Synthesis of a Broad-Band Excited and Multicolor Tunable Phosphor

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Synthesis of a broadband excited and multicolor tunable phosphor Gd2SiO5: Ce3+, Tb3+, Eu3+ for NUV LED Xinguo Zhang, Yibo Chen, Liya Zhou, qi Pang, and Menglian Gong Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie404312n • Publication Date (Web): 01 Apr 2014 Downloaded from http://pubs.acs.org on April 7, 2014

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Industrial & Engineering Chemistry Research

Synthesis of a broadband excited and multicolor tunable phosphor Gd2SiO5: Ce3+, Tb3+, Eu3+ for NUV LED

Xinguo Zhang a,c,*, Yibo Chen b, Liya Zhou a, Qi Pang a, Menglian Gong c a

School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China b School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006,China c School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China.

* Corresponding author. Tel/Fax: +86-0771-3233718. E-mail address: [email protected]

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Abstract Broadband NUV-excited and multicolor-emitting Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors were synthesized by solid-state reaction. And the emission color of the phosphors can be tuned from blue (0.153, 0.091) to green (0.325, 0.495) and eventually to red (0595, 0.370) through efficient Ce3+→(Tb3+)n→Eu3+ energy transfer. NUV light was strongly absorbed by the Ce3+ ions, and the excited energy was transferred to Tb3+ ions, which produced intense green emission peaks. Finally, the excited energy was transferred from Tb3+ to Eu3+ ions, which is attributed to red emission peaks. These multicolor tunable Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors are promising materials for applications in NUV LEDs. Keywords: Phosphor; Energy transfer; Ce3+→Tb3+→Eu3+

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1. Introduction In the last few years, near-UV (NUV) LED based phosphor-converted white LEDs (pc-WLED) have attracted great attention 1. Ideally, phosphors for NUV LEDs must exhibit a strong absorption of NUV radiation and good stability. Eu3+ is an efficient ion for red phosphor with perfect color purity of 5D0→7F2 (λem = 615 nm) 2. However, Eu3+-activated phosphors have narrow line-shaped excitation peaks at NUV region 3,4, which are not desirable for NUV LED application. To broaden the excitation band and improve the absorption efficiency, co-doped other rare-earth ions with Eu3+ is a useful method. Recently, Eu2+/Ce3+-Tb3+ has been used to sensitize Eu3+ and realize the narrow-line red emission with near-UV broad band excitation, such as Ba2Tb(BO3)2Cl: Eu2+, Eu3+ 5 and Na2Y2B2O7: Ce3+, Tb3+, Eu3+ 6. However, borate host have some drawbacks like relative high phonon energy and low thermal stability. Silicates are suitable phosphor host with high physical/chemical stability and low phonon energy 7. Oxyorthosilicates Me2SiO5 (MSO) where Me = Y, Gd, Lu, doped with rare earth ions arouse a great interest due to their unique thermal and optical properties 8. The Ce3+-doped MSO hosts are reported as very attractive scintillators especially for medical and nuclear physics applications 9. The luminescent properties and quantum cutting of Gd2SiO5: Eu3+ under VUV-UV excitation has been reported by Chen et al 10,11. To the best of our knowledge, there is no paper about energy transfer and luminescent property of Ce3+, Tb3+, Eu3+ tri-doped Gd2SiO5. In this study, we report broadband excited, multicolor tunable emission from Gd2SiO5: Ce3+, Tb3+, Eu3+ system. Ce3+ was used as the sensitizer because the 4f-5d transition is a spin- and parity-allowed transition and Ce3+ has a high absorption cross-section. Because of energy transfer from Ce3+ to Tb3+ and Eu3+ ions, intense visible light is emitted under a single excitation wavelength and the emission color is continuously tuned by adjustment of the ratio of Ce3+/Tb3+/Eu3+. These broadband excited, multicolor tunable Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors are promising materials for applications in NUV LEDs. 2. Experimental Gd2(1-x-y)SiO5: xCe3+, yTb3+ (x = 0.005, y = 0~0.50) and Gd2(1-x-y-z)SiO5: xCe3+, yTb3+, zEu3+ (x = 0.005, y = 0.50, z = 0.003~0.04) samples were synthesized by solid-state method. The stoichionmetric amounts of raw materials Gd2O3 (99.99 %), SiO2 (A. R.), CeO2 (99.99 %), Tb4O7 (99.99%) and Eu2O3 (99.99%) were thoroughly mixed by grinding. They were sintered in a reducing atmosphere (N2: H2 = 90: 10) at 1500 ℃ for 6 h, 2 wt % BaF2 were added as flux. The amount of Ce3+ is fixed as 0.005 according to Ref. 12. For Ce3+, Tb3+, Eu3+ tri-doped sample, Tb3+ content is set as 0.50 referring to the optimization work in Ref. 6. X-ray powder diffraction (XRD) patterns of the products were recorded on a Rigaku D/max-IIIA diffractometer with Cu Kα radiation (λ = 1.5403 Å). The photo-luminescent excitation/emission (PLE/PL) spectra and decay times were measured by a EDINBURGH FLS920 spectro-photometer using Xe (450 W) lamp as excitation source.

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3. Results and discussion 3.1 Structural Characterization of the Products The XRD patterns of Gd2SiO5: 0.005Ce3+ and representative Gd2SiO5: 0.005Ce3+, 0.15Tb3+, Gd2SiO5: 0.005Ce3+, 0.50Tb3+ and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, 0.005Eu3+ phosphors are shown in Fig.1a. It is observed that the positions and relative intensities of the main diffraction peaks for all the samples are consistent with the Joint Committee on Powder Diffraction Standards card data (JCPDS card no. 40-0287) of Gd2SiO5. Gd2SiO5 crystallizes as a monoclinic structure with a space group of P21/c14 and lattice constants of a = 9.132 Å, b = 7.063 Å, c = 6.749 Å, V = 415.0 Å3. According to the crystal structure (Fig.1b), there are two cationic sites statistically occupied by Gd3+ ions. Gd(1) is nine-fold coordinated to oxygen, forming a tricapped trigonal prism. The Gd(2)O7 coordination polyhedron is a distorted capped octahedron. The ionic radii for Gd3+, Ce3+, Tb3+ and Eu3+ are 0.94, 1.01, 0.92 and 0.95 Å, respectively. Thus, due to the similar ionic radius and valence, the RE ion dopants (Ce3+/Tb3+/Eu3+) were expected to replace Gd3+ sites. Since there is slight difference between the radius of dopant ions and Gd3+ i.e. rCe3+ (1.01 Å) > rEu3+ (0.95 Å) > rGd3+ (0.94 Å) > rTb3+ (0.92 Å), the lattice volume is expected to expand for Ce3+/Eu3+-doped and shrink for Tb3+-doped. According to Bragg’s law (2d*sinθ= nλ), where n is an integer, λ is the wavelength of X-ray, d is the spacing between the planes in the atomic lattice, and θ is the angle between the incident ray and the scattering planes. Shrinkage of the lattice volume (d) will lead to the increase the 2-theta value (θ). As shown in Fig.1a, the 2-theta value of (021) peak is 28.82 o for Gd2SiO5 host. When Gd3+ (0.94 Å) is replaced by larger Ce3+ ion (1.01 Å), the volume expands and 2-theta value reduces to 28.73 o (Gd2SiO5: 0.005Ce3+). The 2-theta value increases to 29.09 o (y = 0.15) and further to 29.22 o (y = 0.50) for Gd2SiO5: 0.005Ce3+, yTb3+, since the volume shrinks with increasing smaller Tb3+ ion (0.92 Å) doping. As doped with slightly larger Eu3+ (0.95 Å), 2-theta value of (021) peak again reduces to 29.02 o (Gd2SiO5: 0.005Ce3+, 0.50Tb3+, 0.005Eu3+). The variation of 2-theta value in XRD patterns with different dopant ions confirm that RE ion dopants (Ce3+/Tb3+/Eu3+) are occupying Gd3+ sites in Gd2SiO5 host. There are two kinds of cation sites in Gd2SiO5 host: 9-coordinated Gd(1) site and 7-coordinated Gd(2). Both of their valances are +3. According to Hume-Rothery rules, dopant ion should have similar ionic radius (differ by no more than 15 %) and the same valance for a good doping. Since there is no cation with +2 or +4 valence available in Gd2SiO5 host, all dopant ions (Ce3+, Tb3+ and Eu3+) are expected to be +3 valences. No further charge compensation is needed since the charge of dopant ions (Ce3+, Tb3+, Eu3+) and replaced ions (Gd3+) is +3. Besides, the valence of europium ion could be identified by observing the profile of emission spectrum: A broad emission band is expected for Eu2+, which is characteristic for parity allowed 4f65d→4f7(8S7/2) transition of Eu2+ ions; A number of sharp emission peaks in the range of 580-650 nm (red region) are Eu3+ characteristic f-f forbidden transitions. Since there is red linear-emitting peak and no broadband observed in the emission spectra of Eu-doped samples (Fig.2 and Fig.3), it is confirmed that the europium ions in Gd2SiO5 host remain +3 valence and do not reduced to +2 even in reducing atmosphere.

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The line shape of Eu3+ emission seldom changes because most of the valence electrons of trivalent rare-earth elements are shielded by 5s and 5p outer electrons, and the f-f transitions of trivalent lanthanides are weakly affected by ligand ions in the crystals. However, a few transitions of the trivalent lanthanides are sensitive to the environment of the crystal, and these have been called hypersensitive transitions. According to the Judd-Ofelt theory, the electric dipole transition 5 D0→7F2 is hypersensitive, and the emission intensity is strongly influenced by ligand ions in the crystals. If Eu3+ occupies an inversion symmetry site, a dominant reddish orange emission will be obtained according to the magnetic transition 5D0→7F1. Conversely, an electric dipole transition 5 D0→7F2 will predominate in the emission spectra 13.Since Eu3+ ions occupy the Gd(1) and Gd(2) sites with no inversion symmetry (see Fig.1b), a red emission (5D0→7F2) whose intensity is stronger than that of orange emission (5D0→7F1) is expected in Eu3+-doped Gd2SiO5. 3.2 Photoluminescent Properties Fig.2a shows PL and PLE spectra of Gd2SiO5: 0.005Ce3+. The excitation spectrum of Gd2SiO5: Ce3+ monitored at 440 nm shows two excitation bands centered at 280 and 345 nm. The intense broad band at 300-420 nm suggests that this phosphor can be effectively excited by NUV LED chip. When excited at 345 nm, the emission spectrum of Gd2SiO5: Ce3+ shows a blue broadband emission peak at 440 nm due to d-f allowed transition. Fig.2b illustrates PL and PLE spectra of Gd2SiO5: 0.005Ce3+, 0.15Tb3+. The PLE spectrum consists of several bands at 260 nm (Tb3+ f-d transition), 345 nm (Ce3+ f-d transition) and 380 nm (Tb3+ f-f transition), whose profile is similar with Gd2SiO5: Ce3+. Excited at 345 nm, the Ce3+, Tb3+ co-doped phosphor emits weak blue light of Ce3+, and strong green light with main peaks at 488, 545, 586, 623 nm, which are ascribed to 5 D4→7FJ (J = 6, 5, 4, 3). As seen in Fig.2c, PLE spectrum of Gd2SiO5: Ce3+, Tb3+, Eu3+ monitoring Eu3+ emission has similar profile with the PLE band of Gd2SiO5: Ce3+, which indicates that efficient energy transfer from Ce3+ →Tb3+ →Eu3+ happens in the Ce3+, Tb3+, Eu3+ tri-doped sample. Under 345 nm excitation, Eu3+ ions emit intense red light with main peaks at 591, 614, 620 nm, which are assigned to 5D0→7FJ (J = 1, 2) transition. The orange emission peaks at 579 and 591 nm is assigned to 5D0→7F0 and 5D0→7F1 transition, while the dominant red emission peak at 613 nm is due to the 5D0→7F2 transition. The results indicated that the local symmetry of Eu3+ site belongs to non-inversion centrosymmetry in Gd2SiO5 host. PL spectra of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0.003~0.04) under 345 nm excitation are shown in Fig.3. For Gd2SiO5: 0.005Ce3+, yTb3+, characteristic blue emission of Ce3+ and green emission peaks of Tb3+ are observed due to Ce3+→ Tb3+ energy transfer. When Ce3+ concentration is fixed, the intensity of Ce3+ emission decreases monotonously with the increasing Tb3+ content, while the intensity of Tb3+ emission improves rapidly, reaches a maximum at y = 0.15, and remarkably decreases due to concentration quenching. With rising Tb3+ concentration, the distance between Tb3+ ions becomes closer and the energy migration to a second Tb3+ becomes higher, thus, concentration quenching of Tb3+ occurs. Heavily-doped Tb3+ will form a terbium chain in the form of Ce3+-(Tb3+)n-Eu3+, which could sensitize Eu3+ ions and realized the narrow-line red emission with near-UV broad band excitation

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. According to the optimization work of J. Shi et al 6, optimal Tb3+ content of Ce3+→(Tb3+)n→ Eu3+ is found to be in the range of y = 0.40-0.60, which can sensitize Eu3+ emission and block metal-metal charge transfer (MMCT) process between Ce3+ and Eu3+ (Ce3+ + Eu3+ → Ce4+ + Eu2+) 14. Thus, the Tb3+ content in Gd2SiO5: Ce3+, Tb3+, Eu3+ system is set to be y = 0.50. For Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+, when co-doped with Eu3+, Tb3+ emission decreases continuously, and the emission of Eu3+ at 591 nm and 614 nm increases until z > 0.005. Ce3+ sensitization is efficient for producing strong red emission, since the 4f→5d band transition is a spin- and parity-allowed transition. These results suggest that color tuning using the energy transfer of Ce3+-(Tb3+)n-Eu3+ energy transfer is much more efficient than Tb3+→Eu3+ doubly doped phosphor system. 3.3 Decay curves and Energy Transfer Tunable color emission from Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors due to energy transfer from Ce3+ to Tb3+, and from Tb3+ to Eu3+ was confirmed by measuring the decay times for Ce3+ emission as a function of Tb3+ content, and Tb3+ emission as a function of Eu3+ content, respectively. Both Ce3+ →Tb3+ and Tb3+ →Eu3+ energy transfer are attributed to multipolar interaction between donor and acceptor ions. The energy transfer probability via multipolar interaction can be described by following equation 15:

P( R) ∝

QA Rbτ D

∫

f D ( E ) FA ( E ) dE Ec

where P is the energy transfer probability, τD is the decay time of donor emission, QA is the total absorption cross-section of acceptor, R is the distance between donor and acceptor, b and c are parameters depending on the type of energy transfer. According to eqn (1), the energy transfer probability P is inversely proportional to decay time τD. Fig.4 shows Ce3+ and Tb3+ decay curves of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0.003~0.04), respectively. Both Ce3+ and Tb3+ lifetime decay curves have been analyzed by curve fitting and the decay curve can be fitted successfully by a second-order exponential function as the following equation:

I = A1 exp(−t / τ 1 ) + A2 exp(−t / τ 2 ) where I represents the luminescent intensity; A1 and A2 are constants; t is time; τ1 and τ2 are the decay times for the exponential components, respectively. Thus, the average decay time (τ*) can be determined using the following equation:

τ

∗

∫ = ∫

∞ 0

tI (t ) dt

∞ 0

I (t )dt

The average lifetime of the Ce3+ ions is determined to be 22.68 ns, which is in good agreement with the reported lifetimes of the Ce3+ ions. The decay curve of the Ce3+ ions, a single exponential function or a second-order exponential function, relies on the number of sites in the host lattice. In our case, the second-order exponential function fits well with the decay curve, which is in accord with the practical local environment of two kinds of Gd3+ sites 9. Fig.4a demonstrate that the decay time of Ce3+ emission decreased from 22.68 ns to 7.16 ns, as Tb3+ content increased and Eu3+

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co-doped, which proves the occurrence of Ce3+-(Tb3+)n-Eu3+ energy transfer. Meanwhile, Tb3+ decay time shorten from 1.689 ms (y = 0.50, z = 0) to 0.864 ms (y = 0.50, z = 0.05) with rising Eu3+ contents (Fig.4b). Therefore, it is concluded that the red emission peaks from Eu3+ ions are attributed to the energy transfer from Tb3+ to Eu3+ due to the shortened decay time of Tb3+ emission with increasing Eu3+ ions. The CIE chromaticity coordinates for Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors are presented in Fig.5. The emitting color can be tuned from blue (0.153, 0.091) to green (0.325, 0.495) and eventually to red (0595, 0.370), by changing the ratio of Ce3+/Tb3+/Eu3+. The CIE coordinates of Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ remain constant when z is beyond 0.005, which is corresponding to the observed spectra profiles in Fig.3. Fig.6 illustrates the energy level model for ET process of Ce3+ →(Tb3+)n →Eu3+. Upon UV irradiation, electrons of Ce3+ shift to the 5d excited state. When some of these electrons return to the ground states (2F7/2 and 2F5/2), the phosphor emits blue light. Meanwhile, other excited electrons shift to the 5D4 excited state of Tb3+ ions as a result of non-radiative (NR) resonant energy transfer. Then the electrons move from the 5D4 excited state to the 7Fj ground state, and green light is obtained. With heavily-doped Tb3+, it forms an ET chain of Tb3+ to sensitize Eu3+ ions and to circumvent the MMCT effect between Ce3+ and Eu3+. Tb3+→Eu3+ energy transfer is greatly enhanced, and excited electrons shift to the 5D1 excited state of Eu3+ ions. Finally, the electrons relax to 5D0 and give out red emission due to 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions. 4. Conclusions A series of color-tunable phosphors from blue to red were successfully synthesized with Ce3+-(Tb3+)n-Eu3+ energy transfer in Gd2SiO5: Ce3+, Tb3+, Eu3+. The Ce3+→(Tb3+)n→Eu3+ energy transfer process has been investigated by the photoluminescence emission and excitation spectra, the decay curves, and the effect of Tb3+/ Eu3+ concentration. The enhanced red light of Eu3+ with sharp emission lines could be obtained by the broad band excitation peak at about 360 nm from the allowed 4f-5d absorption of Ce3+ ions. The results suggest that these multicolor tunable Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors are promising materials for potential NUV LEDs application. Acknowledgment：： This work was supported by the scientific research foundation of Guangxi University (Grant No. XBZ120573) and National Natural Science Foundation of China (No. 51102054 and 61264003). The corresponding author would like to thank Dr. Yibo Chen for the help of optimization of synthesis condition of Gd2SiO5: Ce3+, Tb3+, Eu3+, as well as Prof. Liya Zhou and Prof. Qi Pang for their helpful discussion of Ce3+/Tb3+/Eu3+occupied sites. The authors thank Prof. Menglian Gong and Prof. Jianxin Shi (Sun Yat-sen University, Guangzhou, China) for providing the PL/PLE and decay measurements

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References:

(1) Ye. S, Xiao. F, Pan. Y.X, Zhang, Q.Y, Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties, Mater. Sci. Eng. R. 2010, 71, 1. (2) Yu. R, Noh. B, Choi. B, Jeong. J, Kang. J, Yi. S, Jang. J, Synthesis and luminescence properties of a novel red-emitting phosphor Ba3La(PO4)3: Eu3+ for solid-state lighting, J. Alloy. Compds. 2013, 576, 236. (3) Zhang. N, Guo. C, Jing. H, Photoluminescence and cathode-luminescence of Eu3+-doped NaLnTiO4 (Ln = Gd and Y) phosphors, RSC Adv. 2013, 3, 7495. (4) Zhang. L, Han. P, Han. Y, Lu. Z, Yang. H, Wang. L, Zhang. Q, Structure evolution and tunable luminescence of (Sr0.98−mBamEu0.02)2Ca(Mo1−nWn)O6 phosphor with ultraviolet excitation for white LEDs, J. Alloy. Compds. 2013, 558 , 2295. (5) Xia. Z, Zhuang. J, Liao. L, Novel Red-Emitting Ba2Tb(BO3)2Cl: Eu Phosphor with Efficient Energy Transfer for Potential Application in White Light-Emitting Diodes, Inorg. Chem. 2012, 51, 7202. (6) Wen. D, Shi. J, A novel narrow-line red emitting Na2Y2B2O7: Ce3+, Tb3+, Eu3+ phosphor with high efficiency activated by terbium chain for near-UV white LEDs, Dalton Trans. 2013, 42, 16621. (7) Zhang. X, Zhang. J, Wang. R, Gong. M, Photo-Physical Behaviors of Efficient Green Phosphor Ba2MgSi2O7: Eu2+ and Its Application in Light-Emitting Diodes, J. Am. Ceram. Soc. 2010, 95, 1368. (8) Wang. Y, Guo. X, Endo. T, Murakami. Y, Ushirozawa. M, Identification of charge transfer (CT) transition in (Gd,Y)BO3: Eu phosphor under 100–300 nm, J. Solid. State. Chem. 2004, 177,

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2242. (9) Valais. I, Kandarakis. I, Nikolopoulos. D, Michail. C, David. S, Loudos. G, Cavoursas. D, Pananyiotakis. G, Luminescence Properties of (Lu,Y)2SiO5 Ce and Gd2SiO5 Ce Single Crystal Scintillators Under X-Ray Excitation for Use in Medical Imaging System, IEEE Trans. Nuclear. Sci. 2007, 54, 11. (10) Chen. Y, Liu. B, Shi. C, Kirm. M, True. M, Vielhauer. S, Zimmerer. G., Luminescent properties of Gd2SiO5 powder doped with Eu3+ under VUV–UV excitation, J. Phys.: Condens. Matter. 2005, 17, 1217. (12) Yokata. H, Yoshida. M, Ishibashi. H, Yano. T, Yamamoto. H, Kukkawa. S, Cathodoluminescence of Ce-doped Gd2SiO5 and Gd9.33(SiO4)6O2 phosphor under continuous electron irradiation, J. Alloy. Compds. 2011, 509, 800. (13) Zhu. G, Ci. Z, Shi. Y, Que. M, Wang. Q, Wang. Y, Synthesis, crystal structure and luminescence characteristics of a novel red phosphor Ca19Mg2(PO4)14: Eu3+ for light emitting diodes and field emission displays, J. Mater. Chem. C. 2013, 1, 5960. (14) Setlur. A, Sensitizing Eu3+ with Ce3+ and Tb3+ to Make Narrow-Line Red Phosphors for Light Emitting Diodes, Electrochem. Solid. State. Lett. 2012, 15, J25. (15) Dexter. D. L, A Theory of Sensitized Luminescence in Solids, J. Chem. Phys. 1953, 21, 836.

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Figure captions: Fig.1 XRD patterns of representative Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors and (b) crystal structure of Gd2SiO5 and the coordination geometry of Gd sites Fig.2 PLE and PL spectra of Gd2SiO5: 0.005Ce3+ (a), Gd2SiO5: 0.005Ce3+, 0.15Tb3+ (b), and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, 0.005Eu3+ (c) Fig.3 PL spectra of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0.003~0.04) under 345 nm excitation Fig.4 Decay curves of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50, a) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0~0.05, b) Fig.5 The CIE chromaticity coordinates for Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors (inset are representative samples under 365 nm UV lamp of 24 W) Fig.6. Energy level scheme of energy transfer process of Ce3+→(Tb3+)n→Eu3+ in Gd2SiO5: Ce3+, Tb3+, Eu3+

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Figure 1 XRD patterns of representative Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors and (b) crystal structure of Gd2SiO5 and the coordination geometry of Gd sites 33x16mm (600 x 600 DPI)



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Figure 2 PLE and PL spectra of Gd2SiO5: 0.005Ce3+ (a), Gd2SiO5: 0.005Ce3+, 0.15Tb3+ (b), and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, 0.005Eu3+ (c) 37x26mm (600 x 600 DPI)


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Figure 3 PL spectra of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0.003~0.04) under 345 nm excitation 37x26mm (600 x 600 DPI)



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Figure 4 Decay curves of Gd2SiO5: 0.005Ce3+, yTb3+ (y = 0~0.50, a) and Gd2SiO5: 0.005Ce3+, 0.50Tb3+, zEu3+ (z = 0~0.05, b) 62x93mm (600 x 600 DPI)


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Figure 5 The CIE chromaticity coordinates for Gd2SiO5: Ce3+, Tb3+, Eu3+ phosphors (inset are representative samples under 365 nm UV lamp of 24 W) 24x26mm (600 x 600 DPI)



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Fig.6. Energy level scheme of energy transfer process of Ce3+→(Tb3+)n→Eu3+ in Gd2SiO5: Ce3+, Tb3+, Eu3+ 67x73mm (600 x 600 DPI)


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Synthesis of a Broad-Band Excited and Multicolor Tunable Phosphor

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