Color-tunable luminescence of Y4Si2N 2O7:Ce3+, Tb3+, Dy3+ Phosphors prepared by the soft-chemical ammonolysis method

Article abstract of DOI:10.1002/ejic.201400001

Ce³⁺-, Tb³⁺-, and Dy³⁺-activated Y ₄Si₂N₂O₇ phosphors have been prepared by the Pechini-type sol-gel method followed by ammonolysis of the precursors. The phase purity, morphology, crystallization condition, chemical composition, and thermal stability of the products have been studied carefully by X-ray diffraction (XRD), energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), fourier-transform infrared (FTIR), and thermogravimetry analysis (TGA) techniques. The photoluminescence (PL) and cathodoluminescence (CL) properties of Ce³⁺-, Tb³⁺-, and Dy³⁺-doped Y ₄Si₂N₂O₇ phosphors were also investigated. The electronic structure of Y₄Si₂N ₂O₇ has been investigated by density-functional theory methods. The calculations revealed that the nitrogen atom contributes more excited electrons than the O atom. The band gap has been calculated through the reflection spectrum of the Y₄Si₂N₂O₇ host. For Ce³⁺/Tb³⁺/Dy³⁺ singly doped Y ₄Si₂N₂O₇ products, the phosphors give the typical emissions of the activators. The energy transfers from Ce ³⁺ to Tb³⁺ and Dy³⁺ ions have been found and demonstrated through the PL spectra and luminescence decay times. The emission color of Y₄Si₂N₂O₇:Ce³⁺, Tb³⁺ and Y₄Si₂N₂O ₇:Ce³⁺, Dy³⁺ samples can be tuned by energy transfer processes. Additionally, the temperature-dependent PL properties and the degradation property of CL under continuous electron bombardment of the as-synthesized phosphors prove that the Y₄Si₂N ₂O₇ host has good stability. Therefore, the Y ₄Si₂N₂O₇:Ce³⁺, Tb ³⁺, Dy³⁺ phosphors could serve as a promising candidate for UV W-LEDs and FEDs. Copyright

Full text of DOI:10.1002/ejic.201400001

FULL PAPER
DOI:10.1002/ejic.201400001
Color-Tunable Luminescence of Y4Si2N2O7:Ce3+, Tb3+,
Dy3+ Phosphors Prepared by the Soft-Chemical
Ammonolysis Method
Dongling Geng,[a,b] Kai Li,[a] Hongzhou Lian,[a]
Mengmeng Shang,[a,b] Yang Zhang,[a,b] Zhijian Wu,[a] and
Jun Lin*[a]
Keywords: Energy transfer / Luminescence / Phosphors / Yttrium / Sol-gel processes / Oxonitridosilicates
Ce3+-, Tb3+-, and Dy3+-activated Y4Si2N2O7 phosphors have
been prepared by the Pechini-type sol–gel method followed
by ammonolysis of the precursors. The phase purity, mor-
phology, crystallization condition, chemical composition, and
thermal stability of the products have been studied carefully
by X-ray diffraction (XRD), energy-dispersive X-ray (EDX),
scanning electron microscopy (SEM), high-resolution trans-
atom. The band gap has been calculated through the reflec-
tion spectrum of the Y4Si2N2O7 host. For Ce3+/Tb3+/Dy3+ sin-
gly doped Y4Si2N2O7 products, the phosphors give the typi-
cal emissions of the activators. The energy transfers from
Ce3+ to Tb3+ and Dy3+ ions have been found and demon-
strated through the PL spectra and luminescence decay
times. The emission color of Y4Si2N2O7:Ce3+, Tb3+ and
mission electron microscopy (HRTEM), fourier-transform in- Y4Si2N2O7:Ce3+, Dy3+ samples can be tuned by energy trans-
frared (FTIR), and thermogravimetry analysis (TGA) tech-
niques. The photoluminescence (PL) and cathodolumin-
escence (CL) properties of Ce3+-, Tb3+-, and Dy3+-doped
Y4Si2N2O7 phosphors were also investigated. The electronic
structure of Y4Si2N2O7 has been investigated by density-
functional theory methods. The calculations revealed that the
nitrogen atom contributes more excited electrons than the O
fer processes. Additionally, the temperature-dependent PL
properties and the degradation property of CL under con-
tinuous electron bombardment of the as-synthesized phos-
phors prove that the Y4Si2N2O7 host has good stability.
Therefore, the Y4Si2N2O7:Ce3+, Tb3+, Dy3+ phosphors could
serve as a promising candidate for UV W-LEDs and FEDs.
tices and the high covalency of the crystal structures.[3] In
the structure of oxonitridosilicates, the nitrogen atom of the
SiN4 tetrahedra can be partially replaced by oxygen to form
Si[O/N]4 tetrahedra, and the Si[O/N]4 units are stacked to-
gether by sharing their corners or edges to form a con-
densed framework, resulting in the excellent thermal and
chemical stability of oxonitridosilicate.[4] Oxonitridosilicates
substituted by rare earths have been widely used as phos-
phors in LED lamps, for instance green M3Si6O12N2:Eu2+
(M = Sr, Ba), green β-sialon, yellow α-sialon, red M2Si5N8
(M = Ca, Sr and Ba), and CaAlSiN3 phosphors.[5] As we
know, nitride and oxynitride phosphors are usually synthe-
sized through solid-state reactions under vacuum, N2/H2
mixtures, or N2 at high temperature (typically 1400–
1800 °C), and high pressure.[6] The nitride raw materials
and glove boxes are needed in the preparation of nitrogen
containing phosphors.[7] So, this widely employed conven-
tional solid-state process often suffers from the high cost,
high-energy consumption, and long reaction time. There-
fore, developing an economical mass production and envi-
ronmentally friendly method is highly desirable. Recently,
Introduction
In recent years, nitride and oxynitride phosphors have
been extensively developed as important luminescent mate-
rials with good color tunability, low toxicity, and high
quantum efficiency.[1] Among them, the oxonitridosilicates
have demonstrated remarkable advantages as host materials
for phosphors used in phosphor converted light-emitting di-
odes (pc-LEDs) because of their outstanding thermal and
chemical stability, excellent luminescence properties, and
structural diversity.[2] Compared with the silicate phos-
phors, oxonitridosilicate phosphors usually have longer
wavelength excitation (emission) bands and excellent sta-
bility towards oxidation, hydrolysis, and high temperature.
This is because of the strong crystal fields of the host lat-
[a] State Key Laboratory of Rare Earth Resource Utilization,
Changchun Institute of Applied Chemistry, Chinese Academy
of Sciences,
Changchun 130022, P. R. China
E-mail: jlin@ciac.ac.cn
http://sourcedb.cas.cn/sourcedb_ciac_cas/en/ywrck/ywyjy/
200907/t20090709_2051188.html
[b] University of Chinese Academy of Sciences,
Beijing 100049, P. R. China
Thomas et al. reported new luminescent oxynitrides La10–x
-
Srx(Si/Ge)6O27–x/2–3y/2Ny:Eu, Ce using the ammonolysis of
doped apatite oxysilicate precursors, which were obtained
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201400001.
Eur. J. Inorg. Chem. 2014, 1955–1964
1955
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
by the solid-state method.[8] Yet, repeating sintering at high it is possible to obtain the adjustable emissions of activators
temperature has little effect on saving the preparation time in the Y4Si2N2O7 host.
and energy. Hence, a more convenient and energy-saving
method is very necessary. In addition, among all the re-
ported nitride and oxynitride luminescent materials, efforts
have mainly focused on the photoluminescence (PL) prop-
erties. To the best of our knowledge, their applications in
field emission displays (FEDs) have rarely been explored.[9]
Herein, we first reported a facile, low cost, and time-sav-
ing method for the synthesis of Y4Si2N2O7:Ce3+, Tb3+/Dy3+
phosphors using the Pechini-type sol–gel process followed
by the ammonolysis of the precursors. The Pechini sol–gel
method is a combination of the process of metal–complex
formation and in situ polymerization of organics. Normally,
a hydroxycarboxylic acid such as citric acid or salicylic acid
is used to form stable metal complexes, and their polyesteri-
fication with a polyhydroxy alcohol such as ethylene glycol
(EG) or poly(ethylene glycol) (PEG) forms a polymeric
resin. Immobilization of metal complexes in such rigid or-
ganic polymer networks reduces segregation of particular
metal ions, ensuring compositional homogeneity.[10] Com-
pared with the conventional solid-state reaction method,
the Pechini sol–gel method has the advantage of homogen-
Figure 1. XRD patterns of the Y4Si2N2O7:Ce3+, Tb3+, Dy3+ phos-
phors (a) and the coordination environments of Y atoms in the
Y4Si2N2O7 host (b).
eous mixing of the starting materials at the molecular level,
low synthetic temperature, good control of stoichiometry,
fine particle size, and uniform morphology.[11] The crystal
and electronic structures are studied and presented in this
The morphology of the crystalline Y4Si2N2O7 inspected
using a scanning electron microscope (SEM) is displayed in
Figure 2 (a). The sample consists of well-dispersed particles
with sizes ranging from 3–7 μm. In the HRTEM image –
Figure 2 (b) – the clear lattice fringes indicate the high crys-
tallinity of the as-prepared sample. The distance of
0.3072 nm between the adjacent fringes corresponds well
with the d031 spacing (0.3065 nm) of the pure Y4Si2N2O7
phase. The EDX spectrum analysis was carried out on the
Y4Si2N2O7 sample, as shown in Figure 2 (c). The results
confirm the presence of expected elements such as N, O, Si,
and Y in the Y4Si2N2O7 product. The quantificational ra-
paper. The PL and cathodoluminescence (CL) of Ce3+
,
Tb3+, and Dy3+ ions and the energy-transfer properties
from Ce3+ to Tb3+/Dy3+ in the Y4Si2N2O7 host under ultra-
violet light (UV light) and low-voltage electron beam exci-
tation have been discussed in detail.
Results and Discussion
Crystallization Behavior and Morphology
Figure 1 (a) shows the XRD patterns for
Y4Si2N2O7:Ce3+, Tb3+, Dy3+ phosphors. All the diffraction
peaks for Ce3+/Tb3+/Dy3+-doped Y4Si2N2O7 samples are in
good agreement with the JCPDS Standard Card no. 32-
1451 of Y4Si2N2O7, implying that the obtained samples are
single phase and adopt the same structure as the Y4Si2N2O7
host. The XRD patterns for the precursor of Y4Si2N2O7 (a)
and the sample obtained by sintering the precursor in air
(b) are presented in Figure S1. Accordingly, we can deter-
mine that the precursor for the Y4Si2N2O7 sample is the
mixed phase of Y2O3 and SiO2. This means that the silicates
did not form before the ammonolysis process. The phase of
the product can be determined to be Y2SiO5 after sintering
the precursor at 1200 °C in air. So, the NH3 atmosphere
plays an important role in preparing the desired oxonitrido-
silicates. In the Y4Si2N2O7 structure, there are four different
Y crystallographic sites Y(1), Y(2), Y(3), and Y(4), which
are coordinated by 6, 7, 7, and 7 O/N atoms.[12] The coordi-
nated structures are shown in Figure 1 (b). Because multiple
Figure 2. The SEM (a), HRTEM (b), and the EDX (c) of the
crystallographic sites can be substituted by the doped ions, Y4Si2N2O7 host.
Eur. J. Inorg. Chem. 2014, 1955–1964
1956
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
tion for the elements is listed in the inset in Figure 2 (c). prepared Y4Si2N2O7 sample has impressive thermal sta-
The results almost coincide with the theoretical calculation bility and antioxidation properties. In addition, Figure 4 (b)
of Y4Si2N2O7.
presents the XRD patterns for the product of the
Figure 3 shows the FTIR spectra for the precursor of the Y4Si2N2O7 sample after being sintered at 1000 °C for 2 h in
Y4Si2N2O7 (a), Y4Si2N2O7 (b), and Y2SiO5 (c) samples. The air. Compared with the JCPDS Standard Card no. 52-1810
precursor (a) was prepared by the Pechini sol–gel process of Y2SiO5 (black vertical line), the initial oxonitridosilicate
at a temperature of 750 °C. The Y4Si2N2O7 (b) and Y2SiO5 has been oxidized into Y2SiO5 at a temperature of 1000 °C.
(c) samples were obtained by treating the precursor at a If Y4Si2N2O7 is oxidized into Y2O3 + SiO2 or entirely
temperature of 1200 °C for 5 h in NH3 and in air, respec- Y2SiO5, the following relationship occurs, see Equation (1).
tively. All samples have a broad absorption band near
3439 cm–1, which could be assigned to the stretching vi-
bration of O–H bonds.[13] However, the shapes of spectra
below 1750 cm–1 for these samples are totally different. In
Figure 3 (a), the absorption band at 1507 cm–1 can be at-
tributed to the organic impurities that arise from the start-
ing materials such as citric acid and PEG.[14] The absorp-
tion bands of Si–O–Si (υas, 1095 cm–1; υs, 804 cm–1), Y–O
Oxidation in air
Y4Si2N2O7
Ǟ
(2Y2O3 + 2SiO2)/2Y2SiO5
(1)
(564 cm–1), and Si–O (δ, 470 cm–1) bonds (where υas
=
asymmetric stretching, υs = symmetric stretching, δ = bend-
ing) are also observed.[15] After being calcined at 1200 °C
for 5 h, the FTIR spectrum of the Y4Si2N2O7 sample [Fig-
ure 3 (b)] also shows many new absorption peaks located at
1141, 827, and 690 cm–1 compared with the Y2SiO5 sample
[Figure 3 (c)]. These may be attributed to Si–O(N) and
Y–O(N) bonds in the Y4Si2N2O7 sample.
Figure 4. TGA curves of the Y4Si2N2O7 sample (a) and the XRD
patterns of the Y4Si2N2O7 sample calcined at 1000 °C in air (b).
The theoretical increase of the weight is about 3.6%,
which is very close to the value (3.55%) obtained from the
TGA curve. Therefore, we could further confirm that the
molecular formula of the as-prepared product can be ex-
pressed by Y4Si2N2O7.
Band Structure and Density of States
As shown in Figure 5, calculations of the band structure
and density of states for pure Y4Si2N2O7 were carried out.
The results reveal that the pure Y4Si2N2O7 has an indirect
band gap of approximately 3.67 eV at point W, see Figure 5
(a). These calculations give information about the character
of the band gap.
Figure 3. FTIR spectra for the precursor (a), Y4Si2N2O7 (b), and
Y2SiO5 (c) samples.
In order to examine the thermal stabilities and further
The density of states (DOS) was calculated for each type
determine the composition of the as-prepared Y4Si2N2O7 of atom as well as for the entire compound, see Figure 5
sample, the thermogravimetric analysis (TGA) was carried (b). The conduction band is mainly composed of the Y 5d
out in air and under nitrogen. From the TGA curve in air – orbital, while the top of the valence band is mainly com-
see black line in Figure 4 (a) – it is found that the weight posed of the N 2p and O 2p orbitals, and the former has
of the product does not change significantly below 480 °C. more contributions. A similar result was reported earlier
From 480 to 920 °C the weight of the sample increases for LiBa5GaN3F5 where the transition occurred between a
gradually by about 3.55%. However, the weight of the sam- nitrogen dominated state and a hybrid nitrogen metal
ple remains almost unchanged at any temperature under state.[16] The diffuse reflection spectrum of Y4Si2N2O7 was
nitrogen, see red line in Figure 4 (a). So, we can conclude also measured (Figure 6). A strong absorption band around
that the powder has basically not been oxidized from room 220 nm can be observed, which corresponds to the band
temperature to 480 °C without an inert atmosphere (N2). transition in the Y4Si2N2O7 host lattice. With the extrapola-
However, the oxidation process became intensified as the tion of the linear region between 240 and 250 nm, the band
temperature rose to 920 °C. The results reveal that the as- gap was determined as 4.37 eV (234 nm). This value is
Eur. J. Inorg. Chem. 2014, 1955–1964
1957
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
tored at 441 nm consists of two separate bands in the region
from 260 to 380 nm, which can be attributed to the transi-
tions from the ground state to the different crystal field
splitting levels of the 5d state for the Ce3+ ions.[18] Under
UV excitation of 365 nm, the emission spectrum of the
Y4Si2N2O7:0.01Ce3+ sample displays an asymmetric emis-
sion band that ranges from 370 to 550 nm with a maximum
at about 441 nm, as shown in Figure 7. Because of the spin-
2
orbit splitting of the ground state (2F5/2 and F7/2) with an
energy difference of about 2000 cm–1, the emission spec-
trum for the Ce3+-doped phosphor usually has doublet
character.[19] In the Y4Si2N2O7:0.01Ce3+ sample, the emis-
sion band of Ce3+ ions consists of six well-separated
Gaussian components with peak centers at 413 nm, 441 nm,
460 nm, 475 nm, 498 nm, and 554 nm. Clearly, Ce3+ ions
occupy more than one crystallographic site in the Y4-
Si2N2O7 host. If there are several crystallographic sites in
the host, the activators can give preference for different sites
with various doping concentrations. Accordingly, the emis-
sion spectrum of the Y4Si2N2O7:Ce3+ sample was expected
to exhibit changeable profiles with different Ce3+ doping
concentrations. Figure 8 shows the emission spectra of
Figure 5. Band structure (a) and density of states (b) of the
Y4Si2N2O7 host.
larger than the calculated band gap (3.67 eV) due to the
insufficient description of the exchange correlation poten-
tial in the DFT calculations.[17]
Figure 7. Excitation and emission spectra as well as the representa-
tive Gaussian fitting bands of the emission spectrum for the
Y4Si2N2O7:0.01Ce3+ phosphor.
Figure 6. Reflection spectrum of the Y4Si2N2O7 host.
PL Properties
Y4Si2N2O7:Ce3+
Figure 7 shows the excitation and emission spectra of the
Y4Si2N2O7:0.01Ce3+ sample. The excitation spectrum
Figure 8. Various emission spectra of the Y4Si2N2O7:xCe3+ phos-
(black line) of the Y4Si2N2O7:0.01Ce3+ phosphor moni- phors with different Ce3+ doping concentrations.
Eur. J. Inorg. Chem. 2014, 1955–1964
1958
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Y4Si2N2O7:xCe3+ samples. Under the excitation of 365 nm,
the emission spectra of the Y4Si2N2O7:xCe3+ samples differ
with an increase in the concentration of Ce3+ ions. As
shown in the inset of Figure 8, the emission bands are red-
shifted with an increase in the doping concentration of
Ce3+. Obviously, the Ce3+ ions prefer to occupy the high
energy sites at a low doping concentration and they give
preference to low energy sites at high doping concentra-
tions. The PL intensity of Ce3+ as a function of its doping
concentration (x) in the Y4Si2N2O7:xCe3+ sample is shown
in Figure S2. The optimum doping concentration for Ce3+
in the Y4Si2N2O7 host is 1 mol-% of Y3+. In general, the
concentration quenching of luminescence is from the energy
migration amongst the activator ions at the high concentra-
tions. In the energy migration process the excitation energy
will be lost at a killer or quenching site, resulting in the
decrease of luminescence intensity.[20]
Y4Si2N2O7:Tb3+/Dy3+
As one of the most frequently used green emission acti-
vators in rare-earth-ion-doped luminescent materials, the
Tb3+ ions mainly show characteristic emissions resulting
5
from the transitions of D4 Ǟ7Fj (j = 6, ..., ..., 0).[21] The
excitation and emission spectra of Y4Si2N2O7:0.04Tb3+ are
shown in Figure 9 (a). The excitation spectrum monitored
Figure 9. Excitation and emission spectra of Y4Si2N2O7:0.04Tb3+
(a) and Y4Si2N2O7:0.01Dy3+ (b) phosphors.
5
by the D4 Ǟ7F5 transition of Tb3+ (545 nm) consists of a
broad band centered at 245 nm and several weak lines in
the region from 325 to 450 nm. The broad band is attrib-
uted to the spin-allowed transition from the 4f to the 5d emissions of Dy3+ ions. The excitation and emission spectra
state of the Tb3+ ion, and the weak lines arise from the of the Y4Si2N2O7:0.01Dy3+ phosphor are shown in Figure 9
forbidden fǞf transitions of the Tb3+ ion.[22] Under exci- (b). The excitation spectrum monitored by the emission of
4
tation at 245 nm, the emission spectrum of the the F9/2 Ǟ6H15/2 transition (483 nm) consists of a broad
5
Y4Si2N2O7:0.04Tb3+ phosphor consists of the D3,4 Ǟ7Fj band centered at 230 nm and several sharp peaks resulting
transitions of Tb3+ ions. As we know, the emission inten- from the f–f transitions of Dy3+ ions. According to the re-
sities of 5D3 Ǟ7Fj (blue emission) and 5D4 Ǟ7Fj (green flection spectrum of the Y4Si2N2O7 host, as shown in Fig-
emission) transitions depend strongly on the Tb3+ doping ure 6, the broad band in the excitation spectrum can be at-
concentrations. It can be attributed to the cross relaxation: tributed to the host absorption. So, we can deduce that the
5D3
+ +
7F6 Ǟ5D4 7F0, which can occur between the host can transfer energy to the Dy3+ ions in this system.
neighbor Tb3+ ions at a high doping concentration.[23] Fig- Upon excitation at 230 nm, the emission spectrum exhibits
ure S3 shows the emission spectra of the Y4Si2N2O7:yTb3+ two sharp peaks located at 483 and 576 nm from the
samples with different y at the excitation of 245 nm. The 4F9/2 Ǟ6H15/2 and F9/2 Ǟ6H13/2 transitions, respectively. In
4
blue emission is dominant at low Tb3+ concentrations addition, Figure S5(a) gives the diverse emission spectra of
(yϽ 0.01), while the green emission is predominant at high the Y4Si2N2O7:zDy3+ phosphor with different z values.
Tb3+ concentrations (yϾ 0.01). So, the emission color of With the increase of the Dy3+ concentration, the yellow
Y4Si2N2O7:Tb3+ phosphors can be tuned by changing the emission becomes stronger than the blue emission. Fig-
content of Tb3+ ions. Figure S4(a) shows the CIE chroma- ure S5(b) shows the emission intensity ratios (Y/B) of Dy3+
ticity coordinates of the Y4Si2N2O7:Tb3+ system with dif- ions in the Y4Si2N2O7 host. The increase of Y/B can be
ferent Tb3+ doping concentrations. Obviously, the emission ascribed to the following reasons. The first reason is reab-
color of Y4Si2N2O7:yTb3+ can be tuned from blue to green sorption. As shown in Figure 9 (b), there is an absorption
by simply altering the concentration of Tb3+ ions.
peak between 470 and 500 nm in the excitation spectrum
The Dy3+ ions have been chosen as an activator since it for the Dy3+ ion. As the concentration of Dy3+ ions in-
can emit yellow and blue light corresponding to the crease, the distance between Dy3+ ions becomes shorter, so
4
4F9/2 Ǟ6H13/2 and F9/2 Ǟ6H15/2 transitions, respectively.[24] the energy resulting from the 4F9/2 Ǟ6H15/2 (483 nm) transi-
4
4
The F9/2 Ǟ6H13/2 transition is hypersensitive and can be tion can be reabsorbed and then reemitted from F9/2
influenced by the surrounding chemical environment of the Ǟ6H13/2 (576 nm). Hence the blue emission becomes
Dy3+ ions in the host lattice,[24] so at a suitable lattice site, weaker and the yellow emission becomes stronger. The sec-
white light emission can be realized by the two color light ond reason is because of several crystallographic sites with
Eur. J. Inorg. Chem. 2014, 1955–1964
1959
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
different coordination environments. It is known that the
τ
ηT = 1 –
(2)
Dy3+ emission at 576 nm (4F9/2 Ǟ6H13/2) is an electric di-
pole transition, which is predominant only when Dy3+ ions
are located at low-symmetry sites with no inversion centers.
As the doping concentration of Dy3+ ions increases, there
will be a slight deviation from the symmetry in the host
because of the ionic radii difference between the Y3+ and
Dy3+ ions.[25] Hence, the yellow emission becomes stronger
than the blue emission and the emission color can be tuned
τ0
where τ0 and τ are the lifetimes of the sensitizer without
and with the activator, respectively. In the present system,
Ce3+ is the sensitizer and Tb3+/Dy3+ is the activator. Under
excitation at 365 nm, the energy-transfer efficiencies for
Ce3+ ǞTb3+ and Ce3+ ǞDy3+ can reach 51% and 39%
with y = 0.10 and z = 0.03, respectively. The emission color
of the Y4Si2N2O7:Ce3+, Tb3+/Dy3+ samples can be adjusted
from blue to green and from blue to bluish white, respec-
tively.
from blue-white to yellow-white by controlling the Dy3+
-
doping concentration. The CIE chromaticity coordinates of
Y4Si2N2O7:zDy3+ samples with different z values are shown
in Figure S4(b).
Y4Si2N2O7:Ce3+, Tb3+/Dy3+
As discussed above, the Tb3+ and Dy3+ ions can be cho-
sen as efficient activators for phosphors. However, the f–f
transitions of Tb3+ and Dy3+ ions are very weak and cannot
absorb UV light effectively. The 5d–4f transition of Ce3+ is
electric-dipole allowed and can strongly absorb UV light.
Fortunately, as shown in Figure S6(a) and (b), a spectral
overlap can be observed between the emission band of
Y4Si2N2O7:0.01Ce3+ and the excitation spectra of
Y4Si2N2O7:0.04Tb3+ as well as Y4Si2N2O7:0.01Dy3+, mak-
ing it possible to have an efficient energy transfer from Ce3+
to Tb3+/Dy3+. Figure S6(c) and (d) display the excitation
spectra of the co-doped Y4Si2N2O7: 0.01Ce3+, 0.01Tb3+
and Y4Si2N2O7: 0.01Ce3+, 0.01Dy3+ samples monitored
with the characteristic emissions of Tb3+ and Dy3+ ions,
respectively. The presence of Ce3+ absorption bands power-
fully supports the occurrence of the energy transfer between
Ce3+ and Tb3+/Dy3+ ions in the Y4Si2N2O7 host. Figure 10
(a) and (b) show selected emission spectra for
Y4Si2N2O7:0.01Ce3+
,
yTb3+ and Y4Si2N2O7:0.01Ce3+
,
zDy3+ samples for the excitation at 365 nm, respectively.
Clearly, the Tb3+ and Dy3+ ions can essentially be excited
by the Ce3+ excitation band through the energy-transfer
process. With a fixed concentration of Ce3+, the emission
intensity of Ce3+ decreased with increasing Tb3+/Dy3+ con-
centration, while the emission intensity of Tb3+/Mn2+ in-
creased with the increase of its concentration.
Figure 10. Variation of the emission spectra of the
Y4Si2N2O7:0.01Ce3+, yTb3+ (a) and Y4Si2N2O7:0.01Ce3+, zDy3+
(b) phosphors with different Tb3+ and Dy3+ doping concentrations.
The insets of (a) and (b) are the decay curves of Ce3+ monitored
The insets of Figure 10 (a) and (b) present the fluores-
cence lifetimes (τ) of Ce3+ monitored at 441 nm for the
at 441 nm in Y4Si2N2O7:0.01Ce3+, yTb3+ and Y4Si2N2O7:0.01Ce3+
,
=
Y4Si2N2O7:0.01Ce3+
,
yTb3+ and Y4Si2N2O7:0.01Ce3+
,
zDy3+ samples with different Tb3+ and Dy3+ concentrations (λex
zDy3+ samples with different Tb3+ and Dy3+ concentrations
(λex
365 nm). The obtained lifetimes of Ce3+ in
Y4Si2N2O7:0.01Ce3+ yTb3+ phosphors monitored at
365 nm).
=
,
441 nm were calculated to be 65.9, 54.7, and 32.6 ns with y
= 0, 0.01, and 0.10, respectively. And, the lifetimes of Ce3+
in the Y4Si2N2O7:0.01Ce3+, zDy3+ samples were 65.9, 57.1,
and 40.2 ns with z = 0, 0.005, and 0.03, respectively. We can
Temperature Quenching
It is generally required that phosphors for white LEDs
note that the decay lifetime of Ce3+ ions decreases with the should have low thermal quenching for avoiding the
increase of Tb3+ and Dy3+ content, which is convictive evi- changes in chromaticity and brightness of white LEDs.
dence for the energy transfer from Ce3+ to Tb3+ and Dy3+ Thus, thermal stability is one of the most important factors
ions in the Y4Si2N2O7 host. Generally, the energy-transfer that should be taken into consideration when preparing
efficiency (ηT) from the sensitizer to the activator can be phosphors for LEDs. As we know, phosphors used for
estimated by Equation (2)[26]
LEDs must sustain stable emission efficiency at a tempera-
Eur. J. Inorg. Chem. 2014, 1955–1964
1960
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
ture of about 150 °C over a long term.[27] Figure 11 (a) Cathodoluminescence Properties
shows the temperature-dependent emission spectra of the
The CL properties for Ce3+-, Tb3+-, and Dy3+-doped
Y4Si2N2O7 phosphors under the excitation of a low-voltage
electron beam have been investigated in detail. The
typical CL spectra for the Y4Si2N2O7:0.01Ce3+ (a),
Y4Si2N2O7:0.01Ce3+ sample. Clearly, the emission band po-
sition and the full width half maximum (FWHM) of the
emission spectra for the test sample are almost unchange-
able with the increase of the temperature (T = 300–500 K).
The emission intensities decrease with the increase of tem-
perature. At 423 K (150 °C), the emission intensity of the
Y4Si2N2O7:0.01Ce3+ sample remains 73% of the initial
emission intensity, as shown in Figure S7 in the Supporting
Information. The results indicate that Y4Si2N2O7:Ce3+
phosphors have low thermal quenching. The relationship
between temperature and luminescence intensity can be de-
scribed by the following expression[28]
Y4Si2N2O7:0.05Tb3+
Y4Si2N2O7:0.01Ce3+
(b),
Y4Si2N2O7:0.01Dy3+
0.03Tb3+
(d),
(c),
,
and
Y4Si2N2O7:0.01Ce3+, 0.01Dy3+ (e) phosphors are displayed
in Figure 12. For Ce3+/Tb3+/Dy3+ singly doped Y4Si2N2O7
phosphors, the typical emission of Ce3+ (blue), Tb3+
(green), and Dy3+ (blue-white) ions can be observed. The
CIE coordinates of these three samples are (x = 0.1564, y
= 0.1659), (x = 0.2842, y = 0.4520), and (x = 0.3074, y =
0.3385), respectively. The energy transfers from Ce3+ to
Tb3+ and Dy3+ in the Y4Si2N2O7 host have been found in
their co-doped samples. The emission intensity for Tb3+
and Dy3+ ions increased distinctly by introducing Ce3+ ions
into Y4Si2N2O7:Tb3+ and Y4Si2N2O7:Dy3+ samples with
the same doping concentration of Tb3+ and Dy3+. As ex-
pected, the tunable emission color can also be achieved un-
der the excitation of low-voltage electron beam. Figure 12
(d) and (e) show the representative CL spectra for
Y4Si2N2O7:Ce3+, Tb3+, and Y4Si2N2O7:Ce3+, Dy3+ phos-
ΔE
IT = I0[1 + c exp(– )]–1
(3)
kT
in which I0 and IT are the initial emission intensity and the
emission intensity at different temperatures, respectively; c
is a constant for a certain host; ΔE is the activation energy;
k is the Boltzmann constant (8.629ϫ10–5 eVK–1); and T is
the temperature. According to Equation (3), we present the
relationship between –ln[(I0/IT)–1] and 1/kT for the
Y4Si2N2O7:0.01Ce3+ sample, which is shown in Figure 11
(b). The ΔE of the Y4Si2N2O7: 0.01Ce3+ sample was calcu-
lated to be 0.203 eV.
phors.
The
CIE
chromaticity
coordinates
for
,
Y4Si2N2O7:0.01Ce3+, 0.03Tb3+ and Y4Si2N2O7:0.01Ce3+
0.01Dy3+ phosphors are (x = 0.1818, y = 0.2177) and (x =
0.2027, y = 0.2155), respectively.
Figure 12. CL spectra of the Y4Si2N2O7:0.01Ce3+ (a),
Y4Si2N2O7:0.05Tb3+
(b),
Y4Si2N2O7:0.01Dy3+
(c),
,
Y4Si2N2O7:0.01Ce3+
0.01Dy3+ (e) samples.
,
0.03Tb3+ (d), and Y4Si2N2O7:0.01Ce3+
Figure 13
(a)
shows
the
CL
intensity
of
and
Y4Si2N2O7:0.01Ce3+
,
Y4Si2N2O7:0.05Tb3+
,
Y4Si2N2O7:0.01Dy3+ samples as a function of accelerating
voltage. The CL intensities increase with increasing acceler-
ating voltage due to the deeper penetration of the electrons
into the phosphor, and thus more plasma will be produced,
which results in more activator ions being excited.[29] There
is no obvious saturation effect observed for the CL of these
Figure 11. Temperature-dependent emission spectra (a) and the
plots of –ln[(I0/IT) – 1] vs. 1/kT (b) for the Y4Si2N2O7:0.01Ce3+
phosphors.
Eur. J. Inorg. Chem. 2014, 1955–1964
1961
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
samples at higher accelerating voltages. The degradation be-
Conclusions
havior of the CL of the Y4Si2N2O7:0.01Ce3+ sample under
low-voltage electron beam excitation has been investigated.
For comparison, we measured the dependence of relative
CL intensity on the radiation time (0–120 min) for both
Y2SiO5:Ce3+ (commercial) and Y4Si2N2O7:0.01Ce3+ phos-
phors under the electron beam excitation, as shown in Fig-
ure 13 (b). The CL intensities for both Y2SiO5:Ce3+ and
Y4Si2N2O7:0.01Ce3+ phosphors decrease gradually with
prolonging the electron bombardment time. After con-
tinuous electron radiation for 60 and 120 min, the CL inten-
sity of the Y2SiO5:Ce3+ phosphor fell to 91.4 and 80.7% of
the initial value, respectively, while that for the
Y4Si2N2O7:0.01Ce3+ sample dropped to 90.6% and 79.2%
of the initial value, respectively. So, the Y4Si2N2O7:0.01Ce3+
sample has almost the same stability as the commercial
Y2SiO5:Ce3+ phosphor. The more stable products may be
obtained by improving the synthesis conditions. The ac-
cumulation of carbon at the surface of the samples during
electron bombardment may be responsible for the degrada-
tion of CL intensity.[30] Accretion of graphitic carbon will
prevent low-energy electrons from reaching the phosphor
grains and also exacerbate surface charging, which results
in less Ce3+ ions being excited and thus the CL intensity
decreases. Another reason for the decrease of the CL inten-
sity may be some permanent damage to the structure of the
phosphor after the electron bombardment for a certain
time. Although the emission intensity changes a lot, the
emission color for these two phosphors is nearly invariable
under continuous electron radiation for 2 h. The investiga-
tion of the degradation of CL for the Y4Si2N2O7:0.01Ce3+
phosphor indicates that the as-prepared samples have stable
CL intensity and CIE color coordinates under the electron
bombardment.
In summary, the single-composition phosphors
Y4Si2N2O7:Ce3+, Tb3+, Dy3+ have been prepared by a con-
venient, economical and energy-saving soft-chemical
method for the first time. The phase purity, crystallinity,
morphology, PL, and CL properties of Ce3+-, Tb3+-, and
Dy3+-activated Y4Si2N2O7 phosphors were discussed in de-
tail. The blue, green, and cyan emission can be obtained
from Ce3+, Tb3+, and Dy3+ single-doped Y4Si2N2O7 prod-
ucts, respectively. The tunable emission colors have been
achieved in Y4Si2N2O7:Tb3+ and Y4Si2N2O7:Dy3+ samples
by altering the doping concentrations of Tb3+ and Dy3+
ions. The energy transfers from Ce3+ to Tb3+ and Dy3+ ions
have been found and demonstrated through the PL spectra
and luminescence decay times of Ce3+ ions. Tunable emis-
sion from blue to green and cyan can be realized by energy
transfer and changing the doping concentrations of acti-
vators (Tb3+ and Dy3+) under the UV-light and low-voltage
electron beam excitation. The electronic structure of
Y4Si2N2O7 was investigated by density-functional theory
methods, which revealed that the nitrogen atom contributes
more excited electrons than the O atom. According to the
reflection spectrum of the Y4Si2N2O7 host, the band gap is
4.37 eV. Additionally, the impressive stability of the Y4S-
i2N2O7 host has been proved through temperature-depend-
ent PL properties and the degradation property of CL un-
der continuous electron bombardment. Thus, the
Y4Si2N2O7:Ce3+, Tb3+, Dy3+ phosphors may have many
applications in the field of UV W-LEDs and FEDs.
Experimental Section
Materials: Y2O3, Tb4O7, and Dy2O3 (99.999%) were purchased
from the Science and Technology Parent Company of Changchun
Institute of Applied Chemistry and other chemicals were purchased
from Beijing Chemical Company. All chemicals were of analytical
grade and used directly without further purification.
Preparation: A series of polycrystalline Y4Si2N2O7 and Ce3+-,
Tb3+-, Dy3+-doped Y4Si2N2O7 samples were prepared by the Pech-
ini-type sol–gel method followed by the ammonolysis of the precur-
sors. Typically, stoichiometric amounts of Y2O3, Tb4O7, and Dy2O3
were dissolved in dilute nitric acid (HNO3) whilst stirring and heat-
ing, resulting in the formation of colorless solutions of Y(NO3)3,
Tb(NO3)3, and Dy(NO3)3, respectively. First, stoichiometric
amounts of the solution of Y(NO3)3, Tb(NO3)3, Dy(NO3)3, and
Ce(NO3)3·6H2O were mixed together, stirred for 15 min, followed
by the addition of citric acid in the above solution (ratio citric acid/
metal ion = 2:1 in mol). Then, the pH of the solution was adjusted
to ca. 1 with HNO3 followed by adding the stoichiometric amount
of tetraethyl orthosilicate (TEOS), which was dissolved in ethanol.
Finally, a certain amount of polyethylene glycol (PEG, molecular
weight: 20000, A.R.) was added as a cross-linking agent (CPEG
=
0.01 molL–1) after stirring for several min. The resultant mixtures
were stirred for 2 h and then heated at 75 °C in a water bath until
homogeneous gels formed. After being dried in an oven at 100 °C
for 10 h, the gels were ground and prefired at 500 °C for 4 h in air.
Then the samples were fully ground and calcined at 750 °C in air
for 4 h. The obtained precursors were treated at a temperature of
Figure 13.
CL
intensity
of
Y4Si2N2O7:0.01Ce3+
,
Y4Si2N2O7:0.05Tb3+, and Y4Si2N2O7:0.01Dy3+ samples as a func-
tion of accelerating voltage (a) and dependence of relative CL in-
tensity of Y2SiO5:Ce3+ (commercial) and Y4Si2N2O7:0.01Ce3+ on
the radiation time under low-voltage electron beam excitation (b).
Eur. J. Inorg. Chem. 2014, 1955–1964
1962
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
C. Wang, Q. Wu, Y. Wang, J. Am. Ceram. Soc. 2013, 96, 1815–
1820; d) Y. Q. Li, N. Hirosaki, R. J. Xie, T. Takeda, M. Mi-
tomo, Chem. Mater. 2008, 20, 6704–6714; e) R.-J. Xie, N. Hiro-
saki, Sci. Technol. Adv. Mater. 2007, 8, 588–600; f) M. Zeuner,
S. Pagano, W. Schnick, Angew. Chem. Int. Ed. 2011, 50, 7754–
7775; Angew. Chem. 2011, 123, 7898; g) R.-J. Xie, H. T.
Hintzen, J. Am. Ceram. Soc. 2013, 96, 665–687; h) N. Zhong,
X.-S. Ning, K. Chen, M. Peng, Adv. Mater. Res. 2012, 412,
175–178.
a) R.-J. Xie, N. Hirosaki, N. Kimura, K. Sakuma, M. Mitom,
Appl. Phys. Lett. 2007, 90, 191101; b) H. Yang, Y. Liu, S. Ye,
J. Qiu, Chem. Phys. Lett. 2008, 451, 218–221; c) X.-M. Wang,
C.-H. Wang, M. M. Wu, Y. X. Wang, X.-P. Jing, J. Mater.
Chem. 2012, 22, 3388–3394.
a) J. W. H. van Krevel, H. T. Hintzen, R. Metselaar, Mater.
Res. Bull. 2000, 35, 747–754; b) T. Kurushima, G. Gundiah,
Y. Shimomura, M. Mikami, N. Kijima, A. K. Cheetham, J.
Electrochem. Soc. 2010, 157, J64–J68; c) M. Seibald, T. Rosen-
thal, O. Oeckler, F. Fahrnbauer, A. Tücks, P. J. Schmidt, W.
Schnick, Chem. Eur. J. 2012, 18, 13446–13452.
a) W. B. Park, Y. Song, M. Pyo, K.-S. Sohn, Opt. Lett. 2013,
38, 1739–1741; b) J. H. Ryu, H. S. Won, Y.-G. Park, S. H. Kim,
W. Y. Song, H. Suzuki, C. Yoon, Appl. Phys. A 2009, 95, 747–
752; c) N. Kimura, K. Sakuma, S. Hirafune, K. Asano, N. Hi-
rosaki, R.-J. Xie, Appl. Phys. Lett. 2007, 90, 051109; d) X. Li,
J. D. Budai, F. Liu, J. Y. Howe, J. Zhang, X.-J. Wang, Z. Gu,
C. Sun, R. S. Meltzer, Z. Pan, Light Sci. Appl. 2013, 2, e50.
a) C. Braun, M. Seibald, S. L. Börger, O. Oeckler, T. D. Boyko,
A. Moewes, G. Miehe, A. Tücks, W. Schnick, Chem. Eur. J.
2010, 16, 9646–9657; b) N. Hirosaki, R.-J. Xie, K. Kimoto, T.
Sekiguchi, Y. Yamamoto, T. Suehiro, M. Mitomo, Appl. Phys.
Lett. 2005, 86, 211905; c) R.-J. Xie, M. Mitomo, K. Uheda, F.-
F. Xu, Y. Akimune, J. Am. Ceram. Soc. 2002, 85, 1229–1234;
d) Y. Q. Li, J. E. J. van Steen, J. W. H. van Krevel, G. Botty,
A. C. A. Delsing, F. J. DiSalvo, G. De With, H. T. Hintzen, J.
Alloys Compd. 2006, 417, 273–279; e) K. Uheda, N. Hirosaki,
Y. Yamamoto, A. Naito, T. Nakajima, H. Yamamoto, Electro-
chem. Solid-State Lett. 2006, 9, H22–H25.
a) J. W. H. van Krevel, H. T. Hintzen, R. Metselaar, A. Meijer-
ink, J. Alloys Compd. 1998, 268, 272–277; b) Y. Menke, S.
Hampshire, L. K. L. Falk, J. Am. Ceram. Soc. 2007, 90, 1566–
1573; c) K. Inoue, N. Hirosaki, R.-J. Xie, T. Takeda, J. Phys.
Chem. C 2009, 113, 9392–9397.
a) Y. Q. Li, C. M. Fang, G. de With, H. T. Hintzen, J. Solid
State Chem. 2004, 177, 4687–4694; b) C. Chen, W. Chen, B.
Rainwater, L. Liu, H. Zhang, Y. Liu, X. Guo, J. Zhou, E. Xie,
Opt. Lett. 2011, 33, 1585–1590; c) C. J. Duan, A. C. A. Delsing,
H. T. Hintzen, J. Lumin. 2009, 129, 645–649.
1200 °C for 5 h in air or under an NH3 atmosphere to produce the
final silicates or oxonitridosilicates.
Characterization: The X-ray diffraction (XRD) measurements were
carried out with a D8 Focus diffractometer using Cu-Kα radiation
(λ = 0.15405 nm). Scanning electron microscopy (SEM) micro-
graphs and energy-dispersive X-ray (EDX) spectra were obtained
using a field emission scanning electron microscope (FE-SEM,
XL30, Philips). High-resolution transmission electron microscopy
(HRTEM) was performed using PEI Tecnai G2 S-Twin with a field
emission gun operating at 200 kV. Images were acquired digitally
with a Gatan multiple CCD camera. Fourier-transform Infrared
(FTIR) spectra were measured with a Vertex Perkin–Elmer 580BIR
spectrophotometer (Bruker) with the KBr pellet technique. Ther-
mogravimetry analysis (TGA) was carried out with a Netzsch STA
409 thermoanalyzer with a heating rate of 10 °Cmin–1 in air and
under nitrogen. The PL measurements were performed with a Hita-
chi F-7000 spectrophotometer equipped with a 150 W xenon lamp
as the excitation source. The density functional theory (DFT) cal-
culation for Y4Si2N2O7 was performed with the Vienna ab initio
simulation package (VASP).[31] The diffuse reflectance spectra were
taken with a Hatachi U-4100-Vis/NIR spectrophotometer. The
temperature-dependent (300–500 K) PL spectra were performed
with a fluorescence spectrophotometer equipped with a 450 W xe-
non lamp as the excitation source (Edinburgh Instruments, FLSP-
920) with a temperature controller. The CL measurements were [5]
carried out in an ultra-high vacuum chamber (Ͻ10–8 Torr), where
the phosphors were excited by an electron beam in the voltage
range of 2.5–5.0 kV and different filament currents, and the emis-
sion spectra were recorded using an F-7000 spectrophotometer.
The luminescence decay curves were obtained from a Lecroy Wave
Runner 6100 Digital Oscilloscope (1 GHz) using a tunable laser
(pulse width: 4 ns, gate: 50 ns) as the excitation (Continuum Sunlite
OPO).
[2]
[3]
[4]
Supporting Information (see footnote on the first page of this arti-
[6]
cle): XRD patterns of the precursor for Y4Si2N2O7 (a) and the
sample calcined at 1200 °C in air (b); emission intensity of Ce3+ as
a function of its doping concentration (x) in the Y4Si2N2O7:xCe3+
sample; emission spectra of Y4Si2N2O7:yTb3+ samples with dif-
ferent Tb3+ concentrations; CIE chromaticity coordinates of
[7]
Y4Si2N2O7:yTb3+ (a) and Y4Si2N2O7:zDy3+ (b) phosphors with
different Tb3+ and Dy3+ doping concentrations; emission spectra
(a) and the emission intensity ratios (Y/B) (b) of Y4Si2N2O7:zDy3+
samples with different z values; spectral overlap between the emis-
[8]
S. Thomas, J. Oró-Solé, B. Glorieux, V. Jubera, V. Buissette, T.
Le Mercier, A. Garcia, A. Fuertes, J. Mater. Chem. 2012, 22,
23913–23920.
T.-C. Liu, H. Kominami, H. F. Greer, W. Zhou, Y. Nakanishi,
R.-S. Liu, Chem. Mater. 2012, 24, 3486–3492.
J. Lin, M. Yu, C. K. Lin, X. M. Liu, J. Phys. Chem. C 2007,
111, 5835–5845.
a) M. Kakihana, J. Sol-Gel Sci. Technol. 1996, 6, 7–55; b) S. J.
Chen, X. T. Chen, S. Yu, J. M. Hong, Z. Xue, X. Z. You, Solid
State Commun. 2004, 130, 281–285.
sion band of Y4Si2N2O7:0.01Ce3+ and the excitation spectra of
Y4Si2N2O7:0.04Tb3+ (a) as well as Y4Si2N2O7:0.01Dy3+ (b), the ex-
citation spectra of Y4Si2N2O7:0.01Ce3+
,
0.01Tb3+ (c) and
[9]
Y4Si2N2O7:0.01Ce3+, 0.01Dy3+ (d) samples monitored with the
characteristic emissions of Tb3+ and Dy3+ ions; temperature depen-
dence of the emission intensity for the Y4Si2N2O7:0.01Ce3+ sample.
[10]
[11]
Acknowledgments
[12]
[13]
K. J. D. Mackenzie, G. J. Gainsford, M. J. Ryan, J. Eur. Ceram.
Soc. 1996, 16, 553–560.
This project is financially supported by the National Natural Sci-
ence Foundation of China (NSFC) (grant numbers 51332008,
51172227, 21221061), the Joint Funds of the National Natural Sci-
ence Foundation of China and Guangdong Province (grant number
U1301242), and the National Basic Research Program of China
(grant numbers 2010CB327704, 2014CB643803).
a) L. D. Carlos, C. de Mello Donegá, R. Q. Albuquerque, S.
Alves Jr., J. F. S. Menezes, O. L. Malta, Mol. Phys. 2003, 101,
1037–1045; b) G. Bühler, C. Feldmann, Angew. Chem. Int. Ed.
2006, 45, 4864–4867; Angew. Chem. 2006, 118, 4982; c) J. Hui,
Q. Yu, Y. Long, Z. Zhang, Y. Yang, P. Wang, B. Xu, X. Wang,
Chem. Eur. J. 2012, 18, 13702–13711.
[14]
a) M. Yu, J. Lin, Z. Wang, J. Fu, S. Wang, H. J. Zhang, Y. C.
Han, Chem. Mater. 2002, 14, 2224–2231; b) W. Xu, Y. Wang,
X. Bai, B. Dong, Q. Liu, J. Chen, H. Song, J. Phys. Chem. C
2010, 114, 14018–14024.
[1] a) F. C. Lu, X. P. Song, Q. L. Liu, Opt. Mater. 2010, 33, 91–
98; b) W.-T. Chen, H.-S. Sheu, R.-S. Liu, J. P. Attfield, J. Am.
Chem. Soc. 2012, 134, 8022–8025; c) Z. Yang, Z. Zhao, Y. Shi,
Eur. J. Inorg. Chem. 2014, 1955–1964
1963
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[15] a) J. Méndez-Vivar, A. Mendoza-Bandala, J. Non-Cryst. Solids
2000, 261, 127–136; b) M. Yu, J. Lin, J. Fang, Chem. Mater.
2005, 17, 1783–1791; c) Y. Xiao, D. Wu, Y. Jiang, N. Liu, J.
Liu, K. Jiang, J. Alloys Compd. 2011, 509, 5755–5760.
[16] F. Hintze, W. Schnick, Solid State Sci. 2010, 12, 1368–1373.
[17] F. Hintze, F. Hummel, P. J. Schmidt, D. Wiechert, W. Schnick,
Chem. Mater. 2012, 24, 402–407.
[18] a) W.-R. Liu, C.-H. Huang, C.-P. Wu, Y.-C. Chiu, Y.-T. Yeh,
T.-M. Cheng, J. Mater. Chem. 2011, 21, 6869–6874; b) Y. Liu,
X. Zhang, Z. Hao, Y. Luo, X. Wang, J. Zhang, J. Mater. Chem.
2011, 21, 16379–16384.
[19] a) P. Ghosh, A. Kar, A. Patra, Nanoscale 2010, 2, 1196–1202;
b) C. Duan, Z. Zhang, S. Rösler, S. Rösler, A. Delsing, J. Zhao,
H. T. Hintzen, Chem. Mater. 2011, 23, 1851–1861; c) D. Geng,
G. Li, M. Shang, D. Yang, Y. Zhang, Z. Cheng, J. Lin, J. Ma-
ter. Chem. 2012, 22, 14262–14271.
[20] a) Y.-C. Li, Y.-H. Chang, Y.-F. Lin, Y.-J. Lin, Y.-S. Chang,
Appl. Phys. Lett. 2006, 89, 081110; b) T. Grzyb, S. Lis, Inorg.
Chem. 2011, 50, 8112–8120; c) Y. Inaguma, T. Muronoi, K.
Sano, T. Tsuchiya, Y. Mori, T. Katsumata, D. Mori, Inorg.
Chem. 2011, 50, 5389–5395.
[21] a) D. Geng, G. Li, M. Shang, C. Peng, Y. Zhang, Z. Cheng, J.
Lin, Dalton Trans. 2012, 41, 3078–3086; b) Z. Mu, Y. Hu, H.
Wu, C. Fu, F. Kang, J. Alloys Compd. 2011, 509, 6476–6480;
c) S. Kubota, M. Izumi, H. Yamane, M. Shimada, J. Alloys
Compd. 1999, 283, 95–101.
[22] N. Guo, Y. Song, H. You, G. Jia, M. Yang, K. Liu, Y. Zheng,
Y. Huang, H. Zhang, Eur. J. Inorg. Chem. 2010, 4636–4642.
[23] a) K.-S. Sohn, Y. Y. Choi, H. D. Park, Y. G. Choi, J. Electro-
chem. Soc. 2000, 147, 2375–2379; b) K.-S. Sohn, N. Shin, Elec-
trochem. Solid-State Lett. 2002, 5, H21–H23.
[25]
[26]
R. D. Shannon, Acta Crystallogr., Sect. A 1976, 32, 751–767.
a) K. H. Kwon, W. B. Im, H. S. Jang, H. S. Yoo, D. Y. Jeon,
Inorg. Chem. 2009, 48, 11525–11532; b) G. Sinha, A. Patra,
Chem. Phys. Lett. 2009, 473, 151–154; c) S. Mandal, S. Bhatta-
charyya, V. Borovkov, A. Patra, J. Phys. Chem. C 2012, 116,
11401–11407; d) Y. Ruan, Q. Xiao, W. Luo, R. Li, X. Chen,
Nanotechnology 2011, 22, 275701.
a) R.-J. Xie, N. Hirosaki, T. Suehiro, F.-F. Xu, M. Mitomo,
Chem. Mater. 2006, 18, 5578–5583; b) C.-W. Yeh, W.-T. Chen,
R.-S. Liu, S.-F. Hu, H.-S. Sheu, J.-M. Chen, H. T. Hintzen,
J. Am. Chem. Soc. 2012, 134, 14108–14117; c) M. Krings, G.
Montana, R. Dronskowski, C. Wickleder, Chem. Mater. 2011,
23, 1694–1699.
a) Y. Huang, Y. Nakai, T. Tsuboi, H. J. Seo, Opt. Express 2011,
19, 6303–6311; b) Y.-C. Wu, D.-Y. Wang, T.-M. Chen, C.-S.
Lee, K.-J. Chen, H.-C. Kuo, ACS Appl. Mater. Interfaces 2011,
3, 3195–3199; c) J. Orive, R. Balda, J. Fernández, L. Lezama,
M. I. Arriortua, Dalton Trans. 2013, 42, 12481–12494.
[27]
[28]
[29] a) C. Feldman, Phys. Rev. 1960, 117, 455–459; b) D. Geng, M.
Shang, Y. Zhang, H. Lian, J. Lin, Inorg. Chem. 2013, 52,
13708–13718.
[30] a) C. Y. Duan, J. Chen, S. Z. Deng, N. S. Xu, J. H. Zhang,
H. B. Liang, Q. Su, J. Vac. Sci. Technol. B 2007, 25, 618–622;
b) X. G. Xu, J. Chen, S. Z. Deng, N. S. Xu, J. Lin, J. Vac. Sci.
Technol. B 2010, 28, 490–494.
[31] a) G. Kresse, J. Furthmüller, Comp. Mater. Sci. 1996, 6, 15–50;
b) G. Kresse, J. Hafner, Phys. Rev. B 1993, 47, 558; c) G. Kresse,
J. Hafner, Phys. Rev. B 1993, 49, 14251; d) G. Kresse, J.
Furthmüller, Phys. Rev. B 1996, 54, 11169.
Received: January 1, 2014
Published Online: March 5, 2014
[24] a) J. Lin, Q. Su, S. Wang, H. Zhang, J. Mater. Chem. 1996, 6,
265–269; b) J. Zhuang, X. Yang, J. Fu, C. Liang, M. Wu, J.
Wang, Q. Su, Cryst. Growth Des. 2013, 13, 2292–2297.
Eur. J. Inorg. Chem. 2014, 1955–1964
1964
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim