Na(Y1.5Na0.5)F6:RE3+(Dy3+,Tb3+,Eu3+,Tm3+,Ho3+):Controllable morphology, multicolor light and thermal properties

Article abstract of DOI:10.1016/j.jallcom.2020.157833

A series of emission-tunable Na(Y_1.5Na_0.5)F₆: RE³⁺ (Dy³⁺,Tb³⁺, Eu³⁺, Tm³⁺, Ho³⁺) phosphors were firstly synthesized by the glycine assisted one-step hydrothermal process. The structure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that the samples contain YF₃ and Na(Y_1.5Na_0.5)F₆ phases, and the size and shape of the products could be tuned just by adjusting the pH values of the initial reaction solutions or by adjusting the RE³⁺/NaF ratio or RE³⁺/NaBF₄ ratio. The product morphologies include spindle-like microstructures, six prismatic, irregular microrods, micron hexagonal prisms and nano-spheres, micron elliptical disc, flower-like microstructures, spindle-like structures and irregular bulk. Furthermore, the photoluminescence properties of Na(Y_1.5Na_0.5)F₆: RE³⁺ (Dy³⁺, Tb³⁺, Eu³⁺, Tm³⁺, Ho³⁺) were investigated in detail. Additionally, the emission color of Na(Y_1.5Na_0.5)F₆: RE³⁺ (Dy³⁺, Tb³⁺, Eu³⁺, Tm³⁺, Ho³⁺) can be turned by adjusting the amount and kind of RE³⁺ ions. Importantly, the temperature-dependent photoluminescence of as-prepared phosphors was evaluated in detail. All these properties indicate that the developed phosphors may potentially be used as single-component multicolor-emitting phosphors.

Full text of DOI:10.1016/j.jallcom.2020.157833

Journal of Alloys and Compounds xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Na(Y1.5Na0.5)F6:RE3þ(Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ):Controllable
morphology, multicolor light and thermal properties
,
Hongxia Guan a *, Yunfei Li b
a Changchun Institute of Technology, Changchun, Jilin, 130012, China
b College of Humanities &Information Changchun University of Technology, Changchun, Jilin, 130122, China
a r t i c l e i n f o
a b s t r a c t
A series of emission-tunable Na(Y1.5Na0.5)F6: RE3þ (Dy3þ,Tb3þ, Eu3þ, Tm3þ, Ho3þ) phosphors were firstly
synthesized by the glycine assisted one-step hydrothermal process. The structure and morphology were
characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed
that the samples contain YF3 and Na(Y1.5Na0.5)F6 phases, and the size and shape of the products could be
tuned just by adjusting the pH values of the initial reaction solutions or by adjusting the RE3þ/NaF ratio
or RE3þ/NaBF4 ratio. The product morphologies include spindle-like microstructures, six prismatic,
irregular microrods, micron hexagonal prisms and nano-spheres, micron elliptical disc, flower-like mi-
crostructures, spindle-like structures and irregular bulk. Furthermore, the photoluminescence properties
of Na(Y1.5Na0.5)F6: RE3þ (Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ) were investigated in detail. Additionally, the
emission color of Na(Y1.5Na0.5)F6: RE3þ (Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ) can be turned by adjusting the
amount and kind of RE3þ ions. Importantly, the temperature-dependent photoluminescence of as-
prepared phosphors was evaluated in detail. All these properties indicate that the developed phos-
phors may potentially be used as single-component multicolor-emitting phosphors.
Article history:
Received 12 May 2020
Received in revised form
14 October 2020
Accepted 2 November 2020
Available online xxx
Keywords:
Morphology control
Multicolor light
Thermal properties
© 2020 Elsevier B.V. All rights reserved.
2. Introduction
method.The template method is mainly used to synthesize nano-
wires, nanoribbons, nanofilaments, nanotubes and sheet nano-
Lanthanide-doped luminescent materials have gained consid-
erable attention due to their specific electronic, optical, magnetic
and catalytic properties [1e5]. Among different luminescent ma-
terials, the very low phonon energy of Na(Y1.5Na0.5)F6 makes multi-
phonon relaxation inefficient in this host crystal, and so that
luminescence intensity of the trivalent rare-earth ions increases,
compared with that in oxide laser crystals [6e8]. Hence,
Na(Y1.5Na0.5)F6 is a good matrix.
Size and shape are also key parameters for chemical and phys-
ical characteristics, and numerous studies and efforts were aimed
to control the size, phase, shape, and dimensionality of nanometer/
micron materials [9e12]. At present, many methods have been
reported in the literature to synthesize nanometer/micron mate-
rials, such as molten-salt synthesis, hydrothermal processing,
template synthesis, microwave method, coprecipitation method
and so on [13e19]. The molten salt method has a high requirement
on the co-solvent, which imposes some limitations on this
materials. The reproducibility of the morphology of materials
synthesized by microwave method is generally poor. Although the
method of co-precipitation is simple, the morphology of the syn-
thesized material is relatively simple. The hydrothermal treatment
is relatively mild, simple, and easy for obtaining a range of products.
The size of nano/micron material can be controlled by changing the
type of fluorine source, adjusting the dosage of fluorine source and
adjusting the pH value of solution. Hitherto, in this work, we syn-
thesize and study Na(Y1.5Na0.5)F6 materials of different morphology
by a facile hydrothermal process using nitric acid or ammonium
hydroxide for adjusting the pH value.
One of the strategies for generating multicolor light from single-
phased phosphors is co-doping or tr-doping of different rare earth
4
ions [20e22]. The Dy3þ ions emit yellow light due to the F9/
/
6H13/2 transition [23,24]. The Tb3þ ions exhibit two charac-
2
teristic emission bands ascribed to the 5D4
/ /
7F6 and 5D4 7F5
transition [25,26]. The Tm3þ ions emit intense blue light at 449 nm
[27,28]. As one of the most frequently used red emitters in rare
earth ions doped materials, Eu3þ mainly presents high efficiency,
characteristic intense red emissions peaks at around 616 nm
* Corresponding author.
E-mail address: guanhx18@126.com (H. Guan).
https://doi.org/10.1016/j.jallcom.2020.157833
0925-8388/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: H. Guan and Y. Li, Na(Y1.5Na0.5)F6:RE3þ(Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ):Controllable morphology, multicolor light and
thermal properties, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2020.157833

H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
[29e32]. The Ho3þ ions possesses a wealth of energy levels and,
consequently, they have many luminescent states due to the
complexity of the 4f10 energy level system [33,34]. So, the multi-
color and white light can be realized by co-doped or tri-doped rare
earth ions (Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ) in phosphors.
In the present work, to prepare single-phased multicolor-
emitting phosphors, Na(Y1.5Na0.5)F6 was used as the host and rare
earth ions of Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ were co-doped or tri-
doped. In addition, the products with diverse morphologies and
sizes were successfully synthesized by changing the type of fluorine
source, adjusting the dosage of fluorine source and pH value of
solution.
stirred for another 20 min. Third, using the nitric acid or ammonia,
the pH value of the solution was adjusted. Then, the resultant milky
colloidal suspension was transferred to a 50 mL stainless Teflon-
loined autoclave, sealed, and kept at 180 ꢁC for 24 h. Finally, the
autoclave was naturally cooled to room-temperature and the
products were deposited at the bottom of the vessel. The pre-
cipitates were separated by centrifugation, washed with deionized
water and ethanol in sequence each several times to remove citric
acid and other remnants, and then dried at 60 ꢁC for 12 h in the air.
Other samples were prepared by similar procedures, except for
2. Experimental
2.1. Materials
All the chemicals were used directly as received without further
purification. Y(NO3)3, Dy(NO3)3, Tb(NO3)3, Eu(NO3)3,Tm(NO3)3 and
Ho(NO3)3 were prepared by dissolving the corresponding Y2O3(A.R.
Shandong Desheng), Dy2O3, Tb4O7 (A.R. Shandong Desheng),
Eu2O3(A.R. Shandong Desheng), Tm2O3 (A.R. Shandong Desheng)
and Ho2O3(A.R. Shandong Desheng) in HNO3 solution at elevated
temperature followed by evaporating superfluous HNO3. NaBF4
(A.R. Beijing Chemical Works) and NaF (A.R. Beijing Chemical
Works) were of analytical grade and were purchased from Beijing
Chemical Corporation.
2.2. Preparation
A series of rare earth-doped Na(Y1.5Na0.5)F6 samples were syn-
thesized by glycine acid assisted hydrothermal process without
further sintering treatment. In a typical procedure of preparing
representative Na(Y1.5Na0.5)F6: 2%Dy3þ, 1%Tb3þ compound: First,
19.4 mL Y(NO3)3 (0.1 M), 0.8 mL Dy(NO3)3 (0.05 M) and
0.4 mL Tb(NO3)3 (0.05 M) were poured to a 100 mL flask with
0.6006 g (1:4 M ratio for RE3þ/glycine) of glycine (hereinafter
shortened form Glyꢀ). The solution was stirred for 20 min. Second,
1.0078 g of NaF (1:12 M ratio for RE (NO3)3/NaF) was slowly added
into the above solution. Then the above solution is continuously
Fig. 2. SEM images of samples prepared with glycine at different RE3þ/NaF ratio:
1:1(a), 1:3 (b), 1:5 (c), 1:7 (d), 1:9 (e), 1:11 (f),1:12 (g); XRD patterns of samples pre-
pared with glycine acid at different RE3þ/NaF ratio (h); The corresponding standard
data of YF3 (JCPDS No. 70e1935) and Na(Y1.5Na0.5)F6 (JCPDS No. 16e0334) are given as
reference.
Fig. 1. XRD patterns of Na(Y1.5Na0.5)F6 and Na(Y1.5Na0.5)F6:RE3þ(RE ¼ Dy, Tb, Eu, Tm,
Ho) samples (1:12 M ratio for RE (NO3)3/NaF); The corresponding standard data of
Na(Y1.5Na0.5)F6 (JCPDS No. 16e0334) is given as reference；.
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H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
changing the value of the NaBF4, NaF, RE (NO3)3 and pH level.
standard values of PDF card (JCPDS No. 16e0334) indicating that
the original host structure is persistent on doping Dy3þ, Tb3þ, Eu3þ
,
Tm3þ, Ho3þ ions. This result indicates that the completely crystal-
line and pure-phase Na(Y1.5Na0.5)F6 can be obtained by a one-step
hydrothermal method and the Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ ions
are completely incorporated into the Na(Y1.5Na0.5)F6 host lattice
without making significant changes to the crystal structure.
Moreover, the sharp and strong peaks indicate that the products
synthesized at low temperatures are still highly crystalline.
2.3. Characterization
The morphology and size of the samples were observed by a
field emission electron microscope (FESEM, S-4800, Hitachi, Japan).
X-ray powder diffraction (XRD) data for the prepared samples
(Na(Y1.5Na0.5)F6: Dy3þ, Tb3þ, Eu3þ, Tm3þ, Ho3þ) were taken using a
Rigaku D/max-RA X-ray diffractometer with Cu K
a radiation
(
l
¼ 0.15406 nm) and Ni filter, operating at 20 mA, 30 kV, scanning
speed, step length and diffraction range were 10ꢁ/min, 0.1ꢁ and
20e70ꢁ, respectively. The measurements of photoluminescence
(PL) and photoluminescence excitation (PLE) spectra were carried
out by a Jobin Yvon FluoroMax-4 using a 150 W xenon lamp as the
excitation source. The excitation and emission slits were set to 2.5
and 2.5 nm.
3.2. Morphology and structure
The RE3þ/NaF ratio is found to be an important synthetic
parameter to influence the shape and microstructure of particles.
The SEM images of samples prepared with glycine at different RE3þ
/
NaF ratio are shown in Fig. 2. When RE3þ/NaF ¼ 1:1 was introduced
into the reaction system, the uniform spindle-like structures with
sheaf in the middle part are obtained. As the RE3þ/NaF ration is
increased to 1:3, although similar spindle-like structures can be
obtained, the sheaf in the middle part disappears. The spindle-like
3. Results and discussion
3.1. Crystallization behavior and structure
structures become irregular aggregated. With increasing the RE3þ
/
The XRD patterns of Na(Y1.5Na0.5)F6 phosphors together with
the theoretical pattern calculated on the base of PDF card (JCPDS
No. 16e0334) [35] are given in Fig. 1. They match well with the
NaF ratio to 1:5, the morphology of the sample becomes six pris-
matic and irregular nanoparticles. As the RE3þ: NaF ratio continuing
to increase to1:7, 1:9, 1:11, 1:12, the irregular nanoparticles almost
Fig. 3. SEM images of the synthesized samples with glycine (1:12 M ratio for RE (NO3)3/NaF)at the different pH values of the initial solution: pH ¼ 1.69 (a), pH ¼ 2.26 (b), pH ¼ 3.51
(c), pH ¼ 4.34 (d), pH ¼ 5.43 (e), pH ¼ 6.15 (f), pH ¼ 7.55 (g), pH ¼ 8.12 (h), pH ¼ 9.32 (i), pH ¼ 10.10 (j) and pH ¼ 11.10(k); XRD patterns of the synthesized samples (1:12 M ratio for
RE (NO3)3/NaF) at the different pH values of the initial solution (l, m); The corresponding standard data of YF3 (JCPDS No. 70e1935), NaYF4 (JCPDS No. 77e2042) and Na(Y1.5Na0.5)F6
(JCPDS No. 16e0334) are given as reference.
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H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
entirely disappear, and the morphology of the sample develop to
irregular microrods. The results reveal that the RE3þ: NaF ratio
plays a key role in the shapes and sizes of the as-prepared samples.
The XRD patterns of samples at different RE3þ/NaF ratio are pre-
sented in Fig. 2h. It can be seen that, when the RE3þ/NaF ratio is 1:1,
the XRD pattern shows that the product is composed of mixed of
YF3 and Na(Y1.5Na0.5)F6 crystal phases. With the RE3þ/NaF ratio
increase to 1:3, the resulted product could be indexed as a pure
orthorhombic phase YF3. By further increasing the RE3þ/NaF ratio
to 1:5, it is obvious that the products composed of mixed crystal
phases of YF3 and Na(Y1.5Na0.5)F6. However, as the RE3þ/NaF ratio
continuously increase to 1:7, 1:9, 1:11, 1:12, all the products could
be clearly indexed to the pure orthorhombic phase Na(Y1.5Na0.5)F6
crystal. Thus, we can reasonably infer that the amount of NaF plays
an important role in the crystallization process.
In the synthesis of inorganic nano/microcrystals, the pH value of
initial solution could be employed to modify certain crystallo-
graphic surfaces of samples. The SEM images of the products syn-
thesized at different pH values and NaF as F- source are shown in
Fig. 3. As seen in Fig. 3a, for the sample prepared at pH ¼ 1.69, some
micron sized hexagonal prisms and nano-spheres are formed. In
the case of at pH ¼ 2.26, although similar micron sized hexagonal
prisms and nano-spheres can be obtained, a number of nano-
spheres obviously decreases (Fig. 3b). If we adjust an acid circum-
stance for the reaction (pH 3.51), then the morphology of the
micron hexagonal prisms transforms in a nonobvious manner; only
the nano-spheres disappeared, as shown in Fig. 3c. With the pH
value increase to 4.34, the morphology still remains micron hex-
agonal prisms, but their length obviously decreases. Adjusting the
solution pH values at 5.43e11.10, the morphology become to
micron rods, which have an uneven surface. The results show that
the pH value of initial solution can influence the morphology of
products. The XRD patterns of samples prepared at different pH
values are given in Fig. 3l and m. When the pH value is adjusted
1.69, the XRD pattern shows that the product is composed of YF3
(JCPDS No. 70e1935) [35] and NaYF4 (JCPDS No. 77e2042) [36].
With the pH value increase to 2.26, the resulted product could be
indexed as NaYF4 (JCPDS No. 77e2042) and Na(Y1.5Na0.5)F6 (JCPDS
No. 16e0334). As the pH value continuously increase to 3.51e11.10,
all the diffraction peaks can be assigned to a pure hexagonal
Na(Y1.5Na0.5)F6 phase. The results indicate that, with the increase in
pH value of initial solution, the phase composition of the sample
shifted to a pure hexagonal Na(Y1.5Na0.5)F6 phase.
The effect of NaBF4 on the product morphology is investigated,
as displayed in Fig. 4. In Fig. 4a, the sample prepared at RE3þ: NaBF4
ratio ¼ 1:1, the product consists of uneven micron elliptical disc
with diameter about 2.7 mm. Additionally, Fig. 4a clearly shows that
uneven micron elliptical disc is composed of many rhombus
nanoparticles. For the sample prepared at RE3þ: NaBF4 ratio ¼ 1:3,
the flower-like microstructures composed of a conjunction of
rhombus nanoparticles can be observed. In the case of the sample
prepared at RE3þ: NaBF4 ratio ¼ 1:5, the morphology is converted
to spindle-like structures with sheaf in the middle part and flower-
like microstructures. When the ratio are RE3þ: NaBF4 ratio ¼ 1:6
and RE3þ: NaBF4 ratio ¼ 1:7, the particles are shaped as spindle-like
structures with sheaf in the middle part, and the flower-like mi-
crostructures disappear. With the RE3þ: NaBF4 ratio increases to
1:9, the spindle-like structures split to irregular bulk in part. As the
RE3þ: NaBF4 ratio is controlled at 1:11, the morphology becomes
completely irregular. Adjusting the RE3þ: NaBF4 ratio to 1:12, the
morphology grows into irregular big bulks. The results reveal that
the RE3þ: NaBF4 ratio plays a key role in the shapes and sizes of the
as-prepared samples. From Fig. 4 g, it can be seen that only the pure
YF3 is obtained.
Fig. 4. SEM images of samples prepared with glycine at different RE3þ/NaBF4 ratio:
1:1(a), 1:3 (b), 1:5 (c), 1:6 (d), 1:7 (e), 1:9 (f), 1:11 (g), 1:12 (h); XRD patterns of samples
prepared with glycine acid at different RE3þ/NaBF4 ratio (i). The corresponding stan-
dard data of YF3 (JCPDS No. 70e1935) are given as reference.
based system not only depends on the intrinsic structure of the
target compounds but also requires more fastidious control of the
growth parameters. Thus, the SEM images of samples prepared
with the use of NaBF4 as Fꢀ source and different pH values were
shown in Fig. 5. As evident in Fig. 5a, in the sample prepared at
pH ¼ 1.26, some walnut-like shapes appear. In the case of the
sample prepared at pH ¼ 2.83, the prepared samples grow into
bulk. If we adjust an acid condition for the reaction (pH 3.88), then
the bulk morphology transforms in a nonobvious manner, but some
Generally, the successful synthesis of materials in a solution-
4

H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
micron hexagonal prisms appeared, as shown in Fig. 5c. With the
pH values of 4.39e9.93, the morphology still remains micron
hexagonal prisms and bulk, but the bulk particles gradually
decrease. At pH ¼ 10.23e12.15, the micron rods with uneven sur-
face are formed. The results show that the pH value of initial so-
lution can influence the morphology of products. Fig. 5(m, n) shows
the XRD patterns of samples at different pH values. When the pH
value is adjusted to 1.26 and 2.83, the XRD patterns show that the
products are composed of YF3 (JCPDS No. 70e1935) [36]. With the
pH value increase to 3.88e9.33, the resulted product could be
indexed as YF3 (JCPDS No. 70e1935) and Na(Y1.5Na0.5)F6 (JCPDS No.
16e0334). As the pH value continuously increases to 10.23e12.15,
all the diffraction peaks can be assigned to a pure hexagonal
Na(Y1.5Na0.5)F6 phase. The results show that, with the increase in
the pH value of initial solution, the phase composition of the
sample shifted to a pure hexagonal Na(Y1.5Na0.5)F6 phase.
3.3. Luminescent properties of Na(Y1.5Na0.5)F6:
Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ
As shown in Fig. 6a the excitation spectrum of the Na(Y1.5Na0.5
)
F6:2%Dy3þ product monitored at 570 nm includes several bands
centered at 293, 324, 337, 348, 363, 384, 425, 451 and 472 nm,
corresponding to the transitions of Dy3þ from 6H15/2 to 4H13/2,6P3/2
,
4
4F5/2
,
4P7/2
,
6P5/2
,
4F7/2
,
4G11/2
,
4I15/2 and F9/2, respectively. As
depicted in Fig. 6b, The excitation spectrum of the Na(Y1.5Na0.5
)
F63%Tb3þ product monitored at 542 is made up of a series of sharp
peaks at 317, 340, 352, 359, 368, 378 and 486 nm, which can be
Fig. 5. SEM images of the synthesized samples with glycine (1:12 M ratio for RE (NO3)3/NaBF4) at the different pH values of the initial solution: pH ¼ 1.26 (a), pH ¼ 2.83 (b),
pH ¼ 3.88 (c), pH ¼ 4.39 (d), pH ¼ 5.83 (e), pH ¼ 6.23 (f), pH ¼ 7.25 (g), pH ¼ 8.41 (h), pH ¼ 9.33 (i), pH ¼ 10.23 (j), pH ¼ 11.27(k) and pH ¼ 12.15(l); XRD patterns of the synthesized
samples (1:12 M ratio for RE (NO3)3/NaBF4) at the different pH values of the initial solution (m, n); The corresponding standard data of YF3 (JCPDS No. 70e1935) and Na(Y1.5Na0.5)F6
(JCPDS No. 16e0334) are given as reference.
5

Fig. 6. Series of photoluminescence emission spectra of (a)Na(Y1.5Na0.5)F6:2%Dy3þ and (b)Na(Y1.5Na0.5)F6:3%Tb3þ and (c)Na(Y1.5Na0.5)F6:1%Tm3þ
.
ascribed to 7F6/5D0, 7F6/5G2, 7F6/5D2, 7F6/5G5, 7F6/5G6,
7F6/5D3 and 7F6/5D4. The excitation spectrum of Na(Y1.5Na0.5
)
F6:1%Tm3þ which were monitored at 449 nm have the fef transi-
tion of 3H6 /1D2 of Tm3þ at 356 nm.
In this work, we focus on investigating the down conversion
luminescence of Na(Y1.5Na0.5)F6: Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ syn-
thesized at pH ~ 8 with NaF as F source. The PL spectra for the
prepared phosphor Na(Y1.5Na0.5)F6:2%Dy3þ, x%Tb3þ (x ¼ 0, 1, 2, 3)
samples under the 348 nm excitation are shown in Fig. 7a. In the
emission spectrum of Na(Y1.5Na0.5)F6:2%Dy3þ, x%Tb3þ(x ¼ 0, 1, 2, 3)
(Fig. 7a), five primary bands appear in the blue, green, yellow, or-
ange red, red emission region peaking at 486, 542, 570, 618 and
664 nm, which are assigned to the Dy3þ of 4F9/2 / 4H15/2 (486 nm),
4
4F9/2
/
4H13/2 (570 nm), F9/2
/
4H11/2 (664 nm) transitions and
the Tb3þ of 5D4/7F5 (542 nm), 5D4/7F3 (618 nm) transitions,
respectively. More importantly, the relative luminescence in-
tensities of three emission peaks of Dy3þ and two emission peaks of
Tb3þ vary with the alteration of x, as shown in Fig. 7b. Therefore, the
emitting color of the products can easily be tuned.
The down conversion luminescence properties of Tb3þ and Eu3þ
co-doped Na(Y1.5Na0.5)F6 with different Eu3þ concentrations are
also investigated and the spectra are shown in Fig. 8. From the
down conversion emission spectra of Na(Y1.5Na0.5)F6: 3%Tb3þ, y%
Eu3þ (y ¼ 1, 2, 3, 5, 6), the strong blue, green and yellow emission
bands centered at 488, 542, 586 nm as well as the orange red, red
emission bands centered at 591, 614, 694 nm can be observed
(Fig. 8a). The six emission bands can be assigned to the 5D4/7F6
(488 nm), 5D4/7F5 (542 nm), 5D4/7F4 (586 nm) transitions of the
Tb3þ ions and the 5D0/7F1 (591 nm), 5D0/7F2 (616 nm) and
5D0/7F4 (694 nm) transitions of the Eu3þ ions, respectively. More
importantly, the relative luminescence intensities of three emission
peaks of Tb3þ and three emission peaks of Eu3þ vary with the
alteration of y, as shown in Fig. 8b. Therefore, the emitting color of
the products can easily be tuned.
The fluorescent decay curves of Tb3þ ions emission in the
Na(Y1.5Na0.5)F6: 3%Tb3þ, y%Eu3þ samples under monitored at
542 nm with irradiation of 368 nm were measured. From Fig. 8c,
Fig. 7. (a) Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6:2%Dy3þ, x%
Tb3þ (x ¼ 0,1,2,3) with different Tb3þ doped concentrations (lex ¼ 348 nm); (b)
Dependence of the emission intensity on the Tb3þ concentrations.
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H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
determined to be 4.591, 4.061, 3.696, 3.369, 3.139, 2.963 and
2.742 ms, respectively. The lifetimes for Tb3þ ions were found to
drastically decrease with increasing the Eu3þ concentration.
The emission spectra of Na(Y1.5Na0.5)F6: 3%Dy3þ
,
m%
Eu3þ(m ¼ 0，1, 2, 3, 4, 5, 6, 7) recorded under excitation by 384 nm
are presented in Fig. 9. The emission peaks at 481 nm (5F9/2 / 6H15/
2) and 570 nm (5F9/2
/
6H13/2) from Dy3þ, as well as at 591 nm
(5D0/7F1), 614 nm (5D0-7F2), 697 nm (5D0-7F4) from Eu3þ are
shown in Fig. 9a. In Fig. 9b, one can see that with the increase of m
value, the Eu3þ related orange red and red emissions are enhanced,
whereas the blue and yellow emission intensities of the Dy3þ ions
decrease. With the change of doping rare earth ions concentrations,
the emission intensity of Dy3þ and Eu3þ also change. Thereby, the
different tone of yellow can be obtained.
The photoluminescence spectra of Tm3þ
,
Dy3þ co-doped
Na(Y1.5Na0.5)F6 phosphors are presented in Fig. 10. The character-
istic emission peaks of the Tm3þ and Dy3þ are observed under the
most efficient excitation at 356 nm. The blue，yellow-green and
red emissions centered at 480, 572 and 658 nm originate, respec-
4
4
tively, from the F9/2
/ , / /
6H15/2 4F9/2 6H13/2 and F9/2 6H11/2
transitions of Dy3þ ions. The characteristic green emission peaks at
449 nm are ascribed to the transitions of 1D2/3F4 of Tm3þ ions. As
shown in Fig. 9b, the PL intensity of Dy3þ ions first increase and
then decrease, whereas the PL intensity of Tm3þ ions decrease-
monotonically with the Dy3þ concentration increase. Therefore, the
emitting color of the products can easily be tuned.
The PL emission spectra of Na(Y1.5Na0.5)F6:3%Tm3þ, z%Ho3þ
(z ¼ 0.5, 1, 1.5, 2) samples excited at 356 nm with varied concen-
tration of Ho3þ ions are given in Fig.11. In Fig.11a, it can be observed
that all the samples present two groups of emission bands in blue
and green regions related to the electronic transitions 1D2/3F4 of
Tm3þ and 5F3/5I8 and5F4/5I8 of Ho3þ, respectively. When the
concentration of Tm3þ is 1%, the emission intensity of Ho3þ ions
first increases and then decreases, and that of Tm3þ ions decreases
with the Ho3þ ions concentration increasing. With the change of
doping rare earth ions concentrations, the emission intensity of
Tm3þ and Ho3þ also change. Thereby, the different tone of blue is
expected to obtained.
The aim of this study is to realize tunable color emission,
including white light, in a single-phase host. For this purpose, the
appropriate combined luminescent ions Dy3þ, Tb3þ, and Eu3þ as
emitters of blue, green, and red light in tri-doped Na(Y1.5Na0.5)F6
host were selected for tunable color generation, including white
light. Thereby, a series of PL spectra of Na(Y1.5Na0.5)F6: 5%Dy3þ,2%
Dy3þ,g%Eu3þ(g ¼ 1, 2, 3, 4, 5) were recorded. In Fig. 12a, the typical
emissions lines of Dy3þ, Tb3þ and Eu3þ ions can be observed. The
emission intensities of Dy3þ and Tb3þ are obviously strong; How-
ever, when the Eu3þ ions are introduced into the system, there is a
significant decrease in the emission intensities of Dy3þ and Tb3þ. As
Eu3þ content increases, the emission intensity of Dy3þ and Tb3þ
gradually decrease, whereas the emission intensity of Eu3þ in-
creases. The results clearly display that multicolored luminescence
can be obtained in the Na(Y1.5Na0.5)F6 system by adjusting the
concentration of Eu3þ ions.
As it is known, color can be represented by the Commission
Internationale de L’Eclairage (CIE) 1931 chromaticity coordinates,
and, so, the CIE chromaticity diagram of Na(Y1.5Na0.5)F6:
Dy3þ,Tb3þ,Eu3þ phosphors is provided in Fig. 13. The related CIE
coordinates are listed in Table 1. For Na(Y1.5Na0.5)F6: Dy3þ,Tb3þ, the
emitting color can be easily tuned from the white to the light yel-
low, as show in Fig. 13(A points 1e3). In Fig. 13(A points 4e9), one
can see that, with increasing of the Eu3þ concentrations, the color
tone of Na(Y1.5Na0.5)F6: Tb3þ, Eu3þ changes from yellow green
through yellow to orange red. As observed in Fig. 13(A points
10e14), the luminescence color can be tuned from blue to light blue
Fig. 8. Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6:3%Tb3þ,y%Eu3þ
(y ¼ 1, 2, 3, 5, 6)with different Eu3þ doped concentrations (lex ¼ 368 nm); (b)
Dependence of the emission intensity on the Eu3þ concentrations. (c) Decay curves for
Tb3þ ions in Na(Y1.5Na0.5)F6: 3%Tb3þ,y%Eu3þsamples (excited at 368 nm, monitored at
542 nm).
one can see that all the luminescent decay times of Tb3þ in
Na(Y1.5Na0.5)F6: 3%Tb3þ, y%Eu3þ can be fitted well with a single
exponential function as
t
I ¼ I0 þ Aeꢀt=
(1)
Where I and I0 are the luminescence intensities at times t and 0,
respectively, and is the luminescence life time. As shown in
Fig. 8c, the corresponding luminescence decay times are
t
7

H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 9. Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6:3%Dy3þ,m%
Eu3þ(m ¼ 1, 2, 3, 4, 5, 6, 7) with different Eu3þ doped concentrations (lex ¼ 384 nm);
(b) Dependence of the emission intensity on the Eu3þ concentrations.
Fig. 11. Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6:3%Tm3þ, z%
Ho3þ(z ¼ 0.5, 1,1.5, 2) with different Ho3þ doped concentrations (lex ¼ 356 nm); (b)
Dependence of the emission intensity on the Ho3þ concentrations.
Fig. 12. Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6: 5%Dy3þ,2%
Dy3þ,g%Eu3þ(g ¼ 1, 2, 3, 4, 5) with different Eu3þ doped concentrations (lex ¼ 360 nm);
(b) Dependence of the emission intensity on the Eu3þ concentrations.
Fig. 10. Series of photoluminescence emission spectra of Na(Y1.5Na0.5)F6:1%Tm3þ,n%
Dy3þ (n ¼ 0.5, 1, 2,3 4, 5) with different Dy3þ doped concentrations (lex ¼ 356 nm); (b)
Dependence of the emission intensity on the Tb3þ concentrations.
8

H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 13. CIE chromaticity diagram (A, B) of Na(Y1.5Na0.5)F6:Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ phosphors.
Table 1
The CIE chromaticity coordinates for Na(Y1.5Na0.5)F6: Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ
samples.
Labels
Samples
Excitation nm
CIE (x, y)
1
2
3
4
5
6
7
8
0.02Dy3þ
348
348
348
368
368
368
368
368
368
356
356
356
356
356
384
384
384
384
384
384
384
384
356
356
356
356
356
356
360
360
360
360
360
(0.352,0.401)
(0.352,0.432)
(0.354,0.458)
(0.268,0.337)
(0.325,0.477)
(0.380,0.455)
(0.413,0.432)
(0.477,0.395)
(0.483,0.384)
(0.171,0.077)
(0.199,0.252)
(0.222,0.312)
(0.276,0.324)
(0.374,0.351)
(0.346,0.367)
(0.398,0.377)
(0.431,0.384)
(0.453,0.386)
(0.471,0.387)
(0.478,0.382)
(0.487,0.379)
(0.498,0.380)
(0.204,0.122)
(0.236,0.187)
(0.245,0.217)
(0.275,0.270)
(0.279,0.280)
(0.290,0.299)
(0.298,0.367)
(0.314,0.360)
(0.319,0.342)
(0.328,0.334)
(0.342,0.342)
0.02 Dy3þ, 0.01 Tb3þ
0.02 Dy3þ, 0.03 Tb3þ
0.03 Tb3þ
0.03 Tb3þ, 0.01Eu3þ
0.03 Tb3þ, 0.02 Eu3þ
0.03 Tb3þ, 0.03 Eu3þ
0.03 Tb3þ, 0.05 Eu3þ
0.03 Tb3þ,0.06Eu3þ
0.03 Tm3þ
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
0.03 Tm3þ, 0.005 Ho3þ
0.03 Tm3þ, 0.01 Ho3þ
0.03 Tm3þ, 0.015 Ho3þ
0.03 Tm3þ, 0.02 Ho3þ
0.03 Dy3þ
0.03 Dy3þ, 0.01Eu3þ
0.03 Dy3þ, 0.02Eu3þ
0.03 Dy3þ, 0.03Eu3þ
0.03 Dy3þ, 0.04Eu3þ
0.03 Dy3þ, 0.05Eu3þ
0.03Dy3þ,0.06Eu3þ
0.03Dy3þ, 0.07Eu3þ
0.01 Tm3þ
0.01 Tm3þ,0.005Dy3þ
0.01 Tm3þ,0.02Dy3þ
0.01 Tm3þ,0.03Dy3þ
0.01 Tm3þ,0.04Dy3þ
0.01 Tm3þ,0.05Dy3þ
0.05Dy3þ, 0.02 Tb3þ, 0.01Eu3þ
0.05Dy3þ, 0.02 Tb3þ, 0.02Eu3þ
0.05Dy3þ, 0.02 Tb3þ, 0.03Eu3þ
0.05Dy3þ, 0.02 Tb3þ, 0.04Eu3þ
0.05Dy3þ, 0.02 Tb3þ, 0.05Eu3þ
Fig. 14. Emission spectra of Na(Y1.5Na0.5)F6：3%Tb3þ, 2%Eu3þ
temperature range between 298 and 358 K (a), and that between 368 and 448 K (b),
and that between 458 and 498 K (c).
(
lex ¼ 368 nm)in the
9

H. Guan and Y. Li
Journal of Alloys and Compounds xxx (xxxx) xxx
and ultimately to blue green by adjusting the doped concentration
of Ho3þ ions. In Na(Y1.5Na0.5)F6: Dy3þ, Eu3þ excited at 384 nm, the
trend of their color tones changes from light yellow to yellow and
ultimately to orange red by adjusting the doping concentration of
Eu3þ, which are presented in Fig. 13 (B points 15e22). In addition, it
can be see that the corresponding color tone of the Na(Y1.5Na0.5)F6:
Tm3þ, Dy3þphosphors shifted from blue through light blue and
ultimately to cool white under the excitation of 356 nm UV light, as
show in Fig. 13(B, 23-28). More importantly, it is seen that the
desirable warm white emission can be realized by the triple-doping
of Dy3þ, Tb3þ, Eu3þ in Na(Y1.5Na0.5)F6. The results show that the
emission color of Na(Y1.5Na0.5)F6: RE3þ can be turned by adjusting
the amount of rare earth ions and changing the kind of rare earth
ions.
architectures of inorganic materials. Hereby, Na(Y1.5Na0.5)F6:
RE3þ(Dy3þ,Tb3þ,Eu3þ,Tm3þ,Ho3þ) was first successfully prepared
by glycine acid assisted hydrothermal method.The size and shape of
the products could be tuned just by adjusting the pH values of the
initial reaction solutions or by adjusting the RE3þ/NaF ratio or RE3þ
/
NaBF4 ratio. The morphologies for the products include spindle-like
microstructures, six prismatic, irregular microrods, micron hexag-
onal prisms and nano-spheres, micron elliptical disc, flower-like
microstructures, spindle-like structures and irregular bulk.
Furthermore, we systematically investigate the luminescence
properties of different lanthanide ions (Dy3þ, Tb3þ, Eu3þ, Tm3þ
,
Ho3þ) in Na(Y1.5Na0.5)F6 host. Importantly, the thermal stability of
the phosphors of the prepared sample is excellent.
As it is known, the thermal quenching property is a very
important parameter of luminescence materials. Therefore, under
368 nm excitation, the temperature dependence of the lumines-
cence spectra of Na(Y1.5Na0.5)F6：3%Tb3þ, 2%Eu3þ is measured, as
shown in Fig. 14. Note that, with increasing temperature, the in-
tegrated photoluminescence intensities only slightly changed while
the peak positions almost keep still, as shown Fig. 14a, b, c. With
increasing temperatures (298 Ke358 K), the emission intensity of
Na(Y1.5Na0.5)F6：3%Tb3þ, 2%Eu3þ is barely changed. When the
Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgements
This present work was financially supported by the Science and
Technology Fund project of Changchun Institute of Technology
(Grant No.320200018).
temperature reaches 368 K, the emission intensity of Na(Y1.5Na0.5
F6：3%Tb3þ, 2%Eu3þ decreases slightly. As the temperature in-
creases to 448 K, the emission intensity of Na(Y1.5Na0.5)F6: 3%Tb3þ
2%Eu3þ hardly changes during this interval. However, when the
)
,
References
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stant. The above results indicate that the excellent thermal stability
of Na(Y1.5Na0.5)F6：3%Tb3þ, 2%Eu3þ phosphors.
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