spectral properties and energy transfer of a potential solar energy converter
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Article
Spectral Properties and Energy Transfer of a Potential Solar Energy ConverterLei Zhou, Weijie Zhou, Fengjuan Pan, Rui Shi, Lin Huang, Hongbin Liang,
Peter A. Tanner, Xueyan Du, Yan Huang, Ye Tao, and Lirong Zheng
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b00763 • Publication Date (Web): 29 Mar 2016
Downloaded from http://pubs.acs.org on March 31, 2016
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Spectral Properties and Energy Transfer of a Potential Solar Energy
Converter
Lei Zhoua, Weijie Zhoua, Fengjuan Pana, Rui Shia, Lin Huanga, Hongbin
Liang,*a Peter A. Tanner* b, Xueyan Duc, Yan Huangc, Ye Taoc, Lirong
Zhengc
aMOE Laboratory of Bioinorganic and Synthetic Chemistry, State Key Laboratory of Optoelectronic
Materials and Technologies, School of Chemistry and Chemical Engineering, Sun Yat-sen University,
Guangzhou 510275, P.R. China.
E-mail: [email protected];
bThe Hong Kong Institute of Education (Education University of Hong Kong, designate), 10 Lo Ping
Road, Tai Po, Hong Kong S.A.R., P.R. China
E-mail: [email protected];
cBeijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of
Sciences, Beijing 100039, P.R. China
ABSTRACT: The energy transfer between Ce3+ and Eu2+ has been investigated in the host
Ca3Sc2Si3O12 (CSS), prepared by a modified sol-gel method. Excitation and emission measurements
from the near infrared to the vacuum ultraviolet spectral regions have been performed upon CSS,
Ce3+-doped CSS, Eu2+-doped CSS and Ce3+, Eu2+-co-doped CSS, at various concentrations, including
experiments at temperatures range of 15-460 K. The energy transfer efficiency from Ce3+ to Eu2+ can
approach 90% and the Ce3+ donor decay curves for different Eu2+ acceptor concentrations in the
co-doped system were fitted by the Inokuti-Hirayama method, indicating that it is energy transfer
induced by electric dipole interaction. The use of the Ce3+, Eu2+ couple in the CSS host as a wideband
harvester with an emission profile tailored to the response of the silicon solar cell in solar energy
conversion suffers from two main drawbacks relating to valence instability and emission quenching of
Eu2+. Possible solutions are suggested.
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1. INTRODUCTION
The World Energy Outlook 2015 released in November 20151 calls for the
understanding of the implications of the shifting energy landscape for economic and
environmental goals and for energy security. Oil price collapse, geopolitical
instability, trends in CO2 emissions and energy inefficiency all provoke us to seek
renewable and stable energy resources. Recent developments in flexible copper
indium gallium selenide,2 transparent solar cells,3 upconversion multicolor tuning4
and lanthanide ion-doped quantum dots5 provide optimism in this respect. Our goal
has been to harness as much of the solar flux as possible and herein we report a
wideband harvester with an emission profile tailored to the response of the silicon
solar cell.
The cubic silicate garnet host Ca3Sc2Si3O12 (CSS) is endowed with unique and
versatile spectroscopic properties. Its structure comprises Ca2+ in dodecahedral (8-)
and Sc3+ in octahedral 6-coordination to oxygen.6 Upon doping with Eu3+, the bands
of the transition 5D0 →7F4 located between 800-900 nm are unusually strong,
7
attributed to the selection rules for the distorted EuO8 coordination.8,9 The Tb3+-doped
CSS exhibits strong green luminescence with a lifetime of 3 ms and a rather slow
population of 5D4 from5D3.
7 The afterglow of the scintillator CSS:Pr 3+ can be
removed by co-doping with Mg2+ and hence the performance is improved.10 A
phosphor with color rendering index Ra > 90 for white light-emitting diode (wLED)
use was synthesized by co-doping CSS with Ce3+, Mn2+ and a charge-compensating
lanthanide ion.11 Perhaps the most striking property of the host is that it can extend the
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luminescence of divalent europium into the near infrared spectral region12 and this is
exploited in the present work.
The synthesis of the CSS host material may be problematic due to the presence
of various secondary phases when using solid state methods.6,8 Wu et al. have
proposed that the substitution of Sc3+ by Al3+ (below 40%) in CSS:Ce3+ in solid state
synthesis at 1450 oC can inhibit the formation of the impurity phases Sc2O3 and CeO2,
improve crystallinity, and enhance the photoluminescence intensity.13 Recently, a
freeze-drying method and increased heat treatment temperature have been utilized to
reduce the presence of secondary phases.14 The X-ray diffraction pattern of a sample
prepared by sol-gel combustion synthesis and subsequently fired at 1100 oC does not
exhibit other phases.15,16 Several candidates are available for the doping of this host
with divalent lanthanide ions, of which Eu2+ and Yb2+ are the most promising.17
The luminescence and excitation spectra of some Ce3+-activated silicate garnets
have previously been reported at room temperature.18,19 The Ce3+ electronic energies
were interpreted on the basis of two factors: the centroid shift from the free ion and
the 5d crystal field splitting. There have been numerous studies regarding of the
energy transfer between Ce3+ and Eu2+ in various solid-state hosts. To our knowledge,
the aim of these studies has been the development of near-ultraviolet-pumped white
light emitting diodes (wLEDs). For example, the Ca1.65Sr 0.35SiO4:Ce3+, Li+, Eu2+
phosphor has been recommended as a candidate for color-tunable blue-green
components of wLEDs, with emission between 465-550nm;20 Ba2ZnS3:Ce3+, Eu2+ has
application as a blue-converting phosphor for wLEDs, with emission maximum
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intensity at ~650 nm.21 The Ca4(PO4)2O:Ce3+, Eu2+ wLED phosphor has Eu2+
emission maximum at 650 nm.22
The format of this work is as follows. The structure and luminescence of the
host material, luminescence of Ce3+ or Eu2+-doped systems, and the energy transfer
from Ce3+ to Eu2+ in the CSS host material are presented and discussed in Section 2.
A comment is included in Section 3 concerning the applicability of Ce3+-Eu2+
co-doped CSS in the field of solar energy conversion. Some conclusions from the
experimental results and data analyses are made in the final Section 4.
2. RESULTS AND DISCUSSION
Ca2.54
Ce0.2
Eu0.06
Na0.2
Sc2Si
3O
12
Ca2.97
Eu0.03
Sc2Si
3O
12
Ca2.94
Ce0.03
Na0.03
Sc2Si
3O
12
Ca3Sc
2Si
3O
12
20 30 40 50 60 70 80
R e l a t i v e i n t e n s i t y ( a r b . u n i t s )
2θθθθ (degree)
ICDD PDF 2 card # 72-1969 Ca3Sc
2Si
3O
12
Figure 1. Representative XRD patterns of samples at room temperature.
2.1. Structure refinement. The X-ray diffraction (XRD) patterns of samples
Ca3-2 xCe x Na xSc2Si3O12 ( x = 0.001-0.2), Ca3- xEu xSc2Si3O12 ( x = 0-0.09),
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Ca2.8-2 xCe0.1Eu x Na0.1Sc2Si3O12 ( x = 0-0.09), Ca2.94-2 xCe xEu0.06 Na xSc2Si3O12 ( x = 0-0.2)
were measured at room temperature. The Na+ ions from Na2CO3 serve as charge
compensators for Ce3+. Figure 1 shows the X-ray diffraction patterns of some
representative samples. All of the samples were verified to comprise a single phase
and they are consistent with the standard file of Ca3Sc2Si3O12 (ICDD no.72-1969),
without other impurities such as Sc2Si2O7, Sc2O3, SiO2 and Ca2SiO4 etc. The
compound Ca3Sc2Si3O12 (CSS) crystallizes in the cubic system with the Ia-3d space
group (No. 230).13 In the structure, each Ca2+ is surrounded by 8 O2- ions to form a
distorted dodecahedron (D2 point symmetry) with four long Ca-O distances of
2.5660(14) Å and four short Ca-O distances of 2.4324(11) Å. Each Sc3+ is
coordinated with six equidistant oxygens at the distance of 2.1062(15) Å to form an
octahedron.13 The coordination environments are depicted in Figure S1. The crystal
data of CSS was used as the initial model for structural analysis and the rare earth ions
were assumed to be dispersed randomly in this host lattice. The refinement patterns of
the three representative samples (CSS host; CSS:0.03Ce; CSS:0.03Eu) were
processed using the software TOPAS23 and the results for the CSS host at room
temperature are shown in Figure S2, with the values of Rwp, R p, RB being in the range
of 2.1% - 4.4%, indicating a good fitting quality. Table S2 also presents the
crystallographic data and refined structure parameters for the three systems. The ionic
radii of eight-fold coordinated Ce3+ and Eu2+ are 114.3 and 125.0 pm,24 respectively,
so that it is suggested that Ce3+/Eu2+ occupy the Ca2+(VIII) (112.0 pm24) site because
of similar ionic sizes. In fact, Shimomura et al.6 have shown from X-ray absorption
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(λex = 206 nm; λem = 385 nm) at room temperature. (c) The excitation spectra (λem =
385 nm) at different temperatures.
2.2 The luminescence of Ca3Sc2Si3O12 host. The vacuum ultraviolet (VUV)
spectroscopy of pure Ca3Sc2Si3O12 was investigated as a prerequisite for the study of
the luminescence properties of doped samples. The emission spectrum upon
synchrotron radiation excitation at 206 nm and the VUV excitation spectrum by
monitoring at the wavelength of 385 nm emission at 15 K are shown in Figure 2(a). A
broad excitation band was observed with a maximum at 206 nm (6.02 eV) and is
associated with near-defect excitons. At higher energy, a broad shoulder band (184 nm,
6.74 eV) is present and is assigned to self-trapped exciton (STE) absorption. Upon
206 nm excitation, the emission exhibits a broad band with maximum at 385 nm. The
spectrum is similar to that reported by Ivanovskikh et al.26 who pointed out that the
broad emission band in the time-integrated excitation spectrum is attributed to
excitons localized near defects or to direct electron–hole recombination. These
authors also reported several other weak bands which are not present in Figure 2(a).
Figure 2(b) shows the monoexponential decay curve of the emission intensity I ,
fitted to Eq (1).
ln( I ) = ln A - kt (1)
where the slope k is the reciprocal of the intrinsic lifetime (τ0) and A is a constant.
The lifetime is fitted to be 5.5 µs. The decay is little slower than that previously
reported for CSS at 10 K (2 s27) and also in comparison with the decay time of
self-trapped exciton luminescence in pure LaCl3 (3.5 µs at room temperature28).
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Figure 2(c) shows the normalized excitation spectra of Ca3Sc2Si3O12 at different
temperatures between 15 K and 296 K. The shape and position of the band remain
unchanged relative to the situation at 15 K and are insensitive to temperature
variation.
100 200 300 400 500 600 700
λλλλem = 550 nm (UV)
λλλλem = 550 nm (VUV)
A
R e l a t i v e i n t e n s i t y
( a r b . u n i t s )
Wavelength (nm)
H
E
C
G
B
Ca2.8
Na0.1
Ce0.1
Sc2Si
3O
12 RT
F
D
λλλλex
= 440 nm
Figure 3.VUV-UV excitation spectra (λem = 550 nm) of Ca2.8Ce0.1 Na0.1Sc2Si3O12 and
the UV emission spectrum of Ca2.8Ce0.1 Na0.1Sc2Si3O12. The features in the excitation
spectrum at wavelengths longer than 350 nm are beyond the collection range of the
experimental setup at BSRF so that the excitation spectrum in the 280-530 nm range
was recorded with a spectrometer in our laboratory and normalized on the band D.
2.3. Spectra of Ca2.8Ce0.1Na0.1Sc2Si3O12 at room temperature (RT). The VUV-UV
excitation spectra of Ca2.8Ce0.1 Na0.1Sc2Si3O12 at room temperature are shown in
Figure 3. The far-left curve is the excitation spectrum using synchrotron radiation in
the 125-350 nm range when monitoring 550 nm emission of Ce3+. Six excitation
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bands (A-F) are distinguished in the 125-530 nm range as labeled in Figure 3. The
bands A (182 nm, 6.81 eV) and B (215 nm, 5.77 eV) are analogous to the exciton
absorptions observed in the VUV-UV excitation spectrum of Ca3Sc2Si3O12 in Figure 2,
but with different relative intensities and a red-shift of the latter by several nm. With
an excess of 8% for exciton binding energy,29 the band gap of CSS:Ce3+ is estimated
to be 7.35 eV at room temperature.
The three lower energy bands C (239 nm, 5.18 eV), D (308 nm, 4.02 eV) and F
(440 nm, 2.82 eV) are attributed to 4f-5d transitions of Ce3+, in line with previous
studies.12,30 In CSS-Ce the Ce3+ ion occupies the D2 symmetry Ca2+ site, so that the 5d
level is initially split into a lower doublet (Eg) and a higher triplet (T2g) by the cubic
component of the crystal field and then further split by the distortion from cubic
symmetry. A first-principles study27 has calculated the energies of the 4f 1 and 5d1
levels of Ce3+ in Ca3Sc2Si3O12 with different types of charge compensation
mechanisms. Assignments for the 5d(1)-5d(5) energy levels of Ce3+ in garnet host
lattices (mostly expressed as vibronic band maxima) are collected in Table 1 and in
the present case the assignments for 5d(1)-5d(3) appear secure. There is some
disagreement in the literature concerning the assignment of the higher 5d levels in
YAG:Ce3+. From the first principles calculation, the crystal field splitting (CFS) of
Ca3Sc2Si3O12:Ce3+
, Na+
is calculated to be about 27773 cm-1
(3.44 eV).
Table 1. Calculated (calc.) and observed (obs.) energies (in eV) for selected garnets
doped with Ce3+. Values refer to band maxima except for the calculation of Ref. 32 for
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YAG:Ce3+ which refers to zero phonon line energies. In YAG:Ce3+, the 5d(1) and 5d(2)
zero phonon lines are at 0.15 eV and 0.11 eV to low energy of the excitation band
maxima, respectively.32 Measurement temperatures are included, where appropriate.
Ref. System 5d(1) 5d(2) 5d(3) 5d(4) 5d(5)
This, 15 K, obs. Ca2.8Ce0.1 Na0.1Sc2Si3O12 2.82 4.03 5.19
12, 77 K, obs. Ca2.97Ce0.03Sc2Si3O12 2.79 4.03 5.23
27, calc. Ca3Sc2Si3O12:Ce3+, Na+ 2.87 3.94 5.59 6.10 6.31
31, obs./calc. Y3Al5O12:Ce3+ 2.71 3.65 5.50 ~5.50 6.06
32, calc. Y3Al5O12:Ce3+ 2.53 3.57 5.39 6.09 7.51
A discussion of the calculation of the centroid shift is included in the Supporting
Information and the calculated value is 1.42 eV (11455 cm-1). Hence, as also
remarked by Berezovskaya et al.,12 the observed relatively long-wavelength position
of the lowest 5d state for Ce3+ in CSS is attributed to the low 5d centroid shift energy
from the Ce3+ free ion level and the large crystal field splitting of the 5d1
configuration in this host (Figure S5).
In the emission spectrum of Ca2.8Ce0.1 Na0.1ScSi3O12 excited by 440 nm radiation
(Figure 3), a broad band with peak maximum at 505 nm and a shoulder at 550 nm are
observed, corresponding to the electronic transition from the relaxed lowest 5d state
to the 4f 1 J -multiplets 2F5/2 and2F7/2 of Ce
3+, respectively. Although there is a change
in total intensity of the emission bands, the shape and position are unchanged for
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excitation wavelengths in the range of 410-480 nm (Figure 4) so that is considered
that Ce3+ occupies only one crystal site: that of Ca2+, in CSS.
400 500 600 700
300
400
500
0
0.2
0.5
0.7
1.01300 400 500
0
10
20
30
40
Ca2.8Ce0.1Na0.1Sc2Si3O12 RT
300 400 500
0
50
100
150
I n t e n s i t y ( a r b . u n i t s )
5d(1)5d(2)
λλλλem
= 390 nm
λλλλem
= 550 nm
Wavelength (nm)Emission wavelength (nm)
E x c i t a t i o n w a v e l e n g t h ( n m )
5d(2)
5d(1)
Figure 4. The excitation spectra map of Ca2.8Ce0.1 Na0.1ScSi3O12 by monitoring
different emission wavelengths. The right-hand figures show the representative
excitation spectra by monitoring 390 and 550 nm emissions, respectively.
2.4. Spectral impurity bands in Ca2.8Ce0.1Na0.1ScSi3O12. The weak Band E (Figure
3: 330-360 nm) has not yet been assigned. This band is evident in the excitation
spectra of Liu et al.16 for CSS:Ce3+ samples prepared by the gel-combustion method
in air and by solid-state reaction method, but not in the spectrum of CSS:Ce3+
prepared by the gel-combustion method in carbon. The band was attributed by Ding et
al.27 to the second 4f → 5d transition of Ce3+, with Sc3+ substituting Si4+ in its local
environment. Our XANES shows that cerium is present in the 3+ oxidation state in
our samples (Figure S6). In order to further investigate whether the broad absorption
band E corresponds to defect or impurity absorption present beyond the limit of XRD
detection, the continuous excitation spectrum was recorded by monitoring the
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emission from 340 nm to 700 nm, as shown in Figure 4. The remarkable intense
absorption between 400 - 500 nm corresponds to the vibronic band of the 4f - 5d(1)
transition of Ce3+. The transition to 5d(2) shows weak absorption intensity (as marked
in Figure 4), whilst three additional weaker bands at 296, 330 and 360 nm appear
when monitoring emission at ~390 nm (Figure 4: top right-hand panel), which is at a
similar wavelength to that of the host emission (Figure 2). These excitation bands are
more prominent when monitoring the emission at 390 nm than at 550 nm, as shown
Figure 4, right-hand panels, Figure S7 and Figure S8. Furthermore, excitation at 330
nm or 360 nm gives an emission band ~390 nm in addition to the Ce3+ emission at
longer wavelength (Figure S9). The former emission band is shifted a few nm to
higher energy, at 385 nm, when exciting at 237 nm and 206 nm at 15 K (Figure S10).
The decay curves of the Ce3+ and defect site emissions are compared in Figure S11.
The life time of this defect site emission is 20±2 ns which is shorter than the 67 ns
decay of Ce3+. The defect sites may arise from aliovalent substitutions near Ce3+ ions
since their population leads not only to self-trapped excitonic emission but also to
Ce3+ emission. Since the relevant spectral features of these defect sites are at high
energy, their presence does not interfere with our study on Ce3+- Eu2+ energy transfer
and application.
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300 400 500 600 700
Ca3-2 x
Ce x Na
x Sc
2Si
3O
12 RT
N o r m a l i z e d i n t e n s i t y ( a r b . u n i t s )
Wavelength (nm)
x = 0.001
x = 0.03
x = 0.10
x = 0.15
x = 0.20
λλλλex
= 440 nm
λλλλem
= 550 nm
a
100 200 300 400 500
b
Time (ns)
λλλλex
= 440 nm, λλλλem
= 550 nm
Figure 5. (a) The normalized excitation spectra (λem = 550 nm) and emission spectra
(λex = 440 nm) for Ca3-2 xCe x Na xSc2Si3O12 ( x = 0.001-0.2) at room temperature. (b)
The corresponding decay curves of these samples.
2.5. Concentration and temperature dependence of Ce3+
emission in
Ca3-2 x Ce x Na x Sc2Si3O12. The effect of Ce3+ concentration upon the room
temperature emission spectrum (a) and lifetime (b) of CSS:Ce3+, Na+ is illustrated
in Figure 5. The increase in Ce3+ concentration markedly broadens features in the
excitation spectrum but exhibits a smaller effect upon the emission bands.
Notably, the defect site bands located at 330-360 nm are absent in the samples x =
0.001 and 0.03. It is remarkable that the Ce3+
lifetime remains monoexponential
and within the range of 67.0±0.7 for x = 0.001-0.1 (as also reported for CSS:Ce3+
by Shimomura et al.6), and only decreases to 62.6±0.1 for x = 0.2. This feature is
taken to indicate the absence of migration between Ce3+ ions and consequent
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photoluminescence of CSS:Ce3+ is far superior to that of the commercial phosphor
(Y,Gd)3Al5O12:Ce3+.
Figure S12 depicts the corresponding changes in the excitation spectrum of
Ca2.8Ce0.1 Na0.1Sc2Si3O12 when the temperature increases from 320 K to 480 K. The
5d(1) band broadens at low energies due to transitions from thermally-occupied
crystal field levels of 2F5/2. The defect site energy levels at 320-380 nm act as traps
and they are emptied with increasing temperature.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
VB
HS Ln2+
G
43
1
Lu
V R B E ( e V )
number of electrons n in Ln3+
4f n
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
2
5
Ln3+
E
Ln3+
G
LS
CB
Figure 7. VRBE scheme for lanthanide Ln3+ 4f n and 4f n-15d states (blue color), and
Ln2+ 4f n states (red color) in Ca3Sc2Si3O12. The excited energy levels of lanthanide
ions are taken from Refs. 33,34. Refer to the text for explanation.
2.6. Vacuum referred binding energy scheme (VRBE) scheme. The vacuum
referred binding energy (VRBE) scheme for Ln3+ 4f n and 4f n-15d states and Ln2+ 4f n
states in Ca3Sc2Si3O12 is displayed in Figure 7 by using published methods.33,34
Various approximations are involved, including the use of the same band gap for all
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ions, the use of band maxima instead of zero phonon line energies, and the separations
of high and low-spin states. The required data for the construction in the CSS host are
(i) the energy of the lowest 4f - 5d transition of Ce3+ (arrow 1: 2.84 eV); (ii) the host
band gap energy (arrow 2: 7.35 eV); (iii) the energy of the charge transfer band of
Eu3+ (arrow 3, see Figure S13: 4.86 eV); (iv) the Coulomb correlation energy, i.e.,
energy difference between the ground states of Eu2+ and that of Eu3+ (not shown, 6.93
eV); and (v) the centroid shift (Figure S5: 1.4 eV). The exchange splitting energy
between the low spin and high spin 4f - 5d transitions of Tb3+ in CSS is taken from
Velázquez et al.14 (arrows 4 and 5: 0.79 eV). The ground state of Eu2+ is found to be
above the Fermi energy level in Figure 7, indicating that the Eu2+ is unstable in this
host with respect to oxidation. This fact is supported by the calculated sum of the
bond valences (Eq. (1) in Ref. 35) coordinating Eu2+ in the CSS host (equal to the
oxidation number of Eu) and found to be 3.1 in the present case from the Ca-O bond
distances in CSS.
300 400 500 600 700 800 900 1000 1100 1200
λλλλex
= 405 nm, λλλλem
= 873 nm
Ca2.94
Eu0.06
Sc2Si
3O
12 RT
λλλλem
= 873 nm
Wavelength (nm)
R e l a
t i v e i n t e n s i t y ( a r b . u n i t s )
a
λλλλex
= 360 nm
λλλλex
= 520 nm
150 300 450 600 750 900 1050
Time (ns)
ττττ ~ 95.1 ns
b
Figure 8. (a) The excitation and emission spectra of Ca2.94Eu0.06Sc2Si3O12 at room
temperature. (b) The decay curve of Eu2+ emission in Ca2.94Eu0.06Sc2Si3O12 excited by
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a laser light source at room temperature.
2.7. Luminescence of Ca3- x Eu x Sc2Si3O12. The excitation and emission spectra of
Ca2.94Eu0.06Sc2Si3O12 at room temperature are shown in Figure 8(a). In this figure and
subsequently, the Eu2+ concentrations, x, are taken as the nominal amounts added in
the syntheses. A broad absorption band with maximum at 510 nm occupies the range
of 450-720 nm, with a stronger higher-energy band at 353 nm having a shoulder at
412 nm. These features correspond to the 4f 7→ 4f 65d transitions of Eu2+ ions. The
lower-energy band is derived from excitation to the 5d Eg orbital and 4f 6 core states
which are at lower energies than in Eu3+ since the divalent ion is larger. The
complexity of the energy levels in addition to the progressions in totally-symmetric
vibrational modes are responsible for the broad band. The higher-energy band
corresponds in addition to excitation to the 5d T2g orbital and 4f 6 core states. Upon
excitation at 360 nm or 520 nm (Figure 8a), a relatively intense band in the range
from 700 nm to 1100 nm is observed, with peak maximum at 873 nm. Low
temperature spectra taken at 13 K by varying the emission and excitation wavelengths
show similar spectral shape and position and are more clearly resolved than the room
temperature spectra (Figure S14). The emission band corresponds to the transition
from the lowest 4f 6
5d state to the 4f 7
ground state (8
S7/2) of Eu2+
.36
Note the absence
of Eu3+ emission. Dorenbos37 has given an empirical equation relating the energies of
the lowest 5d bands of Ce3+ and Eu2+. Using the energy of the Ce3+ emission band
(2.46 eV), the peak maximum for Eu2+ emission is estimated to be at 590 nm,
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700 800 900 1000 1100 1200
Ca3- x
Eu x Sc
2Si
3O
12 RT
R e l a t i v e i n t e n s i t y ( a r b . u n i t s )
Wavelength (nm)
873 nmλλλλ
ex = 520 nm
x = 0
x = 0.001
x = 0.01 x = 0.03
x = 0.06
x = 0.09
0.00 0.04 0.08
I n t e n s i t y
Concentration x
assuming the same Stokes shift, and this is far from the observed peak wavelength.
The decay curve of Eu2+ emission in Ca2.94Eu0.06Sc2Si3O12 was excited by 405 nm
radiation (Figure 8(b)) and can be well fitted by the monoexponential Eq. (1) with the
lifetime of 95.1 ns.
Figure 9. Emission spectra of the samples Ca3- xEu xSc2Si3O12 ( x = 0 – 0.09) at room
temperature. The inset shows the intensity-concentration dependence of emission.
Figure 9 displays the emission spectra for Ca3- xEu xSc2Si3O12, where x varies
from 0 to 0.09. The change of Eu2+ dopant ion concentration has negligible effect on
the location of the emission peak. The inset shows the luminescence intensity of
Ca3- xEu xSc2Si3O12 as a function of Eu2+
concentration x between 0 and 0.09 under 520
nm excitation at room temperature. With increasing Eu2+ concentration, the emission
intensity increases gradually and reaches a maximum when the Eu2+ concentration is x
= 0.06, after which quenching occurs. Figure S15 shows the corresponding excitation
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spectra which also exhibit the maximum intensity at x = 0.06. Therefore, in
Ca3- xEu xSc2Si3O12 the optimal doping concentration of Eu2+ is x = 0.06. In addition,
the decay curves for different doping contents x in Ca3- xEu xSc2Si3O12 (Figure S16) do
not show a significant lifetime change.
The temperature-dependence of the Eu2+ emission in Ca2.94Eu0.06Sc2Si3O12 is
rather unusual (Figure S17(a)). The emission intensity increases from 13 K up to 50 K
and then decreases. The initial increase is attributed to the thermal population of Eu 2+
excited states.38 A further increase in temperature produces photoionization. The Eu2+
ground state has been located in Figure 7 at 4.02 eV (from the CT transition of Eu3+).
The 4f – 5d zero phonon line energy of roughly 1.8 eV (Figure 8a) therefore places
the lowest Eu2+ 5d level at ~2.22 eV, i.e. ~0.66 eV (~5300 cm-1) below the conduction
band. The activation energy fit to T > 150 K in Figure S17(b) gives a linear plot with
the value of 0.05 eV (400 cm-1). Part of the discrepancy in value with 0.66 eV arises
from the uncertainty of location of the Eu2+ ground state (from the Eu3+ charge
transfer band maximum) and the band gap (from the excitation spectra, Figures 2(a), 3,
rather than from absorption measurements) and another part from the omission of
other parameters in the activation energy fit (see, for example, Ref. 38). However, it
can be concluded that the temperature stability of Eu2+ emission is poor.
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0.00 0.05 0.10 0.15 0.200.3
0.4
0.5
0.6
0.7
0.8
0.9
Ca2.94-2x
Cex Eu
0.06Na
x Sc
2Si
3O
12
R e
l a t i v e i n t e n s i t y
Ce3+
content (x)
(b)
350 400 450 500 550 600 650 700 750
0.2
0.4
0.6
0.8
1.0
1.2
Ca2.94-2 x
Ce x Eu
0.06Na
x Sc
2Si
3O
12
Wavelength (nm)
x = 0
x = 0.001
x = 0.03
x = 0.10
x = 0.20
λem
= 870 nm
N o r m a l i z e d i n t e n s i t y
RT
(a)
number of Ce3+ luminescence centers. By contrast, the emission intensity of Eu2+
increases up to x = 0.03 and then decreases. The variation of the integrated emission
areas for Ce3+ and Eu2+ is shown in the inner panel of the figure.
Figure 11. (a) The normalized excitation spectra (λem = 873 nm) of
Ca2.94-2 xCe xEu0.06 Na xSc2Si3O12 at room temperature. (b) Excitation intensity at 370 nm
relative to that at 520 nm.
The excitation spectra, normalized at 520 nm, of Eu2+ emission (λem = 873 nm)
from Ca2.94-2 xCe xEu0.06 Na xSc2Si3O12 at room temperature (Figure 11(a)) show a
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The energy transfer rates were estimated from the decay curves of the Ce3+:5d1→
4f 1 emission at 550 nm in Ca2.8- xCe0.1 Na0.1Eu xSc2Si3O12 ( x = 0-0.09) (Figure 12) at
room temperature. With ascending Eu2+ concentration, the lifetimes decrease
markedly and deviate from the monoexponential behavior of the sample x = 0.
Therefore, the curves were fitted by the double-exponential equation:
+
(2)
Where τ1 and τ2 are the fast and slow components of the luminescent lifetime,
respectively. A1 and A2 are the corresponding fitting parameters. The average lifetime
can be further evaluated by the following equation:
τ (τ + τ)( + ) (3)
The fitting results are presented in Table 2, with goodness of fit, for all the
samples. The Ce3+ lifetime is drastically reduced from 66.8 ns and follows a
monoexponential decay with Eu dopant ion concentration as shown in the top panel of
Figure 13. The linear relationship of k ET with Eu2+ dopant ion concentration x as
shown in the bottom panel of this figure indicates a direct transfer from Ce3+ to Eu2+,
with the transfer efficiency rising as high as 88.9% (Table 2, final column).
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Table 2. Lifetimes, fitting parameters, energy transfer rates and efficiency for
Ca2.8-2 xCe0.1 Na0.1Eu xSc2Si3O12 from measurements of Ce3+ emission at 295 K.
Eu2+
τ1 τ2 A1 A2 R2
adj τak ET (µs)
-1 η (%)
0 66.8 ± 0 66.8 ± 0 0.4874 0.4874 0.9984 66.8 0.0 0.0
0.001 18.0 ± 0.6 55.4 ± 0.5 0.2965 0.6886 0.9987 50.8 4.7 24.0
0.01 14.8 ± 0.3 48.1 ± 0.5 0.3855 0.5820 0.9984 42.4 8.6 36.5
0.03 6.9 ± 0.08 27.4 ± 0.2 0.5336 0.4332 0.9985 22.5 29.4 66.3
0.06 4.3 ± 0.04 17.1 ± 0.2 0.5995 0.2903 0.9985 12.8 63.4 80.9
0.09 2.6 ± 0.02 10.6±0.1 0.7053 0.2602 0.9990 7.4 120.4 88.9
ak ET = 1/τ - 1/τ0, where τ is the average lifetime at concentration x, and τ0 is at x =
0.001. η = 100(1 - τ/τ0).
0.00 0.02 0.04 0.06 0.08 0.100
20
40
60
E n e r g
y t r a n s f e r r a t e
k E T
( µ µµ µ s ) -
1
L i f e t i m e , τ ττ τ
( n s )
y = (52.9±6.7)exp[- x /(0.024±0.009)]+(7.2±6.2)
Ca2.8- x
Ce0.1
Eu x Na
0.1Sc
2Si
3O
12
RT
R 2
adj = 0.9395
0.00 0.02 0.04 0.06 0.08 0.10
0
40
80
120
R 2
adj = 0.9700
Ca2.8- x Ce0.1Eu x Na0.1Sc2Si3O12
Doping level, x
RTy ̀ = ( 1269±100) x ̀ - (2.6±4.6)
Figure 13. The Ce3+ emission lifetimes and the energy transfer rate as a function of
Eu2+ dopant ion concentration in Ca2.8-xCe0.1Eux Na0.1Sc2Si3O12.
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Table 3. The fitting parameters and the C A/C 0 ratios obtained from the I-H model.
Ca2.8- xCe0.1 Na0.1Eu xSc2Si3O12
C A(Eu2+
) Radj2 C A/C 0
0 0.9984 -
0.001 0.9839 0.34
0.01 0.9973 0.55
0.03 0.9944 1.31
0.06 0.8466 2.10
0.09 0.9806 2.94
Neglecting the value for x = 0.001 in Table 3, the average value of C 0, the critical
transfer concentration, is x = 0.025±0.006. Taking the intrinsic lifetime τ0 as 66.8 ns,
with the corresponding deactivation rate is 15 (µs)-1, then from the equation in the
lower Figure 13, the value of C 0 is calculated to be slightly lower at x = 0.014.
There are 8 x Eu2+ acceptors in the unit cell volume of 1837. 8 Å3, so that with
the use of Eq. 25 in Ref. 39:
300 4
3
RC
π
= (5)
the value of R0 is determined to be 13 Å. This critical transfer distance, R0, represents
the separation of an isolated Ce3+-Eu2+ pair when the energy transfer rate, k ET = 1/τ0,
i.e., the same rate as the spontaneous deactivation of Ce3+. The spectral overlap
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calculation in the Supporting Information gives the value of R0 as 25 Å.
Figure 14. Spectral conversion design for solar cell applications, involving the AM
1.5 solar spectrum, spectral response of c-Si, and the PLE and PL spectra of
Ca2.88Ce0.03Eu0.06 Na0.03Sc2Si3O12.
3. APPLICATION TO SOLAR CELLS
Figure 14 illustrates a schematic diagram for spectral conversion design in the solar
cell application of the phosphor CSS:Ce,Eu. The AM 1.5 solar spectrum commences
from the wavelength of 300 nm and shows the maximum absorption around 500 nm.
When sunlight falls, the photons are firstly absorbed by the phosphor layer and
converted to longer wavelengths more suitable for the response of the solar cell. The
presence of Ce3+ ions makes up for the smaller absorption of Eu2+ in the range of
400-450 nm, so that the excitation spectrum of the Ce3+
, Eu2+
co-doped sample
Ca2.88Ce0.03Eu0.06 Na0.03Sc2Si3O12 shows a continuous strong absorption from the UV
through the visible spectral range and matches very well with the incident solar flux,
implying a strong absorption of sunlight. Because the corresponding broad NIR
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emission is located in the region of highest spectral response of the c-Si solar cell, the
CSS: Ce, Eu phosphor could be a solar energy converter material for application
together with the c-Si photovoltaic solar cell. The energy transfer efficiency from Ce3+
to Eu2+ is nearly 90%. The two main drawbacks have been identified herein: the poor
valence stability of Eu2+ in the CSS host and the luminescence quenching with
temperature increase.
4. CONCLUSIONS
This study has comprised two facets: the spectral properties and energy transfer of
Ce3+ and Eu2+ in the garnet host and the suitability for solar energy harvesting. Indeed,
the CSS garnet host exhibits many unique characteristics. The energy levels of Ce 3+
are subject to a strong crystal field so that the 4f 1 -5d1 lowest energy zero phonon line
is located in the blue spectral region. The Ce3+ ion occupies the Ca2+ site and charge
compensation by Na+ has been included. The monoexponential emission decay does
not exhibit noticeable quenching for Ce3+ concentration below x = 0.2 in
Ca3-2 xCe x Na xSc2Si3O12, and the intensity only decreases by 20% at 460 K. By contrast,
the emission of Eu2+-doped CSS is more sensitive to concentration and temperature
quenching. However, the emission band is located in the near infrared spectral region
and broad, intense 4f 7
→ 4f 6
5d absorption bands span the visible and ultraviolet
regions. The spectral overlap between Ce3+ emission and Eu2+ absorption promotes
resonant energy transfer and the Ce3+ decay kinetics have been fitted by the
Inokuti-Hirayama formalism for electric dipole – electric dipole energy transfer, in
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agreement with the mechanism deduced from selection rules.
The broad, electric dipole allowed absorption spectrum of CSS:Ce3+, Eu2+
enables ~60% of the sunlight spectrum (from spectral overlap) to be utilized for solar
energy conversion. The emission is more intense than that of Nd3+ or Yb3+ systems
and it effectively targets the response of the c-Si solar cell. Although CSS:Ce3+ has
excellent emission intensity and thermal performance, the drawbacks of valence
instability and temperature quenching of emission when co-doping with Eu2+ have
been found. Some suggestions are included for research to solve these problems
which are related to host structure. First, the valence stability in a cubic garnet can be
tuned by variation of the central cation size and the introduction of larger cation sites
(e.g., Sr 2+, Ba2+) may be beneficial.41 The thermal instability due to photoionization
may be improved through the introduction of cations to improve structural rigidity
(e.g., Mg2+, Al3+, Ge3+); to increase the host bandgap;42 and to utilize core-shell
protected nanocrystals.43 A good host candidate could be Lu2CaMg2Si3O12, which
exhibits longer wavelength Ce3+ emission.44,45 It is also important to modify the form
of the solar cell device into a transparent glass or ceramic, or a phosphor in glass.46
We will pursue the above modifications.
ACKNOWLEDGMENTS
This work is financially supported by the National Natural Science Foundation of
China (21171176, U1232108, and U1432249).
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SUPPORTING INFORMATION
Experimental details; Centroid shift of Ce3+ in CSS; Energy transfer formulae; Figures
and Tables.
REFERENCES
(1) International Energy Agency, World Energy Outlook 2015,
http://www.worldenergyoutlook.org/weo2015/, sourced 19:30, 30 October 2015.
(2) Xu, M.;Wachters, A. J. H.; van Deelen, J.; Mourad, M. C. D.; Buskens, P. J. P. A
Study on the Optics of Copper Indium Gallium (di)Selenide (CIGS) Solar Cells with
Ultra-Thin Absorber Layers. Opt. Express, 2014, 22, A425-A437.
(3) Freitas, V. T.; Fu, L.; Cojocariu, A. M.; Cattoën, X.; Bartlett, J. R.; Le Parc,
R.; Bantignies, J.-L.; Wong, M. C. M.; André, P. S.; Rute A S Ferreira, R. A.
S.; Carlos, L. D. Eu3+-Based Bridged Silsesquioxanes for Transparent Luminescent
Solar Concentrators. ACS Appl. Mater. Interfac., 2015, 7 , 8770-8778.
(4) Wang, F.; Liu, X. Upconversion Multicolor Fine-Tuning: Visible to Near-Infrared
Emission from Lanthanide-Doped NaYF4 Nanoparticles. J. Am. Chem. Soc., 2008,
130, 5642-5643.
(5) Martín-Rodríguez, R.; Geitenbeek, R.; Meijerink, A., Incorporation and
Luminescence of Yb3+ in CdSe Nanocrystals. J. Am. Chem. Soc., 2013, 135,
13668–13671.
(6) Shimomura, Y.; Honma, T.; Shigeiwa, M.; Akai, T.; Okamoto, K.; Kijima, N.
Page 30
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-
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32/38
31
Photoluminescence and Crystal Structure of Green-Emitting Ca3Sc2Si3O12:Ce3+
Phosphor for White Light Emitting Diodes. J. Electrochem. Soc., 2007, 154, J35-J38.
(7) Piccinelli, F.; Speghini, A.; Mariotto, G.; Bovo, L.; Bettinelli, M. Visible
Luminescence of Lanthanide Ions in Ca3Sc2Si3O12 and Ca3Y2Si3O12. J. Rare Earths,
2009, 27 , 555-559.
(8) Bettinelli, M.; Speghini, A.; Piccinelli, F.; Neto, A. N. C.; Malta, O. L.
Luminescence Spectroscopy of Eu3+ in Ca3Sc2Si3O12. J. Lumin., 2011, 131,
1026-1028.
(9) Tanner, P. A. Some Misconceptions Concerning the Electronic Spectra of
Tri-Positive Europium and Cerium. Chem. Soc. Rev., 2013, 42, 5090-5101.
(10) Ivanovskikh, K. V.; Meijerink, A.; Piccinelli, F.; Speghini, A.; Ronda, C.;
Bettinelli, M. VUV Spectroscopy of Ca3Sc2Si3O12:Pr 3+: Scintillator Optimization by
Co-Doping with Mg2+, ECS J. Solid State Sci. Technol., 2012, 1, R127-R130.
(11) Liu, Y.; Zhang, X.; Hao, Z.; Wang, X.; Zhang, Tunable Full-Color-Emitting
Ca3Sc2Si3O12:Ce3+, Mn2+ Phosphor Via Charge Compensation and Energy Transfer.
Chem. Commun., 2011, 47 , 10677-10679.
(12) Berezovskaya, I. V.; Dotsenko, V. P.; Voloshinovskii, A. S.; Smola, S. S. Near
Infrared Emission of Eu2+ Ions in Ca3Sc2Si3O12. Chem. Phys. Lett., 2013, 585, 11-14.
(13) Wu, Y. F.; Chan, Y.H.; Nien, Y.T.; Chen, I.G. Crystal Structure and Optical
Performance of Al3+ and Ce3+ Codoped Ca3Sc2Si3O12 Green Phosphors for White
LEDs. J. Am. Ceram. Soc., 2013, 96 , 234-240.
(14) Velázquez, J. J.; Fernández-González, R.; Marrero-Jerez, J.; Rodríguez, V. D.;
ge 31 of 37
ACS Paragon Plus Environment
Chemistry of Materials
-
8/16/2019 Spectral Properties and Energy Transfer of a Potential Solar Energy Converter
33/38
-
8/16/2019 Spectral Properties and Energy Transfer of a Potential Solar Energy Converter
34/38
33
(21) Yang, W. J.; Chen, T. M. Ce3+/Eu2+ Codoped Ba2ZnS3: A Blue
Radiation-Converting Phosphor for White Light-Emitting Diodes. Appl. Phys. Lett.,
2007, 90, 171908 (1-3).
(22) Jia, Y.; Pang, R.; Li, H.; Sun, W.; Fu, J.; Jiang, L.; Zhang, S.; Su, Q.; Li, C.; Liu,
R.-S. Single-Phased White-Light-Emitting Ca4(PO4)2O:Ce3+,Eu2+ Phosphors Based
on Energy Transfer, Dalton Trans., 2015, 44, 11399-11407.
(23) Coelho A. TOPAS-Academic, Version 4.1; Coelho Software: Brisbane, Australia,
2007.
(24) Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of
Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr., 1976, 32,
751-767.
(25) Brown, I. D. Recent Developments in the Methods and Applications of the Bond
Valence Model. Chem. Rev., 2009, 109, 6858-6919.
(26) Ivanovskikh, K. V.; Meijerink, A.; Piccinelli, F.; Speghini, A.; Zinin, E. I.; Ronda,
C.; Bettinelli, M. Optical Spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and
Ca3Lu2Si3O12 Doped with Pr 3+. J. Lumin., 2010, 130, 893-901.
(27) Ding, W.; Wen, J.; Cheng, J.; Ning, L. X.; Huang, Y. C.; Duan, C. K.; Yin, M.
First-Principles Study of Ca3Sc2Si3O12: Ce3+ Phosphors. Chin. J. Chem. Phys., 2015,
28, 150-154.
(28) Van Loef, E. V. D.; Dorenbos, P.; and Van Eijk, C. W. E. The Scintillation
Mechanism in LaCl3:Ce3+. J. Phys.: Condens. Matter , 2003, 15, 1367-1375.
(29) Dorenbos, P. The Eu3+ Charge Transfer Energy and the Relation with the Band
ge 33 of 37
ACS Paragon Plus Environment
Chemistry of Materials
-
8/16/2019 Spectral Properties and Energy Transfer of a Potential Solar Energy Converter
35/38
-
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36/38
35
of Photoluminescence in Oxynitride Phosphors. J. Am. Chem. Soc., 2012, 134,
8022–8025.
(37) Dorenbos, P. Relation Between Eu2+ and Ce3+ f ↔ d Transition Energies in
Inorganic Compounds. J. Phys.: Condens. Matter , 2003, 15, 4797-4807.
(38) Duan, C.K.; Meijerink A.; Reeves R.J.; Reid M.F. The Unusual Temperature
Dependence of the Eu2+ Fluorescence Lifetime in CaF2 Crystals. J. Alloys Compd.,
2006, 408, 784-78.
(39) Inokuti, M.; Hirayama, F. Influence of Energy Transfer by the Exchange
Mechanism on Donor Luminescence. J. Chem. Phys., 1965, 43, 1978-1989.
(40) Henderson, B.; Imbusch, G. F. Optical Spectroscopy of Inorganic Solids,
Clarendon Press, Oxford. 1989. p. 448, Eqs. 10.9-10.12 and Figure 10.5, p. 458.
(41) Dorenbos, P. Valence Stability of Lanthanide Ions in Inorganic Compounds. Chem.
Mater., 2005, 17 , 6452-6456.
(42) Dorenbos, P. Determining Binding Energies of Valence-Band Electrons in
Insulators and Semiconductors via Lanthanide Spectroscopy. Phys. Rev. B, 2013, 87 ,
035118.
(43) Zhao, Y.; Rabouw, F. T.; van Puffelen, T.; van Walree, C. A.; Gamelin, D. R.; de
Mello Donegá, C.; Meijerink, A. Lanthanide-Doped CaS and SrS Luminescent
Nanocrystals: a Single-Source Precursor Approach for Doping. J. Am. Chem.
Soc., 2014, 136 , 16533–16543.
(44) Kishore, M. S.; Kumar, N. P.; Chandran, R. G.; Setlur, A. A. Solid Solution
Formation and Ce3+ Luminescence in Silicate Garnets. Electrochem. Solid State Lett.,
ge 35 of 37
ACS Paragon Plus Environment
Chemistry of Materials
-
8/16/2019 Spectral Properties and Energy Transfer of a Potential Solar Energy Converter
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36
2010, 13, J77-J80.
(45) Setlur, A. A.; Heward , W. J.; Gao, Y.; Srivastava, A. M.; Chandran, R.
G.; Shankar, M. V. Crystal Chemistry and Luminescence of Ce3+-Doped
Lu2CaMg2(Si,Ge)3O12 and its Use in LED Based Lighting. Chem. Mater., 2006, 18,
3314–3322.
(46) Huang, J.; Hu, X.; Shen, J.; Wu, D.; Yin, C.; Xiang, R.; Yang, C.; Liang, X.; Xiang,
W. Facile Synthesis of a Thermally Stable Ce3+: Y3Al5O12 Phosphor-in-Glass for
White LEDs. CrystEngComm, 2015, 17 , 7079-7085.
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Energy Transfer of a Potential Solar Energy Converter84x47mm (300 x 300 DPI)
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