Size and morphology-controlled synthesis of vernier yttrium oxyfluoride towards enhanced photoluminescence and white light emission

Article abstract of DOI:10.1039/c8nj01962b

In this study, a class of vernier yttrium oxyfluoride (Y₅O₄F₇ denoted as V-YOF) with a variety of shapes and sizes was formed by adjusting the crystal growth environment; after calcination, the samples can maintain the morphology of the precursor; this may be attributed to the topotactic chemical transformation. A comparison of the fluorescence results shows that the hexagonally shaped microcrystal strips can effectively improve the light-emitting characteristics; further, to explore the growth mechanism of precursors, time-dependent experiments and three-dimensional growth simulations have been carried out. They suggest that the formation of hexagonal strips may be due to the unique way that the crystals grow from the interior space to the outer wall. Moreover, Tm³⁺/Dy³⁺-codoped V-YOF phosphors exhibit excellent white light emission (CIE: x = 0.338, y = 0.313 close to that of standard white light (0.33, 0.33)) due to energy transfer. These results confirm that the V-YOF phosphors may have potential applications in the field of luminescent materials.

Full text of DOI:10.1039/c8nj01962b

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
Size, morphology controlled synthesis of vernier yttrium
oxyfluoride towards enhanced photoluminescence and white light
emission
Received 00th January 20xx,
Accepted 00th January 20xx
Jianchao Dong, Hailong Xiong, Xiaoxue Wang, Lina Song, Yali Liu, Junfeng Yang, Hongyue
Wu, Chunming Yang, Shucai Gan*
DOI: 10.1039/x0xx00000x
www.rsc.org/
In this paper, one class of vernier yttrium oxyfluoride (Y5O4F7 denoted as VꢀYOF) with
variety of shapes and sizes was described, which formed by adjusting the crystal growth
environment. The samples after calcining can maintain the morphology of the precursor may
attribute to the topotactic chemical transformation. The comparison of fluorescence results
shows that the shape of hexagonal strips microcrystals can effectively improve the lightꢀ
emitting characteristics. And in order to explore the growth mechanism of precursors, timeꢀ
dependent experiments and threeꢀdimensional growth simulations suggest that the formation
of hexagonal strips may be due to the unique way that the crystals grow from the interior space
to the outer wall. Besides, Tm3+/Dy3+ codoped VꢀYOF phosphors exhibit excellent white light
emission (CIE:x = 0.338, y = 0.313 close to the standard white light (0.33,0.33) ) due to the
energy transfer. These results confirmed that the VꢀYOF phosphors may have potential
applications
in
field
of
luminescent
materials.
1. Introduction
and various doping sites. Oxygen and fluorine anions in
the structure suffer a stoichiometric deviation resulting in
changes to the anion substructure following the vernier
effect proposed by Hyde et al. The assorted array of O2ꢀ
and Fꢀ ions in the a × nb × c unit cell offers highly
disordered host lattice, which provides several multiple
low symmetry crystallographic sites (C1, C2 and Cs)
suitable for f–f transitions of the RE3+ dopants and thus
gives rise to intense luminescence6ꢀ8. Hitherto, vernier
oxyfluorides9 have been successfully synthesized by T.
Wen et al.10 and W. Luo et al11.
In recent years, Lanthanide doped nano
/
microluminescent materials have been growing extensive
investigation due to their wide range of applications. In
particular, the research in the area of rare earth
oxyfluorides (REOF) is thriving not only through the rich
structural varieties observed in the materials but also
through their widely varying luminescence properties that
promise potential applications. Due to their low phonon
energy, high ionicity, high chemical and thermal stability1,
lanthanide oxyfluorides (REOFs) have aroused extensive
interest for applications in biosensing2, optical
According to the literature12, the shape and size of rare
nanodevices3, fieldꢀemissionꢀdriven phosphors4, Xꢀray earth doped luminescent materials have significant
detectors, and efficient solar cells5. Among the rare earth influnce to their property13, such as drug carrying14ꢀ16, gene
oxyfluorides, the more accurate analysis of the vernier delivering17,18
,
cell labeling19ꢀ21
,
and multicolor
phase oxyfluorides have shown that REnOnꢀ1Fn+2 (RE= Y, fluorescence22,23. Therefore, the tremendous efforts have
Lu, Yb, 5 ≤ n ≤ 7) have complex structural characteristics been dedicated to the morphology and size controllable
synthesis of nanoꢀ/micromaterials. Expressly, vernier
oxyfluorides that obtained from calcining precursors
College of Chemistry, Jilin University, Changchun
130026, P.R. China
hardly maintained the morphology of the precursor
because of its diverse structural features. It has become a
major limiting factor of improving the fluorophores'
fluorescence performance and retaining a challenge to
control the size, shape of vernier oxyfluorides phosphors.
*Corresponding author: Shucai Gan.
On the basis of previous work24,25. Herein, a series of
vernier yttrium oxyfluoride with controlled size and
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morphology was synthesized by facile hydrothermal were prepared by changing the fluorine source and pH
approach and topotactic transformation without any under the same conditions.
organic ligands. The comparison of fluorescence 2.3 Characterization
characteristics indicates that the VꢀYOF microcrystal with
The samples were examined by powder Xꢀray
the shape of hexagonal strips can be promising as a diffraction (XRD) measurements performed on a Rigaku
potential candidate for the application in lightꢀemitting D/maxꢀII B Xꢀray diffractometer at a scanning rate of 10°
field. In addition, the energy transfer mechanism from minꢀ1 in the 2θ range from 10° to 70°, with graphiteꢀ
Fig. 1 XRD patterns of asꢀprepared Y(OH)1.57F1.43 (a),
Y5O4F7 (b). The standard data for VꢀYOF (PDF card no.
80ꢀ1124) and Y(OH)1.57F1.43 (PDF card no. 80ꢀ2008) is
presented at the bottom for comparison.
Tm3+ to Dy3+ has been researched in detail.
2. Experimental
monochromatic Cu Kα radiation (λ = 0.15406 nm). The
morphology, dimension, and composition of products were
examined by scanning electron microscope (SEM, Sꢀ4800,
Hitachi) equipped with an energyꢀdispersive Xꢀray
2.1 Chemicals
spectrometer
(EDX,
JEOL
JXAꢀ840).
The
photoluminescence excitation (PLE), emission (PL)
spectrum and the luminescence decay curves were
recorded with a Jobin Yvon FluoroMaxꢀ4 equipped with a
150 W xenon lamp as the excitation source. Lowꢀ/highꢀ
resolution transmission electron microscopy (TEM) was
performed using a FEI Tecnai G2SꢀTwin instrument with a
fieldꢀemission gun operating at 200 kV. All measurements
were performed at room temperature.
RECl3 was prepared by dissolving the corresponding
RE2O3 and Tb4O7 (99.99%) in dilute HCl solution at
elevated temperature with agitation. Other chemicals were
purchased from Beijing chemical Co. All chemicals were
of analytical grade and were used directly without further
purification.
2.2 synthetic procedures for VꢀYOF microcrystal
3. Results and discussion
3.1 Phase identification and morphology.
YCl3 aqueous solution (0.11 M, 10 mL) was completely
mixed with NaF (0.0693 g, 1.65 mmol) under vigorous
stirring at room temperature. Thereafter, 20 mL deionized
water was introduced and the pH value of the resultant
mixing solution was adjusted to 10 by adding NaOH
aqueous solution. After stirring for 20min, it was
transferred to a 50 mL autoclave and maintained at 100 oC
for 5 h, then cooled down naturally to room temperature.
The resulting white precipitates were collected by
centrifugation, washed three times with ethanol and
Xꢀray diffraction analysis (XRD) of the precursor is
wellꢀmatched with that of Y(OH)1.57F1.43 hexagonal phase
o
(PDF No. 80ꢀ2008) (Fig. 1a). After calcination at 550 C
for 2h, all the peaks are consistent with the standard PDF
card No. 80ꢀ1124 of VꢀYOF powder, indicating that the
obtained samples are in single phase (Fig. 1b). The
representative SEM images show that Y(OH)1.57F1.43
exhibited rugbyꢀlike microparticles (Fig. 2a,b) that
synthesized at pH = 8. When the pH value of the solution
was adjusted to 10, the precursor with the shape of
hexagonal strips was formed (Fig. 2c). The EDS spectrum
of Y(OH)1.57F1.43 (Fig. 2d) confirms the presence of the Y,
O, and F elements, which further suggests the purity of the
precursor.
o
deionized water, finally dried at 60 C in air for 12 h. The
VꢀYOF sample was obtained through calcining the
Y(OH)xF3ꢀx precursor at 550 oC for 2 h. VꢀYOF:Ln3+(Ln =
Eu, Tb, Dy, Tm) microcrystals were prepared by the same
process, except that a certain amount of LnCl3 instead of
the same amount of YCl3 was introduced. Other samples
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Fig. 2 SEM picture of the asꢀprepared Y(OH)1.57F1.43
at pH = 8 (a),(b), pH = 10 (c). EDS spectra of
precursor (d).
Fig. 4 Schematic diagram of the orthorhombic Vernier
phase structure of VꢀYOF and three kinds of
coordination for Y3+.(a) The crystal structures of
Y(OH)xF3ꢀx and VꢀYOF viewed along aꢀaxis(b).
Fig. 3 SEM images of the samples prepared at pH = 8 (a) and pH = 10 (b) with NaF. The SEM images of
the samples prepared at pH = 8 with different F− sources, NH4F (c), KF (d).
The synthesis of the crystals is dominated by dimensions marked in the illustrations, corresponding to
experimental variables that affect nucleation and growth the dimensions of the samples in the insert map.
rates. Among them, environment played an important role
in controlling crystal growth, which was substantiated by
The crystal structure of [YnOnꢀ1Fn+2 (n=5)] is shown in
adjusting pH value to tune the dimensions and morphology Fig. 4a, this orthorhombic structure gives rise to three
characteristics of the samples. For example (Fig. S1), in different Y positions for different coordination numbers
the range of pH value from 8 to 10, the target precursor and coordination atoms: Y1, Y2 in C1 symmetric sites, Y3
can be obtained. At higher alkaline environment of in CS sites, and thus different coordination environments
reaction (pH = 11), the diffraction peak of precursor for possible Ln3+ cation substitution. Fig. 4b shows the
disappeared completely. Accordingly, we obtained rugbyꢀ Y(OH)xF3ꢀx crystal structure expressed in the form of a
shaped microcrystals with an appropriate size of 4ꢀ6 ꢁm in polyhedron, Y coordinates with nine oxygen atoms to form
length at pH = 8, 9. (Fig. 3a) On further increasing the pH Y(O/F)9 polyhedron. And the Y(O/F)9 polyhedron is
value to 10, the products are mainly composed of linked to other polyhedron by edges along bꢀ and cꢀaxis
hexagonal strips microcrystals, and about 4–5 ꢁm in length forming a 2D crystal network of polyhedron, which is
(Fig. 3b). In addition, the detailed effects of the different similar to that of VꢀYOF polyhedral structure. In the
F− sources on the morphologies of the final products had calcination process, Y(O/F)9 polyhedron is distorted into
been researched. When NH4F and KF as F− sources at pH three different polyhedra. Based on these similarities, the
= 8 are shown in Fig. 3c, d, the morphologies of the product inherits almost completely the morphology of the
obtained VꢀYOF are quite different. The corresponding precursor 26ꢀ28
shape diagram has been represented vividly, and the
.
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Fig. 5 Temporal evolution of the Y(OH)xF3ꢀx microcrystals in the hydrothermal synthesis, 30min (a), 1h (b),
2h (c), 3h (d), 5h (e).
keeping the other reaction parameters unchanged (NaF as
F− source, pH = 10). In the first stage for reaction 30 min
(Fig. 5a), a fast nucleation process occurred and a large
amount of lumpy gel was formed. On prolonging the
reaction time for 1 h (Fig .5b), the surface of the block
began to appear microrods. When the reaction time reaches
2h and 3h, the massive gel disappeared and the microrods
growed further. The threeꢀdimensional schematic clearly
describes this process of growth. Obviously, reaction time
is between 2h and 5h, the microrods grow closely from the
interior space to the outer wall by a kinetically controlled
crystal growth process. Based on this growth pattern, the
outer edges and corners of the crystal start to be distinct,
and at the same time, tiny holes have formed inside (Fig.
5c,d). Finally, microcrystal formed completely for reaction
5h (Fig. 5e). The hole pattern of the sample is represented
by a threeꢀdimensional crossꢀsectional view, it can be seen
that the formation of the channel is not completely hollow.
Fig. 6 show the TEM images of the precursor at 2h (a), 3h
Fig. 6 TEM images of the precursor at 2h(a, b), 3h
(c) of the reaction and XRD patterns of the
corresponding timeꢀdependent experiments (d).
In order to understand the growth mechanism of the Vꢀ (c) and XRD patterns of the corresponding timeꢀdependent
YOF microꢀcrystal with the shape of hexagonal strips, experiments (d). It can be clearly seen from the XRD
timeꢀdependent experiments have been carried out by pattern that no crystal structure has been formed when
reacting for 30 minutes.When the reaction was carried out
for 1 h, the crystal phase began to form gradually, and
diffraction peaks began to appear. As the time went by, the
crystal growth became complete, and the intensity of the
diffraction peaks increased. In addition, the corresponding
electron micrographs further proved the formation of rodꢀ
like structures.
The elemental mapping of precursors and VꢀYOF
samples for Y, F, and O shown in Fig. 7. Additional
scanning electron micrographs and corresponding
elemental diagrams clearly show the tiny holes of
precursors and products, and from Figure 7b can be seen
that in the product’s growth process, the outer edges and
corners are clearly like a combination of six rods with a
sixꢀpage petal shape on the side. The TEM and HRTEM
images (Fig .8) of VꢀYOF provide further insight into the
structure and composition of the obtained products, The
internal hole can be seen through distinct bright/dark
contrast from TEM image of a single crystal (Fig. 8b).
Fig. 7 SEM image of precursors (a), elemental
mapping of precursor (right), SEM image of
precursors (b), The corresponding elemental
mapping (right).
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Based on the HRTEM and SAED pattern analysis image nm (4F9/2
ARTICLE
→
6H13/2). Meanwhile, we investigated the
(Fig. 8c), distinct 2D lattice fringes of VꢀYOF (200) planes fluorescence of different morphological samples
can be seen clearly, suggesting the high crystalline.
Fig.
9
Contrast of PL spectra of Vꢀ
YOF:0.05Ln3+(Ln=Eu, Tb, Tm, Dy) with different
morphologies, samples prepared at pH=8 with NaF (a),
pH=8 with NH4F (b), pH=8 with KF (c), pH=10 with
NaF (d).
Fig. 8 TEM images of VꢀYOF(a,b) and HRTEM
and SAED image (c).
3.2 Photoluminescence Properties.
3.2.1 Luminescence properties of VꢀYOF:Ln3+ (Ln = Tb,
Eu, Tm).
respectively. Fig. 9 exhibits the fluorescent contrast of Vꢀ
YOF:(Ln3+ = Tb, Eu, Tm, Dy). It is obvious that all the
samples share an identical spectral pattern with distinct
differences in the intensity. Among them, the fluorescence
intensity of VꢀYOF (synthesized at pH = 10, NaF as F−
sources) is much higher than the fluorescence intensity of
the synthesized product under other conditions. The results
show that VꢀYOF microcrystals with the shape of
hexagonal strips as a fluorescence host can effectively
enhance the luminescence effect.
Fig. S3a exhibits the excitation and emission spectra of
the asꢀprepared VꢀYOF:Eu3+. Under the monitoring of 614
nm wavelength, the excitation spectrum sharp peaks at
320, 362, and 393 nm which are ascribed to the 7F0 → 5H3,
7F0
→ →
5D4, and 7F0 5L6 transitions of Eu3+. Upon
excitation with 242 nm irradiation, the VꢀYOF:Eu3+ gives
peaks at 537 nm (5D1 → 7F1), 580 nm (5D0 → 7F0), 595 nm
7
7
(5D0 → F1), 614, 625 nm (5D0 → F2), and 652 nm (5D0
→ F3)29,30. Fig. S3b presents the PLE and PL spectra of
7
VꢀYOF:0.05Tb3+. The PL spectrum excited at 228 nm
shows certain peaks at 488 nm, 544 nm, 586 nm and 623
3.2.2 Polychromatic luminescence and energy transfer
(ET) mechanism.
We synthesize Tm3+/Dy3+ coꢀdoped VꢀYOF samples in
the same way so as to obtain multicolor tunable
luminescence and white lightꢀemitting. Fig. 10 illustrates
the dependence of PL spectra for VꢀYOF:0.01Tm3+, xDy3+
(x = 0ꢀ0.045) phosphors under the 359 nm excitation.
According to Figure S4 and previous studies32, it can be
determined that there is energy transfer between Tm and
Dy, therefore, the PL spectra of Tm3+, Dy3+ coꢀdoped have
both characteristic emissions of Tm3+ and Dy3+. And it can
be seen from the fig.S5 that as the concentration of Dy3+
increases, the relative luminescence intensity of Dy3+ and
Tm3+ changes due to the energy transfer.
nm, corresponded to 5D4
→
7FJ (J = 6, 5, 4, 3),
respectively31. As for VꢀYOF:Tm3+ (Fig. S3c), monitored
at 456 nm, the PLE spectrum shows certain peaks at 260
nm (3P2 → H6)and 359 nm (3H6 → D2). Excitation into
3
1
the strongest H6 → D2 transition of Tm3+ yields the
3
1
corresponding emission spectrum, in which the main
1
3
emission peak at 456 nm is assigned to the D2 → F4
electronic dipole transition. In Fig S3d, monitored at 456
nm, the PLE and PL spectrum show the characteristic
absorption peaks of Dy3+: 351 nm (6H15/2 → 6P7/2), 365 nm
(6H15/2
→
6P5/2), 386 nm (6H15/2
→
4F7/2+4I13/2) and
6
characteristic emission peak: 487 nm (4F9/2 → H15/2), 575
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Fig. 10 PL spectra for VꢀYOF:0.01Tm3+, xDy3+ (X=
0ꢀ0.045) samples.
xDy3+ fit the single exponential rule by the following
equation33:
Where I and I0 are the luminescence intensities at times t
and 0, respectively, τ is the luminescence life time. On the
basis of the above equation and decay curves, the lifetimes
of Tm3+ in VꢀYOF:0.05Tm3+, xDy3+ phosphors are 9.04,
6.75, 5.87, 5.46, 3.98, 2.75 and 1.90 ms for x = 0, 0.005,
0.010, 0.015, 0.025,0.035, 0.045. The energy transfer
efficiency (ηT) from Tb3+ to Eu3+ can be calculated by the
formula as follows34:
where τs and τs0 are the relative lifetimes of Tm3+ with and
without the presence of the Dy3+ ions, and ηT is the
calculation of energy transfer efficiency. The ET
efficiency for VꢀYOF:0.01Tm3+,xDy3+ was about 25.3%,
34.9%, 39.6%, 55.9%, 69.5%,and 78.9%, respectively.
From Figure S5, as the concentration of Dy3+ increases, the
energy transfer efficiency increases, and the fluorescence
lifetime of Tm3+ decreases, and these results well
demonstrate the existence of energy transfer.
Fig. 11 Decay curves for the luminescence of Tm3+
ions in VꢀYOF.
By investigating the decay curves of Tm3+, the ET from
Tm3+ to Dy3+ can be validated. Fluorescence decay curves
obtained by the excitation at 359 nm and monitored at 456
nm and the results are shown in Fig. 11. All the
luminescent decay times of Tm3+ in VꢀYOF:0.05Tm3+,
To explore the mechanism of energy transfer from Tm3+
to Dy3+ ions, the following model was employed35,36
:
)
− t
τ
(1)
I = I 0 + Ae
τ
s
(2)
η
= 1 −
T
τ
s
0
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The energy transfer between these two ions is thought to
be a resonant energy transfer process because the spectral
overlap between the emission of the donor (Tm3+) and the
n
τ
s 0
3
∝ C Tm + Dy
(3)
τ
s
Fig. 14 The CIE chromaticity diagram of the Vꢀ
YOF:0.01Tm3+, xDy3+.
absorption of the acceptor (Dy3+) is present. Fig. 13
illustrates the ET model, Tm3+ ions absorb the energy,
3
1
energy transitions from the H6 level to the D2 level,
4
subsequently, a part of energy shifts to the I11/2 state of
Dy3+. Then the energy of 4I11/2 transfers to the 4F9/2 energy
level by the crossrelaxation process, and finally transfers to
the 6H15/2 and 6H13/2 level of Dy3+ by radiative transition.
Fig. 14 and Tab. 1 show the Commission Internationale
de L’Eclairage (CIE) chromaticity coordinates of Vꢀ
YOF:0.01Tm3+, xDy3+. The luminescent color can be
tuned from blue to white by changing the doping
concentration of Dy3+. Tab. 1 shows the calculation of the
CIE coordinates and correlated color temperature that can
6/3
Fig. 12 Dependence of τs0/τs of Tm3+ on CTm+Dy
×
104, CTm+Dy
× 105, CTm+Dy
× 106 in the
8/3
10/3
phosphors.
Where τs0 is the intrinsic lifetime of Tm3+, τs is the lifetime
of Tm3+ in the presence of the Dy3+, C is the dopant
concentration of Tm3+ and Dy3+, and n = 6 , 8 ,10
correspond to dipoleꢀdipole, dipoleꢀquadrupole, and
quadrupoleꢀquadrupole interactions, respectively. Fig. 12
shows that the best linear relationship is obtained when
n=8, which demonstrates that the energy transfer
mechanism is a nonradiative dipoleꢀquadrupole interaction
type.
be calculated by the following formula37,38
:
T = −437n3 + 3601n2 − 6861n + 5514.31
Where n = (x ꢀ 0.3320)/(y ꢀ 0.1858). Furthermore, the CIE
chromaticity diagrams of VꢀYOF:0.05Ln3+(Ln=Dy, Tb,
Tm, Eu) synthesized under different conditions(Fig. S6
and Table. S1) indicate that under the same doping
concentration, the phosphors with different morphologies
will have different coloration effects (Corresponding to the
PL spectrum). For example, The morphology and size of
the sample have a greater effect on the fluorescence of Tm
ions and Dy ions, the fluorescence of Vꢀ
YOF:0.05Tm3+(KF as the Fꢀ source pH=8) is close to the
standard blue light (0.14, 0.08). These results indicate that
proper size and morphology play an integral role in the
fluorescence effect.
Table. 1 CIE chromaticity coordinates (x, y) for Vꢀ
YOF:0.01Tm3+, xDy3+ samples.
Fig. 13 Energy level scheme representing the energy
transfer and energy transfer mechanism in the Tm3+,
Dy3+ꢀcodoped VꢀYOF phosphors.
Sample
Sample compositions
CIE(x,y)
CCT
(K)
no.
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a
b
VꢀYOF:0.01Tm3+
(0.159,0.056)
(0.236,0.160) 85745
2353
9 T. Grzyb, R. J. Wiglusz, V. Nagirnyi, A. Kotlov, and S.
Lis, Dalton Trans., 2014, 43, 6925ꢀ34.
Vꢀ
YOF:0.01Tm3+,0.005Dy3+
10 T. Wen, W.J. Luo, Y.G. Wang, M. Zhang, Y.Z. Guo, J.
Yuan, J. Ju, Y. Wang, F. Liao and B.F. Yang, J. Mater.
Chem. C, 2013, 1, 1995ꢀ2001.
c
d
e
Vꢀ
(0.279,0.219)
(0.287,0.261) 10796
(0.338,0.313) 5161
31410
YOF:0.01Tm3+,0.015Dy3+
Vꢀ
YOF:0.01Tm3+,0.035Dy3+
Vꢀ
YOF:0.01Tm3+,0.045Dy3+
11 W.J. Luo, Y.G. Wang, Y.P. Chen, T. Wen, M. Liu,
Y.X. Wang, F.H. Liao, and J.H. Lin, J. Mater. Chem. C,
2013, 1, 5711ꢀ5717.
4. Conclusions
12 T. Wen, Y.N. Zhou, Y.Z. Guo, C.M. Zhao, B.C. Yang,
and Y.G. Wang, J. Mater. Chem. C, 2016, 4, 684ꢀ90.
In summary, we reported on the fabrication of a class of
VꢀYOF phosphors for enhancement of photoluminescence
by controlling the size, morphology of samples. Because
of the topological transformation, the morphology before
and after calcination can be well preserved. The
fluorescence contrast of VꢀYOF:Ln3+ with differernt
shapes shown that microcrystals with the shape of
hexagonal strips may be used as excellent fluorescent
material. And by coꢀdoping Tm3+ and Dy3+ into VꢀYOF
13 X.L. Liu, W.H. Hou, X.Y. Yang and J.Y. Liang,
CrystEngComm, 2014, 16, 1268.
14 Y. Zhang, D.L. Geng, X.J. Kang, M.M. Shang, Y. Wu,
X. Li, H. Lian, Z. Cheng, and J. Lin, Inorg. Chem., 2013,
52, 12986ꢀ94.
host, white light emission can be obtained due to the 15 R.C. Lv, S.L. Gai, Y.L. Dai, F. He, N. Niu, and P.P.
energy transfer from Tm3+ to Dy3+ (a dipoleꢀquadrupole Yang, Inorg. Chem., (2014), 53, 998ꢀ1008.
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16 Xu, Z. P.; Zeng, Q. H.; Lu, G. Q.; Yu, A. B, Chem. Eng.
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mechanism and crystal growth process may provide new
insight into the design of highꢀperformance optical
materials.
17 Lanza, G. M.; Yu, X.; Winter, P. M.; Abendschein, D.
R.; Karukstis, K. K.; Scott, M. J.; Chinen, L. K.; Fuhrhop,
R. W.; Scherrer, D. E.; Wickline, S. A. Circulation, 2002,
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Acknowledgements
This present work was financially supported by China
GeologicalSurvey (Grant No. 12120113088300); and the
Key Technology and Equipment of Efficient Utilization of
Oil Shale Resources, No. OSRꢀ5.
18 Jiao, Y. F. Guo. J, Shen, S.; Chang, B. S.; Zhang, Y. H.;
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