The gradually alter from green to red. A similar result is also
3
+
3+
3+
excitation and emission spectra of Sr
2
ScF
7
:12%Tb phosphors observed from other Yb
and Er
codoped fluoride
6
,9,73
are presented in Fig. 5B. The excitation spectrum of nanocrystals.
Sr ScF :12%Tb monitored with 546 nm emission (Tb : Er keeping in the green-emitting levels of H / S and
This phenomenon is due to relatively fewer
2
3
+
3+
3+
4
11/2 3/2
2 7
7
→ F
5
3+
D
4
5
) consists of a strong band from 200 to 400 nm with a more Er ions remaining in the red-emitting
maximum at 222 nm and a weak band at 265 nm, which
7
correspond to the spin-allowed ( F
7
→ D
6
J
) transition and the
7
spin-forbidden ( F → D ) transition of the 4f –4f 5d transition,
9
8
7
1
6 J
6
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ARTICLE
4
level of F9/2 (Fig. 9). On one hand, the interatomic distance of
3
+
Yb -Er in the Sr
3+
2 7
ScF host lattice would decrease with
3
increase of the concentration of Yb ions, which will produce
3
two energy-back-transfer processes from Er to Yb . The
+
+
3+
4
3+
2
3+
4
energy back-transfer (BET1) of S3/2 (Er ) + F7/2 (Yb ) → I13/2
3
Er ) + F5/2 (Yb ) should subsequently reduce the population
+
2
3+
(
4
2
in excited levels of S3/2 ( H11/2), resulting in the decrease of
2
4
4
green emission ( H11/2/ S3/2→ I15/2). At the same time, the
4
energy transfer leads to the saturation of the I13/2 (Er ) state,
3+
3
and then the excited Yb ions transfer energy to Er ions
+
3+
2
3+
4
3+
through the energy transfer process F5/2 (Yb ) + I13/2 (Er ) →
2
3+
4
3+
9/2 (Er ), which can directly increase the
F
7/2 (Yb ) +
F
4
number of electrons in the F9/2 level, resulting in the
4
enhancement of red emission ( F → I ). Furthermore, the
4
73
9
/2
15/2
+ 4
photoluminescence decay curves of Er S3/2 → I
3
4
emission
15/2
level (λex = 980 nm, λem = 544 nm) were also measured to
confirm the existence of BET1. Fig. 10A presents the
3
representative decay curves of Er which are all well fitted
+
into a single exponential function as I(t) = I exp(−t/τ) (τ is the
0
3
+
corresponding lifetime). Clearly, when 10% Yb
was
3
+
introduced, the lifetimes of Er (544 nm) decrease from 85.7
3
+
μs to 67.9 μs, which is a strong evidence for the BET1 from Er
3
to Yb in Sr ScF host. In addition, The energy back-transfer
+
2
7
4
3+
2
3+
4
process (BET2) of F (Er ) + F (Yb ) → I
3+
2
(Er ) + F
5/2
7
/2
7/2
11/2
3
Yb ) should suppress the number of electrons in the excited
+
(
4
3+
F7/2 (Er ) level at higher concentrations of Yb . This leads to a
3+
2
smaller population of the H
4
and S green-emitting levels
3/2
1
1/2
7
4
and the decrease of the green emission intensity. On the
4
other hand, the number of electrons in F red-emitting level
9
/2
2
increase directly while the number of electrons in H
and
1/2
1
4
S3/2 green-emitting levels reduce indirectly by the cross
4
4
relaxation ( F
4
→ F9/2 + F9/2) in Er . A detailed
4
3+ 4
+
I11/2
7
/2
explanation is shown in Fig. 9.
3
+
3+
2 7
Fig. 6 (A) UC photoluminescence emission spectra of Sr ScF :x%Yb ,1%Er
Fig.7 UC photoluminescence emission spectra and the corresponding
3
nanocrystals under 980 nm excitation; (B) The ratios of green emission
intensity I and red emission intensity I to the total integrated intensity
(G+R) in the range of 400–750 nm, respectively; (C) The CIE chromaticity
+
2 7
luminescent photographs of the Sr ScF :Ln nanocrystals under 980 nm
G
R
3
:10%Yb ,2%Tm
+
3+
3+
,
excitation: (a) Sr ScF
3+
2
7
,
(b) Sr
2
ScF
7
:1%Er
(c)
I
3+
2 7
Sr ScF :10%Yb ,1%Er .
3+
3+
coordinates of Sr
2 7
ScF :x%Yb ,1%Er nanocrystals (a: x = 0; b: x = 2.5; c: x =
5
; d: x = 7.5; e: x = 10).
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3
+
3+
3+
2 7
Fig. 7 displays the UC photoluminescence emission spectra Sr ScF :10%Yb ,1%Er ,y%Tm nanocrystals vary from yellow
3
+
(
400–750nm) of Sr
2 7
ScF :Ln nanocrystals under 980 nm region (0.365, 0.415)
excitation. The UC photoluminescence emission spectra of
3
+
3+
Sr
2 7
ScF :10%Yb ,2%Tm (Fig. 7a) shows blue emission mainly
1
3
→ H
located at 474 nm which is attributed to the
3
transitions of Tm ions. Although a red UC photoluminescence
G
4
6
+
1
3
3+
due to the
4 4
G → F transition of Tm appears in the
3
+
3+
Sr
2 7
ScF :10%Yb , 2%Tm nanocrystals, it is too weak to be
3
considered in this work. Yb plays important role in the blue
+
3
+
3+
emission spectra of Sr
2 7
ScF :10%Yb , 2%Tm nanocrystals,
because we cannot detect pronounced UC blue emission in
3
+
Tm
single doped Sr
2
ScF
7
nanocrystals. The UC
3
photoluminescence emission spectra of Sr ScF :1%Er (Fig. 7b)
+
2
7
shows strong green emission at 522 nm and 544 nm which are
3+
2
4
ascribed to the H1 → I
4
4
and S → I
transitions of Er
1/2
15/2
3/2
15/2
respectively, and a quite weak band at 660 nm which is
3+
transition of Er . However, it can
4
assigned to the F9 → I
4
/2
15/2
be observed that the UC emission color changes markedly
3
from green to red when Yb ions were codoped with Er into
+
3+
the Sr ScF7 host lattice. Compared to the UC
2
3
+
photoluminescence emission spectra of Sr ScF :1%Er
2
7
nanocrystals, the UC photoluminescence emission spectra of
3
+
3+
Sr ScF :10%Yb ,1%Er (Fig. 7c) gives strong red emission at
2
7
4
60 nm which is attributed to the F → I
4
6
transition of
3+
9
/2
15/2
3
Er . The chromaticity coordinates of the Sr ScF :10%Yb ,
+
2
7
3
%Tm ,
+
3+
3+
3+
2
Sr ScF :1%Er
2
and
Sr ScF :10%Yb ,1%Er
2 7
7
nanocrystals are (0.13, 0.13), (0.29, 0.67) and (0.40, 0.38)
respectively (Fig. S3), which can be confirmed by the
corresponding luminescent photographs under 980 nm
excitation (insets in Fig. 7).
Based on the above analysis, we speculate that it is
possible to produce the white UC photoluminescence by
3
+
3+
3+
adding an appropriate ratio of Yb /Er /Tm into Sr ScF
2
7
nanocrystals. To prove our conjecture,
a
series of
3
Sr ScF :10%Yb , 1%Er , y%Tm nanocrystals doped with
+
3+
3+
2
7
3
+
different Tm
concentrations (y = 0.1-2) have been
synthesized. The UC photoluminescence emission spectra of
these samples are presented in Fig. 8A. It can be found that
the
UC
photoluminescence
emission
spectra
of
Fig.
Sr ScF
The
Sr ScF
8
(A) UC photoluminescence emission spectra of the
3
+
3+
Sr ScF :10%Yb ,1%Er ,y%Tm nanocrystals are composed of
3+
3+
3+
3+
2
7
2
7
:10%Yb ,1%Er ,y%Tm nanocrystals under 980 nm excitation; (B)
corresponding CIE chromaticity coordinates of the
:10%Yb ,1%Er ,y%Tm nanocrystals (a: y = 0.1; b: y = 0.5; c: y =1;
1
blue emission at 474 nm due to G → H transitions of Tm ,
3
3+
4
6
3+
3+
3+
green emission at 522 nm and 544 nm arising from the
2
2
7
4
4
4
3+
transitions of Er and red
H1 → I
and S3/2→ I
1/2
15/2
15/2
d: y = 2).
3+
to white region (0.316, 0.322) by altering Tm concentration.
4
emission at 660 nm originating in the F → I
4
transition of
9
/2
15/2
3
+
Er . It is noteworthy that the shape of UC band at 650 nm Furthermore, when
y
=
1, the ideal white UC
3+
1
from the transition G
3
→ H
3+
3+
Sr ScF :10%Yb ,1%Er ,1%Tm
2 7
3+
4
4
of Tm in Fig. 7a is consistent photoluminescence
in
3
+
3+
with that of Er in Fig. 7c. So, the contribution of Tm to the nanocrystals with chromaticity coordinates of (0.320, 0.330) is
red UC photoluminescence emission band in Fig. 8A can be obtained here for the first time and the corresponding
7
4, 75
neglected owing to the following two reasons:
one part is luminescent photograph is also shown in Fig. 8A for direct
that the red emission band intensity in Fig. 7a is much lower comparison.
than that of the blue emission band; another part is that the
shape of the red band in Fig. 8A is exactly the same as that of efficiency of the PL, but also brings out UC photoluminescence
It is well known that codoping not only increases the
7
4
3+
3
+
Er ions in Fig. 7c. It is also clearly observed that the blue between the donor and acceptor ions. The Yb was often
chosen as sensitizer in Yb -Er , Yb -Tm -codoped and Yb -
3
+
3+
3+
3+
3+
emission is relatively enhanced with increasing the
3
+
3+
3
+
Er -Tm tridoped systems due to a much longer excited state
lifetime and a larger absorption cross section around 980 nm.
concentration of Tm from 0.1% to 2%. Additionally, in Fig. 8B,
the corresponding CIE chromaticity coordinates of
8
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The latter leads to energy transfer between the Yb emission
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3
+
2
2
3+
4
4
3+
F
5/2→ F7/2 and the Er absorption I11/2→ I15/2 or the Tm
3
Fig. 9 Energy level diagrams of the Yb , Er and Tm ions as well as the proposed UC emission processes.
+
3+
3+
3
absorption H → H . The energy level diagrams of the Yb , photon process. The reason for this phenomenon is that Tm
3
75
3+
3+
5
3+
6
3
+
Er and Tm ions as well as the proposed UC emission has no ground or excited state absorption (GSA or ESA) that
3
processes of the Er and Tm is illustrated in Fig. 9. The matches the 980 nm photon. First, Under 980 nm excitation,
+
3+
2
previous literatures have reported the mechanism of the UC the photons can be absorbed by F states in Yb , then the
3+
5
/2
3
green emission of the Er .
+ 73-76
3+
3+
The absorption transition nonresonant ET from Yb to Tm takes place to transfer the
4
between the ground state of I
4
3
energy to H5 level in Tm . And lastly, the photons relax
3+
and the excited level I
11/2
1
5/2
3
GSA) of Er match well with the energy from 980 nm rapidly to the F level by nonradiative multiphonon decay. A
+
3
(
4
3
excitation. In the absence of Yb , Sr ScF :1%Er nanocrystals second nonresonant ET from Yb to Tm can populate higher
+
3+
3+
3+
2
7
3
3
F2 and F3 energetic states from F4 of the Tm , and
3
3+
emits green emission and the details are given as below:
3
3+
Firstly, under the excitation of 980 nm, the photons are mostly subsequently relax to H level of Tm by multiphonon decay.
4
3
absorbed by Er from its ground state ( I15/2) to the excited A third ET finally populates the G level, and then the strong
+
4
1
4
4
energy level ( I ), and then, the excited electrons jump from blue emission at 474 nm ( G → H ) and weak red emission at
1
3
1
4
1/2
4
6
4
the I1 to the F level (ESA). Subsequent the energy in F
4
1
3
75,76
650 nm ( G → F ) occur.
4 4
1/2
7/2
7/2
2
level can transfer to H11/2
4
4
S3/2 and F9/2 levels via
73-75, 77
,
According to the previous literature,
some other ET
3+
3
+
nonradiative relaxation. Finally, the energy in these levels processes might occur between the Er and Tm in the
return to the ground state, emitting the most strong green complex tri-doped Sr Sc F system besides the main ET
2
3+
2 7
3
+
2
4
4
3+
3+
emissions at 522 nm and 544 nm of Er ( H / S → I15/2) processes between Yb and Er /Tm . The nearly resonant
1
1/2
4
3/2
4
1
3+
4
as well as very weak red emission at 660 nm ( F → I15/2). For cross relaxation processes of G (Tm ) + I
3+
3
(Er ) → F
4
9
/2
4
15/2
3
+
3+
3+
4
3+
3
red emission of the Sr ScF :10%Yb ,1%Er nanocrystals, the (Tm ) + F (Er ) and H (Tm ) + I (Er ) → H (Tm ) +
3+
4
3+
3
3+
2
7
9/2
4
13/2
6
4
3+
S3/2 (Er ) are illustrated in Fig. 9. This two energy-transfer
mechanism of UC emission mainly comes from two sides: one
3
+
3+
3+
main part is that the two-photon energy transfer (ET) from the behavior in the Yb -Er -Tm tridoped Sr ScF nanocrystals
2
7
3
excited Yb to Er due to a much larger absorption cross can be confirmed by the decay curve behaviors of the G
+
3+
1
4
3
+
3+
3
3
3
section and concentration of Yb than that of Er ; and little → H and H → H transitions of Tm respectively, as shown
3+
6
4
6
3
part is from Er ground/excited state absorption (GSA/ESA). At
+
2
first, the electrons in the ground state ( F ) of Yb are excited
3+
7
/2
2
into its F5/2 level by 980 nm excitation, then the energy
3
+
3+
4
3+
transfers from a excited Yb to Er ( I11/2), and a second Yb
ion transfers its energy again. The two step results in electrons
4
transfer from I11/2 level to high excited F7/2 state of Er . At
4
3+
4
2
4
4
last, electrons at F7/2 state populate its H11/2/ S3/2, and F9/2
states via relaxation and other energy transfer process, then
return to its
60 nm corresponding to
22/544 nm corresponding to H11/2/ S3/2→ I15/2 (weak). The
detailed explanation can be seen in the above paragraph (Fig.
4F9/2 ground state, engendering the emissions at
4
4
6
F9/2→ I15/2 (most strong) and
2
4
4
5
3
+
3+
6
). For blue emission of the Sr
2 7
ScF :10%Yb ,2%Tm
3
nanocrystals, the UC photoluminescence of Tm comes from
3
energy transfer processes from Yb to Tm due to the three-
+
+
3+
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ARTICLE
Journal Name
3
+
4
Fig. 10 (A) The decay curves of the S3/2
4
3+
3+
2 7
Fig. 11 The photoluminescence emission spectra of the Sr ScF :10%Yb ,
3+ 3+
→
I
15/2 of Er in the Sr
2 7
ScF :1%Er
1
2 7
%Er (A) and Sr ScF :5%Eu (B) samples with various morphologies.
3
+
3+
and Sr
of the
:10%Yb ,1%Er ,1%Tm nanocrystals, respectively.
2 7
ScF :10%Yb ,1%Er nanocrystals, respectively; (B) the decay curves
1
G
3
3+
3+
3+
4
→ H
6
of Tm
in the Sr
2
ScF
7
:10%Yb ,1%Tm
and
Under 980 nm laser excitation (Fig. 11A), three UC emission peaks
3+
3+
3+
Sr2ScF
7
2
4
4
4
at 522, 544 and 660 nm are assigned to H11/2→ I15/2, S3/2→ I
15/2
4
4
3+
and F → I of Er , respectively. However, the intensity ratio of
15/2
3
+
9/2
in Fig. 10B and Fig. S4. The luminescence decay curves of Tm
red to green emission (Rr/g) decreases as the morphologies of
samples change from nanorods (Rr/g = 5.14 for S ) to polyhedrons
3
+
3+
in
Sr
the
Sr
2
ScF
7
3+
:10%Yb ,1%Tm
and
:10%Yb ,1%Er ,1%Tm can be well fitted by the single
exp(−t/τ). Obviously, we can
3
+
3+
2
2
ScF
7
(
Rr/g = 0.88 for S11) and further to the prismatic structures (Rr/g =
exponential function I(t) = I
observe that the decay time of Tm
0
0
3
.58 for S12). As the size of the samples increases from S to S (Fig.
2 12
3
+
in the
:10%Yb ,1%Er ,1%Tm nanocrystals is shorter than
B and Fig. 4C-D), the surface-to-volume ratio of the samples
3
+
3+
3+
Sr
that in Sr
evidence for the ET from Tm
2
ScF
7
decreases. Furthermore, surface defects- and ligands-induced
quenching of UC luminescence become more important, which
3
+
3+
2
ScF
7
:10%Yb ,1%Tm nanocrystals, which is a strong
3
+
3+
to Er
in the
modifies the relative population among various excited states
3
+
3+
3+
Sr ScF :10%Yb ,1%Er ,1%Tm nanocrystals. In addition, the
7
77, 78
2
through phonon-assisted nonradiative relaxations.
Upon
3
ET from Tm to Er is an another reason why the contribution
+
3+
3+
excitation of Eu at 394 nm (Fig. 11B), all the emission spectra (594
3
+
of
Tm
ions
3
to
3+
the
red
UC
emission
in
3+
nm and 619 nm) of Sr ScF :5%Eu samples are similar in shape
+
3+
Sr ScF :10%Yb ,1%Er ,1%Tm nanocrystals (Fig. 8A) can be
2
7
2
7
except for the relative intensities. Apparently, the relative emission
neglected.
intensity of S12 is higher than that of others (S and S11) due to the
2
different morphologies/sizes. In general, the defects of crystal
Morphology/size-dependent luminescent properties
surfaces can lead to nonradiative recombination between electrons
To investigate the influence of morphology/size on the luminescent
properties, the photoluminescence emission spectra of the
7, 46, 67
and holes, which will reduce luminescence intensity.
The
surface-to-volume ratio of the samples decreases along with
increase of size, which reduces defects on its crystal surfaces.
Therefore, the sample (S12, Fig. 4D) with the largest size shows high
3
+
3+
3+
Sr ScF :10%Yb , 1%Er (A) and Sr ScF :5%Eu (B) samples with
2
7
2
7
various morphologies are presented in Fig. 11, respectively.
1
0 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6TC05477C
ARTICLE
luminescence intensity. In conclusion, the control of the
size/morphology of crystal is another effective way to modulate the
4
H. Lin, B. Wang, Q. M. Huang, F. Huang, J. Xu, H. Chen, Z. B.
Lin, J. M. Wang, T. Hu and Y. S. Wang, J. Mater. Chem. C,
2
016, 4, 10329.
2 7
luminescence properties of Sr ScF .
5
6
7
8
B. Wang, H. Lin, F. Huang, J. Xu, H. Chen, Z. B. Lin and Y. S.
Wang, Chem. Mater., 2016, 28, 3515.
Y. H. Yang, D. T. Tu, W. Zheng, Y. S. Liu, P. Huang, E. Ma, R. F.
Li and X. Y. Chen, Nanoscale, 2014, 6, 11098.
B. Zhao, L. Yuan, S. S. Hu, X. M. Zhang, X. J. Zhou, J. F. Tang
and J. Yang, CrystEngComm, 2016, 18, 8044.
W. Y. Yin, L. J. Zhou, Z. J. Gu, G. Tian, S. Jin, L. Yan, X. X. Liu, G.
M. Xing, W. L. Ren, F. Liu, Z. W. Pan and Y. L. Zhao, J. Mater.
Chem, 2012, 22, 6974.
Y. Liu, D. Tu, H. Zhu, E. Ma and X. Y. Chen, Nanoscale, 2013,
5, 1369.
Conclusion
3
+
In conclusion, we have successfully synthesized Sr
Ce, Tb, Eu, Sm, Dy, Er, Tm, Ho and Yb) nanocrystals by one-
step hydrothermal route without employing any surfactants.
2 7
ScF :Ln (Ln
=
3+
Doping Ln with a large ionic radius was beneficial for forming
ultrasmall nanoparticles, which provided a novel method for
controlling the shape and size of other analogous nanocrystals.
9
1
1
0 F. Wang, D. Banerjee, Y. S. Liu, X. Y. Chen and X. S. Liu,
Analyst, 2010, 135, 1839.
2 7
Multiform Sr ScF nano-/microcrystals including nanorods,
quadrangular microplates, cube and polyhedron were
1 Y. J. Huang, H. Y. You, G. Jia, Y. H. Song, Y. H. Zheng, M. Yang,
K. Liu and N. Guo, J. Phys. Chem. C, 2010, 114, 18051.
surfactants. The possible formation mechanisms for the 12 Y. S. Liu, D. T. Tu, H. M. Zhu and X. Y. Chen, Chem. Soc. Rev,
-
synthesized by altering the pH values, F sources and
ultimate shape evolutions from nanorods to other
morphologies (quadrangular microplates, cube and
2013, 42, 6924.
1
1
3 F. Wang, Y. Han, C. S. Lim, Y. Lu, J. Wang, J. Xu, H. Chen, C.
Zhang, M. Hong and X. Liu, Nature ,2010, 463, 1061.
4 B. Y. Chen, B. Dong, J. Wang, S. Zhang, L. Xu, W. Yu and S. W.
Song, Nanoscale, 2013, 5, 8541.
3
+
polyhedron) have been presented in detail. The Sr
2 7
ScF :Ln
(
Ln = Ce, Tb, Eu, Sm, Dy, Er, Tm and Ho) nanocrystals showed
3
+
the characteristic f-f transitions of Ln with emission colors of 15 Y. Sun, X. J. Zhu, J. J. Peng and F. Y. Li, ACS nano, 2013, 7,
11290.
3
bluish violet (Ce , Tm ), green (Tb , Er , Ho ), blue (Dy )
+
3+
3+
3+
3+
3+
3
+
3+
16 W. B. Pei, L. L. Wang, J. S. Wu, B. Chen, W. Wei, R. Lau, L.
Huang and W. Huang, Cryst. Growth Des, 2015, 15, 2988.
7 X. Teng, Y. H. Zhu, W. Wei, S. C. Wang, J. F. Huang, R.
Naccache, W. B. Hu, A. L. Y. Tok, Y. Han, Q. C. Zhang, Q. Y.
Fan, W. Huang, J. A. J Capobianco and L. Huang, J. Am. Chem.
Soc, 2012, 134 , 8340.
18 Y. J. Ding, X. Teng, H. Zhu, L. L. Wang, W. B. Pei, J. J. Zhu, L.
Huang and W. Huang, Nanoscale, 2013, 5, 11928.
9 W. B. Pei, B. Chen, L. L. Wang, J. S. Wu, X. Teng, R. Lau, L.
Huang and W. Huang, Nanoscale, 2015, 7, 4048.
20 X. He and B. Yan, Cryst. Growth Des, 2014, 14, 3257.
and orange (Eu , Sm ) respectively. Under 980 nm excitation,
the blue, green and red UC photoluminescence were achieved
1
3
in the Ln (Ln = Yb, Er, Tm) doped Sr
+
2
ScF
7
nanocrystals, which
3+
1
were attributed to the G
3
→ H
4
6
transition of the Tm , the
3+
2
4
4
4
4
H
11/2/ S3/2→ I15/2 transitions of Er and the
F9/2→ I15/2
3
+
transition of Er
photoluminescence in Sr
chromaticity coordinates of (0.320, 0.330) is firstly obtained.
respectively. The ideal white UC
3
+
3+
3+
2
7
ScF :Yb ,Er ,Tm nanocrystals with
1
3
+
3+
3+
3+
3+
3+
The ET processes of Yb →Er , Yb →Tm and Tm →Er
worked simultaneously originating from two- or three-photon 21 D. G. Li, W. P. Qin, P. Zhang, S. F. Xiao and L. L. Wang,
CrystEngComm, 2016, 18, 6908.
UC processes. The value of Rr/g and the emission intensity were
2
2
2 Y. J. Ding, X. X. Zhang, H. Zhu and J. J. Zhu, J. Mater. Chem. C,
014, 2, 946.
3 M. Pang, X. S. Zhai, J. Feng, S. Y. Song, R. P. Deng, Z. Wang, S.
Yao, X. Ge and H. J. Zhang, Dalton Trans, 2014, 43, 10202.
sensitive to the morphology/size of Sr
modulate the luminescence properties by changing its
morphology/size Because of their simple production process,
2 7
ScF , so we can
2
.
low toxicity, superior stability, small dimension, rich 24 Y. Ai, D. T. Tu, W. Zheng, Y. S. Liu, J. T. Kong, P. Hu, Z. Chen,
M. D. Huang and X. Y. Chen, Nanoscale, 2013, 5, 6430.
luminescence color and ease of mass production, the materials
2
2
2
2
5 M. Pang, J. Feng, S. Y. Song, Z. Wang and H. J. Zhang,
CrystEngComm, 2013, 15, 6901.
6 H. B. Fu, G. X. Yang, S. L. Gai, N. Niu, F. He, J. Xu and P. P.
Yang, Dalton Trans, 2013, 42, 7863.
7 H. L. Qiu, G. Y. Chen, L. Sun, S. W. Hao, G. Han and C. H. Yang,
J. Mater. Chem. 2011, 21, 17202.
8 Q. Huang, J. Yu, E. Ma and K. Lin, J. Phys. Chem. C, 2010, 114,
can be widely applied in the areas of color displays, light,
photonics and biological imaging.
Acknowledgements
This project is financially supported by the National Natural
4719.
Science Foundation of China (51302229), the Fundamental 29 S. J. Zeng, M. K. Tsang, C. F. Chan, K. L. Wong, B. Fei and J. H
Hao, Nanoscale, 2012, 4, 5118.
Research Funds for the Central Universities (XDJK2016C147),
3
3
0 F. Wang, Y. Han, C. S. Lim, Y. H. Lu, J. Wang, J. Xu, H. Y. Chen,
C. Zhang, M. H. Hong and X. G. Liu, Nature, 2010, 463, 1061.
1 F. Zhang, Y. Wan, T. Yu, F. Q. Zhang, Y. F. Shi, S. H. Xie, Y. G.
Li, L. Xu, B. Tu and D. Y. Zhao, Angew. Chem. Int. Ed, 2007,
the Scientific Research Foundation for Returned Scholars,
Ministry of Education of China (46th)
4
6, 7976.
Notes and references
32 S. J. Zeng, M. K. Tsanga, C. F. Chan, K. L. Wong and J. H. Hao,
Biomaterials, 2012, 33, 9232.
1
2
3
H. Lin, J. Xu, Q. M. Huang, B. Wang, H. Chen, Z. B. Lin and Y.
S. Wang, ACS Appl. Mater. Interfaces, 2015, 7, 21835.
Y. Park, K. Lee, Y. Suh and T. Hyeon, Chem. Soc. Rev, 2015,
3
3
3
3 V. Mahalingam, F. Vetrone, R. Naccache, A. Speghini and J. A.
Colloidal Capobianco, Adv. Mater, 2009, 21, 4025.
4 R. Kumar, M. Nyk, T. Y. Ohulchanskyy, C. A. Flask and P. N.
Colloidal Prasad, Adv. Funct. Mater, 2009, 19, 853.
5 Y. L. Dai, D. M. Yang, P. A. Ma, X. J. Kang, X. Zhang, C. X. Li, Z.
Y. Hou, Z. Y. Cheng and J. Lin, Biomaterials, 2012, 33, 8704.
4
4, 1302.
X. Chen, D. Peng, Q. Jua and F. Wang, Chem. Soc. Rev, 2015,
4, 1318.
4
This journal is © The Royal Society of Chemistry 20xx
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Journal Name
3
3
3
6 R. Naccache, F. Vetrone, V. Mahalingam, L. A. Cuccia and J. A. 73 J. Yang, C. M. Zhang, C. Peng, C. X. Li, L. L. Wang, R. T. Chai
C apobianco, Chem. Mater, 2009, 21, 717. and J. Lin, Chem.–Eur. J., 2009, 15, 4649.
7 Q. Liu, Y. Sun, T. S. Yang, W. Feng, C. G. Li and F. Y. Li, J. Am. 74 G. Glaspell, J. Anderson, J. R. Wilkins and M. S. Ei-Shall, J.
Chem. Soc, 2011, 133, 17122. Phys. Chem. C, 2008, 112, 11527.
8 G. C. Jiang, J. Pichaandi, N. J. J. Johnson, R. D. Burke and F. C. 75 Y. P. Li, J. H. Zhang, Y. S. Luo, X. Zhang, Z. D. Hao and X. J.
J. M. van Veggel, Langmuir, 2012, 28, 3239.
Wang, J. Mater. Chem., 2011, 21, 2895.
76 B. Dong, H. W. Song, H. Q. Yu, H. Zhang, R. F. Qin, X. Bai, G.
H. Pan, S. Z. Lu, F. Wang and L. B. Fan, J. Phys. Chem., 2008,
112, 1435.
3
4
9 H. S. Jang, K. Woo and K. Lim, Opt. Express, 2012, 20, 17107.
0 T. Yang, Y. Sun, Q. Liu, W. Feng, P. Yang and F. Li,
Biomaterials, 2012, 33, 3733.
4
4
4
4
1 S. L. Gai, G. X. Yang, X. B. Li, C. X. Li, Y. L. Dai, F. He and P. P. 77 X. Ye, J. E. Collins, Y. Kang, J. Chen, D. T. N. Chen, A. G. Yodh
Yang, Dalton Trans., 2012, 41, 11716.
and C. B. Murray, Proc. Natl. Acad. Sci. U. S. A., 2010, 107,
22430.
2 D. Yang, Y. Dai, P. Ma, X. Kang, Z. Cheng, C. Li and J. Lin,
Chem.–Eur. J., 2013, 19, 2685.
3 D. Yang, X. Kang, P. Ma, Y. Dai, Z. Hou, Z. Cheng, C. Li and J.
Lin, Biomaterials, 2013, 34, 1601.
78 H. Na, K. Woo, K. Lim and H. S. Jang, Nanoscale, 2013, 5,
4242.
4 Q. Ju, T. Tu, Y. S. Liu, R. F. Li, H. M. Zhu, J. C. Chen, Z. Chen,
M. D. Huang and X. Y. Chen, J. Am. Chem. Soc.,2012, 134,
1
323.
4
4
5 X. He and B. Yan, J. Mater. Chem. C, 2014, 2, 2368.
6 L. Zhou, S. S. Hu, X. J. Zhou, J. F. Tang, J. Yang,
CrystEngComm, 2016, 18, 7590.
4
7 Z. Wang, J. Hao and H. L. W. Chan, J. Mater. Chem.,2010, 20,
3
178.
4
4
5
5
8 D. Q. Chen and Y. S. Wang, Nanoscale, 2013, 5, 4621.
9 J. H. Hao and M. Cocivera, Appl. Phys. Lett., 2002, 81, 4154.
0 F. Wang and X. G. Liu, Chem. Soc. Rev., 2009, 38, 976.
1 D. Q. Chen, Y. L. Yu, F. Huang, P. Huang, A. P. Yang and Y. S.
Wang, J. Am. Chem. Soc., 2010, 132, 9976.
5
5
5
5
2 F. Wang, Y. Han, C. S. Lim, Y. H. Lu, J. Wang, J. Xu, H. Y. Chen,
C. Zhang, M. H. Hong and X. G. Liu, Nature, 2010, 463, 1061.
3 L. L. Han, Y. H. Wang, L. N. Guo, L. Zhao and Y. Tao,
Nanoscale, 2014, 6, 5907.
4 G. F. Wang, Q. Peng and Y. D. Li J. Am. Chem. Soc. 2009,131,
1
4200.
5 Y. S. Liu, D. T. Tu, H. M. Zhu, R. F. Li, W. Q. Luo and X. Y. Chen,
Adv. Mater., 2010, 22, 3266.
5
5
6 F. Wang and X. G. Liu, J. Am. Chem. Soc., 2008, 130, 5642.
7 K. Z. Zheng, D. S. Zhang, D. Zhao, N. Liu, F. Shi and W. P. Qin,
Phys. Chem. Chem. Phys., 2010, 12, 7620.
5
8 J. W. Wang and P. A. Tanner, J. Am. Chem. Soc., 2010, 132,
9
9 D. Matsuura, Appl. Phys. Lett. 2002, 81, 4526.
0 D. Q. Chen, Y. S. Wang, K. L. Zheng, T. L. Guo, Y. L. Yu and P.
Huang, Phys. Lett., 2007, 91, 1903.
47.
5
6
6
1 G. G. Li, M. M. Shang, D. L. Geng, D. M. Yang, C. Peng, Z. Y.
Cheng and J. Lin, CrystEngComm, 2012, 14, 2100.
2 D. Q. Chen and Y. S. Wang, Nanoscale, 2013, 5, 4621.
3 D. Y. Chen, Y. L. Yu, F. Huang, A. P. Yang and Y. S. Wang, J.
Mater. Chem., 2011, 21, 6186.
6
6
6
4 Y. Tian, R. N. Hua, B. J. Chen, N. S. Yu, W. Zhang and L. Y. Na,
CrystEngComm, 2012, 14, 8110.
6
6
5 X. Wang and Y. D. Li Angew. Chem., Int. Ed. 2002, 41 4790.
6 C. M. Zhang, C. X. Li, C. Peng, R. T. Chai, S. S. Huang, D. M.
Yang, Z. Y. Cheng and J. Lin, Chem.-Eur. J. 2010, 16, 5672.
7 C. X. Li, Z. W. Quan, P. P. Yang, S. S. Huang, H. Z. Lian and J.
Lin, J. Phys. Chem. C, 2008, 112, 13395.
6
6
8 Y. Tian, B. J. Chen, R. N. Hua, N. S. Yu, B. Q. Liu, J. S. Sun, L. H.
Cheng, H. Y. Zhong, X. P. Li and J. S. Zhang, CrystEngComm,
2
012, 14, 1760.
6
7
7
7
9 H. N. Luitel, R. Chand, T. Torikai, M. Yada and T. Watari, RSC
Adv., 2015, 5, 17034.
0 Z. H. Xu, X. J. Kang, C. X. Li, Z. Y. Hou, C. M. Zhang, D. M.
Yang, G. G. Li and J. Lin, Inorg. Chem., 2010, 49, 6706.
1 B. Zhao, L. Yuan, S. S. Hu, X. M. Zhang, X. J. Zhou, J. F. Tang
and J. Yang, New J. Chem., 2016, 40, 9211.
2 C. M. Zhang, P. A. Ma, C. X. Li, G. G. Li, S. S. Huang, D. M.
Yang, M. M. Shang, X. J. Kang and J. Lin, J. Mater. Chem.,
2
011, 21, 717.
1
2 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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DOI: 10.1039/C6TC05477C
TOC
Sr
2 7
ScF micro/nanocrystals with various morphologies were firstly synthesized via a
3
+
3+
3+
one-step surfactant-free hydrothermal route. Sr ScF :Yb /Er /Tm phosphors show
2
7
tunable RGB and white emissions.