NIR emission in Ba2SiO4:Eu2+, Nd3+ phosphors with near UV/violet excitation

Article abstract of DOI:10.1016/j.jallcom.2018.01.127

New results on NIR emission in Ba₂SiO₄:Eu²⁺, Nd³⁺ phosphors are reported. Though excitation for Eu²⁺ emission is in predominantly near UV (nUV) region, that for the Nd³⁺ emission around 106

Full text of DOI:10.1016/j.jallcom.2018.01.127

Accepted Manuscript
2+
3+
NIR emission IN Ba SiO :Eu , Nd phosphors with near UV/violet excitation
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4
Arpita Vyas, C.P. Joshi, P.D. Sahare, S.V. Moharil
PII:
S0925-8388(18)30128-2
10.1016/j.jallcom.2018.01.127
JALCOM 44591
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 19 November 2017
Revised Date: 8 January 2018
Accepted Date: 9 January 2018
Please cite this article as: A. Vyas, C.P. Joshi, P.D. Sahare, S.V. Moharil, NIR emission IN
2+
3+
Ba SiO :Eu , Nd phosphors with near UV/violet excitation, Journal of Alloys and Compounds
2
4
(2018), doi: 10.1016/j.jallcom.2018.01.127.
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NIR EMISSION IN Ba2SiO4:Eu2+, Nd3+ PHOSPHORS WITH NEAR UV/VIOLET
EXCITATION
Arpita Vyas1, C.P. Joshi1, P.D.Sahare2 and S.V. Moharil3
1 Physics Department, Shri Ramdeobaba College of Engineering and Management, Katol Road,
Nagpur 440013, India
2 Department of Physics and Astrophysics, University Of Delhi, North Campus, New Delhi
110007, India
3 Department of Physics, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur 440010,
India
ABSTRACT
New results on NIR emission in Ba2SiO4:Eu2+, Nd3+ phosphors are reported. Though
excitation for Eu2+ emission is in predominantly near UV (nUV) region, that for the Nd3+
emission around 1067 nm extends into visible region covering violet and blue part of the
spectrum. These results are highly significant for applications where NIR emission with
nUV/blue excitation is required, e.g. for improving efficiency of c-Si solar cell, for designing
NIR sources using efficient blue LEDs, etc. Energy transfer efficiencies for Eu2+ꢀ Nd3+ energy
transfer are estimated by measuring reduction of Eu2+ emission lifetime, and are close to 80 %.
Possible mechanisms for Eu2+ꢀ Nd3+ energy transfer are suggested. These involve down
shifting or quantum cutting.
Key Words: photoluminescence; NIR emission; silicate; Quantum Cutting; Eu2+ꢀ Nd3+ energy
transfer
*arpvyas@gmail.com
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1. Introduction
In the system BaO-SiO2 as many as thirteen phases are known [1]. Luminescence has
been studied in some of them and important phosphors have been discovered. Eu2+ activated
BaSi2O5 [2], Ba2Si3O8 [3], and Ba3SiO5 [4] are green emitting phosphors and have applications
in devices such as white-light-emitting diodes (W-LEDs). Pb-doped BaSi2O5 is a phosphor for
black-light lamp [5], whereas Ce3+ and Eu2+ doped BaSiO3 [6] generate blue-violet to yellow
light; a proper ratio leading to white light generation. Eu2+ and Dy3+ doped Ba3Si5O13 and
Ba5Si8O21 are stable even in water and exhibit long lasting phosphorescence (LLP) by exposure
to sunlight [7].
Barry [8] and Blasse et al [9] were the first to study Ba2SiO4:Eu phosphors. They
observed a broad emission band covering blue and green regions of the spectrum. Excitation
spectrum was also very broad; spread over almost entire UV region and extending into violet
part of the spectrum. Later, Poort et al [10] reported finer features of the PL spectra, e.g.
presence of two overlapping bands in the emission spectra which are responsible for the
observed large width. They attempted explanation of these specific features on the basis of the
crystal structure. They tried to resolve emission from Eu2+ at two crystallographically non-
equivalent sites on the basis of decay constants [11]. Grinberg et al [12] used high-pressure
spectroscopy for characterizing these sites. Zhang et al [13 14] suggested a method for
improving the stability of this phosphor. More recently, Lin et al [15] suggested use of this
phosphor as a scintillator. Broad excitation spanning 350-430 nm makes this phosphor suitable
for applications requiring near UV/blue excitation, such as solid state lighting [16-20]. Wang et
al [21] observed green long lasting phosphorescence (LLP) in this phosphor after nitrogen
doping. Xiaoye et al [22] observed significant increase in emission intensity by La3+/Y3+ co-
doping. This has been attributed to the defects introduced by the incorporation of trivalent ions.
Similar effects have been observed by Gd3+ [23], Li+ [24], Er3+ [25], Pr3+, Yb3+[26] co-doping. This
has been attributed to the defects introduced by the incorporation of aliovalent ions. Doping with
Zn has also resulted in enhanced emission intensity. However, this could be due to formation on
BaZnSi2O7 phase[27]. In contrast to this, luminescence enhancement by direct energy transfer to
Eu2+ is observed in Ba2SiO4: Ce, Eu [28]. Theoretical calculations have been made to estimate
effects of nitrogen [29] and Mn[30] co-doping on Ba2SiO4:Eu optical absorption. However, these
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estimates are far off from the experimental values. Apart from Eu2+, intense emission from Eu3+
has also been reported in Ba2SiO4 host [31].
In majority of works, conventional solid state reaction had been used for preparing
Ba2SiO4:Eu2+ phosphor. Han et al [32] suggested hydrothermal route for preparation of this
phosphor and claimed this to be simpler than the conventional solid state reaction. During recent
years different novel techniques have been used. These include sol–gel/Pechini [33], sol–gel
[34], co-precipitation [35 36], solution combustion [37], gas-solid phase hybrid synthesis method
[38], etc.
Broad nUV/blue excitation of Ba2SiO4:Eu2+ has been discussed in context of solid
state lighting. Apart from solid state lighting, such excitation is relevant for other applications
like modification of solar spectrum, luminescent solar concentrators (LSC) [39 40]
photoluminescence liquid crystal displays (PLLCD), etc. First two applications involve near
infrared (NIR) emission. c-Si solar cell is to date the most successfully commercialized solar
cell. One of the factors which limits efficiency of c-Si solar cell is the “spectral mismatch”, that
is spectral response curve for c-Si solar cell differs from solar spectrum. The mismatch can be
removed to some extent by converting the near UV and blue region of the spectrum, where solar
cell response is poor, to NIR region (around 1000 nm) by using suitable phosphors [41]. Trupke
et al predicted that if the light in the region 300-500 nm is converted to NIR using quantum
cutting, then the Shockley-Queisser limit for c-Si will be pushed from 29.5 to 39.6 % [42]. With
such efficiencies, cost of solar energy will be at par with the conventional energy sources.
There are not many, if any, reports on NIR luminescence in Ba2SiO4 host. For
obtaining NIR emission Yb3+ and Nd3+ ions are considered to be most suitable. Yb3+ has a simple
energy level diagram. There are only 2 levels; 2F5/2 and 2F7/2, separated by about 10150 cm-1. It is
thus most suitable for luminescence processes in NIR region around 985 nm. Since there are only
two levels there is no branching, all the emission must come through 2F5/2ꢀ 2F7/2 transition.
However, 2F7/2ꢀ 2F5/2 transition of Yb3+ ion is forbidden and hence very weak. CT band of Yb3+
is also usually at very high energies [43]. A sensitizer is needed for obtaining efficient NIR
emission. Paucity of energy levels often makes cooperative energy transfer as the only possible
process for sensitization. In contrast, owing to presence of large number of levels, sensitization
of Nd3+ is easily achievable. NIR emission in Nd3+ is very well known [44]. In fact, YAG:Nd is
one of the most important laser working in NIR region. For these reasons we attempted to obtain
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NIR emission using Yb3+ and Nd3+ dopants. In this work we report for the first time, NIR
emission in Ba2SiO4 resulting from efficient Eu2+ꢀ Nd3+ energy transfer.
2. Experimental
Ba2SiO4 phosphors doped with Eu2+, and Nd3+ or Yb3+ were prepared by solid state
reaction between barium carbonate and silicic acid (GR Loba, India). NH4Cl ( 2 wt %) was used
as a flux. BaCO3 was thoroughly mixed with stoichiometric amount of silicic acid. Eu/Nd/Yb
nitrate solutions in desired quantities were sprinkled on this mixture and then it was heated in the
furnace in 2 steps of 700 C for 4 hours, 1250 C for 6 hours. It was then slowly cooled to room
temperature. Eu/Nd/Yb nitrate solutions were obtained by dissolving europium
oxide/neodymium oxide (Indian Rare earths, 99.99 % pure)/ Yb2O3 (99.99 % pure, Rare Metals,
China) in dilute nitric acid. Samples prepared at 1250 C in air do not show Eu2+ luminescence.
For reducing europium to divalent form, the powders were heated in reducing atmosphere
provided by burning charcoal at 950 C for 2 hrs. This treatment was found adequate for
obtaining efficient PL.
The crystalline phases of the synthesized samples were identified by x-ray diffraction
(XRD) analysis. The XRD patterns were recorded on XPERT-PRO diffractometer using Cu Kα
(λ=1.54059 Ǻ) radiation. The NIR photoluminescence (PL) and photoluminescence excitation
(PLE) spectra were measured by a Photon Technology International QM-51 NIR
spectrophotometer. PL in visible range were recorded on Hitachi F-7000 spectro-fluorimeter.
Reflectance spectra were also recorded on the same instrument by using “synchronous” mode.
BaSO4 was used as a reference standard. Lifetime measurements were obtained on Horiba-JY
Fluromax 4- equipped with Time Correlated Single Photon Counting system using 379 nm LED
as excitation source.
3. Results and discussion
Formation of Ba2SiO4 host following the solid state reaction was confirmed by XRD.
Fig.1 shows comparison of the XRD pattern recorded for the synthesized Ba2SiO4 (undoped)
with ICDD file 70-2113. Excellent match is seen. Indexing is same as in the ICDD file and hence
not marked in Fig.1 to preserve clarity. For a BaO-SiO2 system, there are various phases
depending on the Ba/Si ratio. Three common phases are BaSiO3 [45], Ba2SiO4 [46], and Ba3SiO5
[47]. In the XRD pattern for the synthesized compound, lines at angles 24.118 and 36.464 which
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distinguish BaSiO3 (ICDD 70-2112), and Ba3SiO5 (ICDD 26-0180) respectively, are missing.
Phase pure Ba2SiO4 is thus formed. XRD patterns of doped samples were also similar and no
change in the structure was noticed.
Fig. 2 shows reflectance spectra for various samples. For Ba2SiO4, nearly 85%
reflectance is observed in the wavelength range of 500–600 nm, and then the reflectance starts to
decrease rapidly at shorter wavelengths. Two broad bands around 280 and 370 nm are due to
Eu2+. The host absorption edge is around 280 nm. These results are in good agreement with those
reported earlier [12]. After Nd co-doping, the graph remains almost similar. There is additional
absorption around 587 nm which can be assigned to 4I9/2--> 4G5/2 , 2H11/2 transitions of Nd3+.
Fig.3 shows PL spectra for Ba1.94Eu0.06SiO4. From literature, it was found that
maximum PL intensity is observed for 3% Eu and concentration quenching occurs for higher
doping concentration, hence this composition was chosen. Emission spectrum (Fig.3, curve a)
consists of a broad band peaking around 500 nm. The band is broad because it is superposition of
two bands as first mentioned by Poort et al [10]. Two bands arise from two types of Eu2+ centres.
In Ba2SiO4, Eu2+ will obviously occupy Ba substitutional site. Ba2SiO4 crystallizes in
orthorhombic system. There are two crystallographically non-equivalent sites. Fig. 4 shows unit
cell of Ba2SiO4 drawn using VESTA 3 software for three-dimensional visualization of crystal,
volumetric and morphology data [48]. Ba1 is ten coordinated while Ba2 nine [41]. Thus the
coordination of the Eu(I) and Eu(II) centres are ten and nine, respectively. According to Park et
al [49], the bond length of Eu(II)–O is shorter than that of Eu(I)–O, so the nephelauxetic effect
and the crystal field strength surrounding Eu(II) sites is greater than in the surrounding Eu(I).
Consequently, the Eu(I) and Eu(II) sites are responsible for emissions at the short (500 nm) and
long wavelengths (520 nm), respectively. Poort et al [10], on the other hand, argued on the basis
of second neighbor distances that the emission at shorter wavelengths can be expected from Eu2+
on Ba(II) site. It is difficult to decide between these two arguments, as in the recorded spectra
only one maximum can be observed. Two bands can be conjectured only after deconvolution
[49]. In the excitation spectrum (Fig.3, curve b), there is an intense band around 378 nm with a
shoulder around 280 nm. All these results are in good agreement with the literature.
Fig.5 shows PL spectra for Ba2SiO4:Eu2+ (3.0 mol %), Nd3+ (3.0 mol %) and
Ba2SiO4: Nd3+ (3.0 mol %) in NIR region. For doubly doped phosphor, a prominent emission is
seen for 400 nm excitation (curve a) around 1067 nm corresponding to transition 4F3/2ꢀ 4I11/2
.
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There are also weaker emission lines around 1010, 995, (4F3/2ꢀ4I11/2), 915, 909, 900,
4
(2P1/2ꢀ4F5/2), 887 nm(2D5/2ꢀ4F5/2, F3/2ꢀ4I9/2).
Fig.5 (curve b) shows excitation spectrum monitored at 1067 nm. A broad band
peaking at 400 nm, which is quite similar to Eu2+ excitation, but shifted slightly to longer
wavelengths, is again seen. This indicates energy transfer from Eu2+ to Nd3+. In addition to this,
there are several intense excitation lines attributable to f-f transitions of Nd3+ around 896,883,869
4
4
(4F3/2 ꢀ 2G9/2) 825 , (4I9/2 ꢀ 4F3/2), 809,799 (4I9/2 ꢀ F5/2, 2H11/2), 765, 754 (4I9/2 ꢀ F5/2,2H9/2),
743, (4I9/2 ꢀ 4F7/2), 722,725 (4I9/2 ꢀ 4S3/2), 673 (4I9/2ꢀ 4F9/2), 601 (4I9/2ꢀ 2K15/2), 587,576, (4I9/2
ꢀ 4G5/2 , 2H11/2), 529, (4I9/2 ꢀ 2K13/2, 4G7/2), 516, (4I9/2ꢀ 4G9/2) and 490 nm (4I9/2ꢀ 2K11/2). Due to
f-f excitation lines at shorter wavelengths, which overlap with Eu2+ broad band excitation, the
latter becomes broader and shifts slightly to longer wavelength side (Fig.6). It is also quite likely
that addition of Nd3+ causes small perturbations in Eu2+ levels. There is change in the physical
appearance of the samples after Nd3+ codoping. Nd3+ codoped samples present a richer hue. This
is due to more effective absorption in the visible region due to red shift of the excitation. For
Ba2SiO4: Nd3+ (3.0 mol %), only f-f lines are seen in the excitation spectrum, the broad band
around 400 nm is absent (Fig.5, curve e).
Inset to Fig.5 shows variation of intensities with Nd3+ concentration. PL intensity of
Nd3+ emission is highest for 3 mol. %. Concentration quenching is observed for higher
concentrations. From this the critical distance for Nd3+ -Nd3+ energy transfer can be calculated
using the formula [50].
Rc = 2 (3V/4πxcN)1/3
where xc is the critical concentration (.03), N is the number of Ba sites in the unit cell (8), and V
is the volume of the unit cell (445.5 Å3). Rc comes out to be 15.250 Å.
PL intensity of Eu2+ 500 nm emission goes on decreasing continuously with Nd3+
concentration. This indicates that Eu2+ꢀNd3+ energy transfer is not affected by concentration
quenching. However, Nd3+ emission is quenched beyond Nd3+ concentration of 3 mol. % due to
Nd3+ ꢀNd3+ energy transfer. Efficiency for Eu2+ ꢀNd3+ energy transfer can be estimated from
the formula [51]-
Iꢂꢃ
ηꢀꢁꢀ = 1 −
Iꢂꢃ,ꢄꢅ
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where Iꢂꢃ is the intensity of the Eu2+ emission without co-doping, and Iꢂꢃ,ꢄꢅ is the intensity after
co-doping with Nd3+. For Nd3+ concentration of 3 mol. %, where maximum Nd3+ emission is
observed ηꢀꢁꢀ comes out to be about 50%.
Efficiency for Eu2+ ꢀNd3+ energy transfer can also be estimated by measuring the
lifetime of Eu2+ emission with and without Nd3+ co-doping using a similar equation [47]
ηꢀꢁꢀ = 1 − ꢆꢆ
ꢇ
ꢈ
where τ0 is the lifetime of the Eu2+ emission without co-doping, and τx is the lifetime after co-
doping with Nd3+.
Fig.7 shows decay curves for 500 nm Eu2+ emission in Ba2SiO4:Eu2+,Nd3+ phosphors.
379 nm LED was used for excitation. For Ba2SiO4:Eu2+, lifetime of 0.52 ꢀs is observed. After
co-doping with Nd3+ another fast decay component with lifetime of about 110 ns is induced. This
component becomes more and more dominant with increasing Nd3+ concentration. For the
composition Ba1.88Eu0.06Nd0.06SiO4 the decay is almost exponential showing only this
component. Using this data ηꢀꢁꢀ comes out to be about 78.9%.
There is thus huge discrepancy in ηꢀꢁꢀ value when computed by two different
methods. The value obtained from intensity comparison can be much lower due to following
reason. When trivalent Nd3+ is added to Ba2SiO4:Eu2+, there can be two effects on Eu2+ emission
intensity. There will be obvious decrease due to energy transfer to Nd3+. However, substitution
of trivalent ions at Ba2+ sites also leads to formation of defects. These defects lead to increase in
Eu2+ emission. Considerable increase in Eu2+ emission following co-doping by trivalent
lanthanide ions have been observed by several workers [22 23 25 26]. The apparent decrease in
Eu2+ emission after Eu2+ꢀNd3+ energy transfer will be thus much less than the actual, which will
lead to much smaller value of ηꢀꢁꢀ
.
A possible mechanism of Eu2+ꢀNd3+ energy transfer will be now discussed. Nd3+
has several energy levels. Some of them (e.g. 4I9/2 --> 4G7/2) overlap with Eu2+ emission. Thus,
there are several channels for energy transfer from Eu2+to Nd3+. 4Gj levels of Nd3+ are populated
by energy transfer from Eu2+. Nd3+ can then relax to 4F3/2 state by emitting phonons in several
steps (Fig.8). NIR emission is obtained by transitions from 4F3/2 state to lower lying 4Ij states.
Another possibility is that energy transfer takes place directly from excited state of Eu2+ to
higher 4Gj states (4G11/2, 4G9/2). From there Nd3+ can de-excite to 4F3/2 level by cross relaxation
(Fig.9), taking a nearby Nd3+ ion to excited state. Subsequent de-excitation to ground state leads
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to emission of second photon. Thus, in this case two NIR photons will be obtained by quantum
cutting.
Apart from Nd3+, Yb3+ also can yield NIR emission. Yb3+emission is at relatively
shorter wavelengths and unlike Nd3+ there is no branching. Hence, we attempted
Ba2SiO4:Eu2+,Yb3+ phosphor for obtaining NIR emission. However, no such emission was
observed. Yb3+ has only two energy levels with separation of about 10150 cm-1. CT band of Yb3+
is also usually at very high energies, usually below 250 nm [43]. The only way energy in nUV
region can be transferred to Yb3+ is by cooperative energy transfer (CET), which is a less
probable phenomenon compared to energy transfer (ET). Apparently, no CET is taking place in
Ba2SiO4:Eu2+,Yb3+. In the past Nd3+-Yb3+ energy transfer had been reported [52-54]. Hence, we
studied triply doped Ba2SiO4:Eu2+,Nd3+,Yb3+ phosphor also. However, no Nd3+ꢀYb3+ energy
transfer was observed.
It will be interesting to measure the quantum efficiencies for NIR emission.
However, in this case the excitation is in nUV region and emission in NIR. A wide range
spectrofluorimeter that will enable seamless measurements of incident, reflected and emitted
light is needed for this purpose. Such experiments will be carried out in future and the results
will be presented in due course.
NIR emission in Ba2SiO4:Eu2+,Nd3+ phosphor with nUV/blue excitation can be
useful in several applications, solar photovoltaics being at the forefront.
Ba2SiO4:Eu2+,Nd3+ phosphor appears suitable for modification of solar spectrum. This is
illustrated in Fig.10. As can be seen, c-Si solar cell response decreases rapidly below 500 nm
(Fig.10, curve b). If this part of the spectrum (shown by yellow shaded region) is converted by
quantum cutting to about 1000 nm, efficiency of photovoltaic conversion will obviously
increase. There is good overlap between the solar spectrum suitable for quantum cutting, and
Eu2+ absorption. More than 50% of the spectrum available for quantum cutting will be converted
by Ba2SiO4:Eu2+,Nd3+ phosphor to Nd3+ emission that is close to the maxima in the response
curve of c-Si.
Apart from solar photovoltaics, Ba2SiO4:Eu2+,Nd3+ phosphor could be useful for
obtaining compact NIR light sources. Efficient blue LEDs are commercially available.
Ba2SiO4:Eu2+, Nd3+ phosphor shows appreciable excitation around 450 nm. By coating it on blue
LED, compact, intense and efficient LED emitting in NIR region can be constructed.
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4. Conclusions:-
New results on luminescence of Ba2SiO4:Eu2+,Nd3+ are reported. Efficient
energy transfer from Eu2+ꢀNd3+ has been observed. Critical distance for Nd3+ ꢀNd3+ energy
transfer is 15.25 Å. Lifetime of Eu2+ emission decreases from 0.52 ꢀs to 0.11 ꢀs following
Nd3+co-doping. Efficiency for Eu2+ ꢀNd3+ energy transfer is close to 80 %. By virtue of this
energy transfer it is possible to convert nUV-blue light around 350-450 nm to NIR around 1067
nm. This phosphor thus holds a great potential for application as a solar spectrum modifier. In
contrast to Eu2+ ꢀNd3+ pair, no energy transfer is observed for Eu2+ ꢀYb3+ or Nd3+ ꢀYb3+
pairs.
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-REFERENCES-
[1] Liudmila A.Gorelova, RimmaS.Bubnova, Sergey V.Krivovichev, Maria
G.Krzhizhanovskaya, Stanislav K.Filatov J. Solid State Chem. 235 (2016) 76
[2] J.H.Park, J.S.Kim and J.T.Kim J.Opt.Soc. Korea 18 (2014) 45
[3] F.Xiao, Y.Xue and Q.Zhang, Spectro chim.Acta A:Mol. Biomol.Spectrosc.74 (2009) 758
[4] J.Park, M.Lim, K.Choi and C.Kim, J.Mater.Sci.40 (2005) 2069
[5] J.W.Chung, H.K.Yang, B.K.Moon, B.C.Choi and J.H.Jeong, J.Korean Phys. Soc. 55 (2009)
1965
[6] C.Guo, Y.Xu, Z.Ren and J.Bai, J.Electrochem.Soc.158 (2011) J373
[7] P.Wang, X.Xu, D.Zhou, X.Yu and J.Qiu, Inorg.Chem.54 (2015) 1690
[8] T.L. Barry, J. Electrochem. Soc. 115 (1968) 1181
[9] G. Blasse, W.L. Wanmaker, J.W. Tervrugt and A. Bril, Philips Res. Rep. 23 (1968) 189
[10] S.H.M. Poort, W. Janssen, G. Blasse, J. Alloys Compd. 260 (1997) 93
[11] S.H.M. Poort , A.Meyerink and G. Blasse J.Phys. Chem. Solids 58 (1997) 1451
[12] M.Grinberg, J. Barzowska, A. Baran, and B. Kuklínski, Materials Science- Poland, 29
(2011) 272
[13] B.Zhang, J.W. Zhang, H. Zhong, L.Y.Hao, X. Xu, S. Agathopoulos, C.M. Wang and L.J.
Yin, Mater. Res. Bull., 92 (2017) 46
[14] B.Zhang, J.W. Zhang, H. Zhong, L.Y.Hao, X. Xu, S. Agathopoulos, C.M. Wang and L.J.
Yin, J. Phys. Chem. C, 121 (2017)11616
[15] Litian Lin, Xiaoxiao Huang, Rui Shi, Weijie Zhou, Yan Huang, Jiuping Zhong, Ye Tao,
Jun Chen, Lixin Ning and Hongbin Liang RSC Adv. 7 (2017) 25685
[16] M. Venkataravanappa, H. Nagabhushana, G.P. Darshan, S.C. Sharma, K.V. Archana, R.B.
Basavaraj and B.D.Prasad, Mater. Res. Bull.97, (2018) 281
[17] J.S. Kim, Y.H. Park, S.M. Kim, J.C. Choi and H.L. Park Solid State Commun., 133
(2005) 445.
[18] J.S. Kim, P.E. Jeon, J.C. Choi and H.L. Park Solid State Commun., 133(2005) 187.
[19] M. Zhang, J. Wang, Q. Zhang, W. Ding and Q. Su, Mater. Res. Bull. 42 (2007) 33
[20] Z. Wang, S. Guo, Q. Li, X. Zhang, T. Li, P. Li, Z. Yang, Q. Guo, Physica B: Condensed
Matter, 411 (2013) 110
10

ACCEPTED MANUSCRIPT
[21] M.Wang, X. Z.Hang, Z.Hao, X.Ren, Y.Luo, X.Wang and J. Zhang, Opt. Mater. 32 (2010)
1042
[22] H. Xiaoye, L. Zhenhua, X. Xin and L. Yongxiu, J. Rare Earths 27 (2009) 47
[23] X. Li, Y. Liang, F. Yang, Z. Xia, W.Huang and Y. Li, J. Mater. Science: Materials in
Electronics, 24 (2013) 3199
[24] D. Kim, K.W. Jeon, J.S. Jin, S.G. Kang, D.K. Seo and J.C. Park, RSC Advances, 5 (2015)
105339
[25] L.L. Luo, K. Tang, D.C. Zhu, T. Han and C. Zhao, Acta Physica Sinica, 62 (2013) 157802
[26] D. Zhong, X.Hu, Z. Li and Y.J. Li, Chinese Rare Earth Soc., 27 (2009) 36
[27]Y. X. Pan and G. K. Liu Spectroscopy Letters, 44 (2011) 1
[28] H.L.Liu, D.W. He and F. Shen, Spectroscopy and Spectral Analysis, 26 (2006) 1790
[29] H.Chen, X.Huang, W.Huang and W. Wang, Optik, 134(2017)78
[30] H.Chen, X.Huang and W.Huang Chinese J. Physics, 54 (2016) 931
[31]A.M.Pires, M.R.Davolos and O.L.Malta, J. Lumin. 72-74 (1997) 244
[32] J.K. Han, M.E. Hannah, A. Piquette, J.B. Talbot, K.C. Mishra and J. McKittrick, J. Lumin.
161 (2015) 20
[33] J. K. Han, M. E. Hannah, A. Piquette, J. Micone, G. A. Hirata, J. B.Talbot, K. C. Mishra
and J. Mckittrick, J. Lumin. 133 (2013) 184
[34] A. Birkel, N. A. DeCino, N. C. George, K. A. Hazelton, B.-C. Hong and R. Seshadri, Solid
State Sci. 19 (2013) 51
[35] J. K. Han, M. E. Hannah, A. Piquette, J. B. Talbot, K. C. Mishra and J. Mckittrick, ECS J.
Solid State Sci. Technol. 1 (2012) R98
[36] J. S. Lee and Y. J. Kim Ceram. Int. 39 S555 (2013)
[37] Huayna Cerqueira Streit, Jennifer Kramer, Markus Suta and Claudia Wickleder Materials,
6 (2013) 3079
[38] Tatsuya Sakamoto, Kazuyoshi Uematsu, Tadashi Ishigaki Kenji Toda and Mineo Sato Key
Engineering Materials 485 (2011) 325
[39] W.G.J.H.M.van Sark, etal. Optics Express 16 (2008) 21773
[40] C.J. Barrows , P. Chakraborty , L.M. Kornowske and D.R. Gamelin ACS Nano 10
(2016) 910
11

ACCEPTED MANUSCRIPT
[41] M.B. de la Mora, O. Amelines-Sarria, B.M. Monroy, C.D. Hernandez-Perez and J.E. Lugo
Solar Energy Mater. Solar Cells 165 (2017) 59
[42] T. Trupke, M. A. Green and P. Wurfel J. Appl. Phys. 92(2002) 1668
[43] L. van Pieterson, M. Heeroma, E. de Heer and A. Meijerink, J.Lumin 91 (2000) 177
[44] K. Lemanskin, M.Babij, M.Ptak and P.J.Deren J. Lumin. 184(2017)130
[45] H. P. Grosse and E. Tillmanns, Cryst. Struct. Commun. 3 (1974) 603
[46] H.P. Grosse and E. Tillmanns, Cryst. Struct. Commun. 3 (1974) 599
[47] E. Tillmanns and H. P. Grosse Acta Cryst. B34 (1978) 649
[48] K. Momma and F. Izumi: J. Appl. Crystallogr. 44 (2011) 1272
[49] Jung Hye Park, Wonsik Ahn and Young Jin Kim J. Nanosci. Nanotechnol.15 (2015) 8155
[50] G. Blasse Philips Res. Rep. 24 (1969) 131
[51] P.I. Paulose, G. Jose, V. Thomas, N.V. Unnikrishnan and M.K.R. Warrier J. Phys. Chem.
Solids, 64 (2003) 841
[52] A.A. Pathak, R.A. Talewar, C.P. Joshi, S.V. Moharil Opt.Mater. 64 (2017) 217
[53] Ting Sun, Ai-Hua Li, Chao Xu, Yu-Heng Xu and Rui Wang Opt. Laser Tech.56 (2014)
322
[54] Flavia Artizzu, Angela Serpe, Luciano Marchio, Michele Saba, Andrea Mura, Maria Laura
Mercuri, Giovanni Bongiovanni, Paola Deplano and Francesco Quochi J.Mater.Chem. C 3
(2015) 11524
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-FIGURE CAPTIONS-
Figure 1 XRD pattern for Ba2SiO4
A good match with ICDD 70-2113 is seen. Lines at angles 24.118 and 36.464 which distinguish
BaSiO3 (ICDD 70-2112), and Ba3SiO5 (ICDD 26-0180), respectively, are absent.
Figure 2 : Reflectance spectra of Ba2SiO4
a> Ba1.94Eu0.06SiO4
b> Ba1.88Eu0.06Nd0.06SiO4
Figure 3 : PL spectra for Ba1.94Eu0.06SiO4 phosphor
a> Emission for 400 nm excitation.
b> Excitation for 500 nm emission
Figure 4 : Unit cell of Ba2SiO4 showing different cation coordination.
There are two types of Barium sites. Ba1 has 10 coordination while Ba2 nine.
Figure 5 : PL spectra for Ba1.88Eu0.06Nd0.06SiO4
a> Emission for 400 nm excitation.
b> Excitation for 1067 nm emission
Inset shows variation of Nd3+ emission (1067 nm, curve c) and Eu2+ emission (500 nm, curve d)
with Nd3+ concentration. Excitation was 400 nm.
For comparison, PL excitation for Ba1.94Nd0.06SiO4 is shown (curve e).
Figure 6 : Broadening of excitation spectra after Nd3+ co-doping in Ba1.88Eu0.06Nd0.06SiO4
a> Excitation spectrum for 500 nm emission
b> Excitation spectrum for 1067 nm emission in blue region
Inset shows photographs of the samples in day light c> Ba1.94Eu0.06SiO4 and d>
Ba1.88Eu0.06Nd0.06SiO4, and under UV illumination e> Ba1.94Eu0.06SiO4 and f>
Ba1.88Eu0.06Nd0.06SiO4
Figure 7 : Luminescence decay curves for a> Ba1.94Eu0.06SiO4 and b> Ba1.88Eu0.06Nd0.06SiO4
379 nm excitation was used.
Figure 8: Mechanism of energy transfer from Eu2+ to Nd3+ involving emission of one photon
Figure 9: Mechanism of energy transfer from Eu2+ to Nd3+ involving emission of two photons
Figure 10 : Modification of Solar Spectrum using Ba2SiO4:Eu2+, Nd3+ phosphor.
a> AM1.5 solar spectrum, b> spectral response of c-Si solar cell, c> Nd3+ excitation spectrum
and d> Nd3+ emission spectrum
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Shaded portion shows the portion of solar spectrum adequate for quantum cutting.
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HIGHLIGHTS
ꢀ NIR emission at 1067 nm is reported for the first time in Ba2SiO4:Eu2+,Nd3+
ꢀ Excitation by near ultraviolet (nUV)/violet light.
ꢀ Energy transfer efficiencies for Eu2+ꢁ Nd3+ energy transfer close to 80 %.
ꢀ Attractive for application in photovoltaics based on c-Si