Enhanced photoluminescence due to Bi3+ → Eu3+ energy transfer and re-precipitation of RE doped homogeneous sized Y2O3 nanophosphors

Accepted Manuscript Title: Enhanced Photoluminescence due to Bi3+ null Eu3+ Energy Transfer and Re-precipitation of RE doped homogeneous sized Y2 O3 nanophosphors Author: Abhijit P. Jadhav Sovann Khan Seung Yong Lee Jong-Ku Park Sung Wook Park Ju Hyun Oh Byung Kee Moon Kiwan Jang Soung Soo Yi Jung Hwan Kim So-Hye. Cho Jung Hyun Jeong PII: DOI: Reference:

S0025-5408(16)30263-X http://dx.doi.org/doi:10.1016/j.materresbull.2016.06.016 MRB 8816

To appear in:

MRB

Received date: Revised date: Accepted date:

19-4-2016 30-5-2016 8-6-2016

Please cite this article as: Abhijit P.Jadhav, Sovann Khan, Seung Yong Lee, Jong-Ku Park, Sung Wook Park, Ju Hyun Oh, Byung Kee Moon, Kiwan Jang, Soung Soo Yi, Jung Hwan Kim, So-Hye.Cho, Jung Hyun Jeong, Enhanced Photoluminescence due to Bi3+ srarr; Eu3+ Energy Transfer and Re-precipitation of RE doped homogeneous sized Y2O3 nanophosphors, Materials Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2016.06.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Enhanced Photoluminescence due to Bi3+ → Eu3+ Energy Transfer and Re-precipitation of RE doped homogeneous sized Y2O3 nanophosphors

Abhijit P. Jadhav,a,b Sovann Khan,a Seung Yong Lee,a Jong-Ku Park,a Sung Wook Park,c Ju Hyun Oh,c Byung Kee Moon,c Kiwan Jang,a Soung Soo Yi,d Jung Hwan Kim,e So-Hye. Cho,a*, Jung Hyun Jeongc**

a

Center for Materials Architecturing, Korea Institute of Science and Technology, Seoul, Republic of Korea, 027 92 b c

Department of Physics, Pukyong National University, Busan, Republic of Korea, 485 13.

d e

Department of Physics, Changwon National University, Changwon, Republic of Korea, 511 40.

Department of Materials Science and Engineering, Silla University, Busan, Republic of Korea 46958.

Department of Physics, Dongeui University, Busan, Republic of Korea, 473 40.

Email: [email protected], [email protected]

Graphical abstract

Highlights:   

Successful re-precipitation of supernatant solution to obtain phase pure nanophosphors. Fine tuning emission wavelength by adding dopant during re-precipitation reaction. Efficient luminescence enhancement with Bi3+ → Eu3+ energy transfer.

Abstract: Precipitation and re-precipitation of metal ions has been carried out from original and supernatant solution producing Bi3+ - Eu3+ doped Y2O3:Eu3+ and Eu3+ / Tb3+ doped Y2O3, respectively. Shorter reaction time is unable to consume all metal ions present in the solution which can be utilized through re-precipitation process. The doping of Bi3+ – Eu3+ in Y2O3 helps to absorb maximum UV light. The activation of Y2O3 matrix by Bi3+ and Eu3+ ions, together and separately, were studied considering the excitation energy transfer to the luminescence centers. The successful replacement of Y3+ by RE3+ ions can help for fine tuning of emission wavelength. Re-precipitation of supernatant solution by adding terbium precursor can successively produce uniform sized Tb3+ doped Y2O3:Eu3+. The re-precipitation of the supernatant solution ensure maximum consumption of metal ions for higher product yield and possible fine tuning of emission wavelengths. Keywords: Optical materials; chemical synthesis; phosphors; luminescence; nanostructures.

1. Introduction The research work on white light emitting diodes (LEDs) or so called fourth generation solid state light received considerable attraction in recent years. Their excellent properties such as small volume, long lifetime, high energy efficiency, energy saving and environment friendliness make them suitable candidate for display applications.[1–5] The theoretical concept put forward by Keodam and Postelten[6] fluorescent lamps with very high color rendering efficiency could be

achieved by the combination of red, green and blue phosphors which emit in narrow wavelength intervals centered on 450, 545 and 610 nm, respectively. These tricolor lamps have color rendering index (CRI) values of 80 – 85 at high efficiencies of 100 lm/W. Europium doped yttrium oxide is a top ranking red phosphor with high quantum efficiency of nearly 100% when excited by high energy UV radiation (254 nm). The strongest emission is located at 613 nm while other emission lines are weaker one.[7] The excitation wavelength for UV-LEDs lies in the region of 360 – 400 nm and Y2O3:Eu could be excited due to the 4f – 4f transition which was strongly forbidden by the parity selection rule. Yttrium oxide (Y2O3) is an important sesquioxides within the general class of ceramics which can find applications such as sintering aids in the various ceramic materials, substrates for semiconducting films, optical windows and most important component for rare earth doped lasers.[8] The selection of suitable host and dopants has been done by considering their crystal structure, ionic radii, emission efficiency, thermal conductivity, refractive index and phonon frequency.[9] Y2O3 shows wide band gap, low phonon frequency, wide transmission region and matching of ionic radii with many rare earth ions which make it favorable oxide host.[10] The incorporation of Bi3+ as a codopant into Y2O3:Eu3+ can be helpful for effective absorption of UV radiation in the range of 300 – 400 nm through its allowed 1S0 → 3P1 transition.[11,12] Bi3+ ion under UV region of the spectrum shows two strong absorption bands such as 1S0 → 3P1 and 1P1 [13] and Eu3+ ion shows a charge transfer absorption band in the same region where the position of the band depends strongly on the nature of the surrounding ions.[14] The transfer of electronic excitation between ions in the solids has been extensively studied for various applications. Along with intrinsic decay processes, excited donor ions have been found to relax by direct interaction

with energy transfer to acceptor ions or by migration of the excitation among donor ions until it comes into the vicinity of an energy acceptor where direct transfer occurs. In any case, observation of the time evolution of the donor luminescence under pulsed laser excitation provides help in identifying the dominant relaxation mechanisms.[15] In present paper, we have carried out synthesis of high emitting red emission phosphor from the original as well as first supernatant solution of urea precipitation reaction. While the emission wavelength was tuned by addition of terbium precursor to supernatant solution to obtain Tb co-doped Y2O3:Eu3+. To obtain small particle size in homogeneity the reaction time is an important factor to control the particle growth. During smaller reaction time in precipitation reaction, limited amount of metal ions got precipitated and some part of metal ions still remain in the solution. Usually the supernatant solution (obtained from removal of precipitated particles by centrifuge without any addition of DI water for washing) is discarded after the removal of precipitated particles and the valuable and sometime expensive metal ions are lost in trash. Thus to recover the metal ions which are still in the solution, the second urea precipitation reaction was carried out and the obtained product was high emission red and green-white phosphor. By this method we can certainly avoid the loss of expensive materials and maximize % yield of the product. 2. Experimental 2.1 Materials Yttrium (III) nitrate hexahydrate (Y(NO3)3•6H2O, 99.9%, Alfa Aesar – A John Matthey Company), europium (III) nitrate hexahydrate (Eu(NO3)3•6H2O, >99%, Alfa Aesar – A John Matthey Company), bismuth (III) nitrate pentahydrate (Bi(NO3)3•5H2O, 98%, Alfa Aesar – A John Matthey

Company), terbium nitrate hexahydrate (Tb(NO3)3•6H2O, 99.99%, Energy Chemicals), urea ((NH2)2CO, high purity, Sigma – Aldrich) were used as received without further purification. 2.2 Synthesis: The synthesis of Bi and Eu doped yttrium oxide was carried out by precipitation of basic solution by urea.[16] Powder samples of Bi and Eu codoped Y2O3 were prepared with the stoichiometric ratio of Y1.83Bi0.09Eu0.08O3. The precursors [yttrium nitrate hexahydrate – 0.0183 mmol and europium nitrate hexahydrate – 0.0008 mmol] were calculated for 250 mL solution. Except bismuth nitrate pentahydrate, other precursors were transferred to the round bottom flask and 249 mL solution was prepared using DI water and it was stirred at room temperature for about 2 hours using magnetic stirring. The temperature of the solution was increased to 80 oC. Bismuth precursor (bismuth nitrate pentahydrate – 0.0009 mmol) was added in minimum amount of water, e.g. 1mL of DI water and mixed with earlier reaction solution at around 70 oC and after reaching the temperature to 80 oC it was maintained for 10 minutes. A white colored precipitate was appeared in the solution indicating the hydrolysis of nitrate salts. After hydrolysis reaction, the solution pH changes from 4.0 to 6.2. After 10 minutes of reaction time, the temperature of the solution was quenched down to room temperature by keeping the reaction flasks in ice water bath. Once the temperature of the solution returns to normal the precipitate was separated using centrifuge at 10,000 rpm for 10 minutes at room temperature. The first supernatant solution was collected separately. For Tb co-doped Y2O3:Eu3+, terbium precursor (0.00092 mmol) was added prior to heating the solution and stir at room temperature for 1 hour. This supernatant solution was taken into separate round bottom flask and was heated at 80 oC for 10 minutes. The precipitate obtained from supernatant solution was collected and washed thoroughly using DI water for 2 – 3 times and finally it was washed using

ethanol to remove soluble impurities. The precipitates were dried in air oven at 120 oC for 4 – 5 hours and later it was calcinated at 800 oC for 2 h in air atmosphere. The obtained %yield from original solution and supernatant solution was around 62.22 and 30.60%, respectively. 2.3 Characterization The powder X-ray diffraction (XRD) patterns of the annealed samples were recorded using the Cu K radiation (λ= 1.54056 Å) on Bruker D8 advanced diffractometer operating at 40 kV and 40 mA at a scanning rate of 0.05° per step in the 2θ range of 10° ≤ 2θ ≤ 80°. The reference data for the comparison of obtained diffraction patterns were obtained from JCPDS cards. Particle size and morphology of the calcinated nanophosphors were detected by E-SEM (environmental SEM) (FEI – XL – 30 FEG with accelerating voltage < 30 kV). The room temperature photoluminescence properties of the quantum cutting phosphor is explored using Hitachi F – 7000 fluorescence spectrophotometer with a 200 W xenon lamp source and PTI (USA) operated by Xenon lamp light source. 3. Results and discussion 3.1 Structure and morphology Figure 1 shows scanning electron microscopy images of Bi3+ codoped Y2O3:Eu3+ synthesized by urea precipitation method with original and supernatant solution along with Tb doped Y2O3:Eu3+, respectively. The successful synthesis from original and supernatant solution produce uniform sized non-agglomerated nanostructures. The nanoparticles are spherical in shape and having uniform size distribution after calcination at 800 oC for 2 h. The sample prepared from urea precipitation of original solution shows uniform particle size around 55 nm. The particle size

increases to 120 – 150 nm during the secondary precipitation reaction. The reaction for original solution was quenched after 10 minute heating. The nucleation of the precipitated product occurred during that moment remain in the solution. During secondary urea precipitation, the growth of previously nucleated particles occurs which results in increase in particle size of supernatant reaction products. Although the particle size is uniform and similar in size the elemental composition varies highly in sample prepared from original and supernatant solution. Table 1 shows X-ray fluorescence spectroscopy data representing atomic % of each element (excluding oxygen) in heat treated Y2O3:Eu3+, Bi3+ synthesized using original and supernatant solutions along with and Tb3+ doped Y2O3:Eu3+ by urea precipitation method. The elemental analysis of original solution product shows 82.2 atom% of Y, 3.67 atom% of Eu and 14.13 atom% of Bi, respectively. In response to secondary reaction, the obtained product from supernatant solution shows elemental composition of 97.72 atom% of Y, 2.18 atom% of Eu and 0.11 atom% of Bi, respectively. While the product obtained from Tb3+ doped Y2O3:Eu3+ shows 80.42 atom% of Y, 4.98 atom% of Eu, 14.50 atom% of Tb and very small amount of Bi in 0.1 atom%. From the large difference in elemental composition observed in the calcined products prepared from primary and supernatant solution we can see the precipitation ability of individual element in the solution decides the composition of the final product. Unlike yttrium and europium nitrates, Bi(NO3)3•5H2O is insoluble in aqueous solution but radially decomposed to subnitrate form BiO(NO3).[17] Bismuth (III) nitrate pentahydrate is a compound which on hydrolysis with water produces basic salts and subnitrate such as Bi(OH)2NO3 [18] and Bi2O2(OH)NO3 [19, 20] The incorporation of bismuth precursor in the original reaction mixture was made at around 70 oC, when urea hydrolysis is about to take place. As explained by Kragten et al.[21] for the precipitation ability of bismuth oxy-nitrate changes with respect to change in solution pH. The initial pH of the

precursor solution (without Bi precursor) was around 4 and after hydrolysis of urea pH changes to 6. When bismuth precursor was added to reaction mixture immediate turbidity appears and once the solution reaches at 80 oC, precipitation of metal hydroxide carbonate complex starts. With change in solution pH, precipitation of solid BiONO3, Bi(OH)2+ and {Bi(OH)3}solid takes place depending on the amount of bismuth subnitrate formed after reaction of bismuth nitrate pentahydrate with DI water. Thus to understand the urea precipitation reaction we need to write the reaction mechanism separately for Y – Eu and Bi due to their different solubility in aqueous solvent. 𝐻2 𝑁 − 𝐶𝑂 − 𝑁𝐻2 ↔ 𝑁𝐻4+ + 𝑁𝐶𝑂−

(1)

𝑁𝐶𝑂− + 𝑂𝐻 − + 𝐻2 𝑂 → 𝐶𝑂32− + 𝑁𝐻3

(2)

[(𝑌1.83−𝑥 𝐸𝑢𝑥 )(𝐻2 𝑂)𝑛 ]3+ + 𝐻2 𝑂 ↔ [(𝑌1.83−𝑥 𝐸𝑢𝑥 )(𝑂𝐻)(𝐻2 𝑂)𝑛−1 ]2+ + 𝐻3 𝑂+

(3)

[(𝑌1.83−𝑥 𝐸𝑢𝑥 )(𝑂𝐻)(𝐻2 𝑂)𝑛−1 ]2+ + 𝐶𝑂32− → (𝑌1.83−𝑥 𝐸𝑢𝑥 )(𝑂𝐻)𝐶𝑂3 . 𝐻2 𝑂 + (𝑛 − 2)𝐻2 𝑂

(4)

In case of bismuth nitrate pentahydrate, the possible hydrolysis reaction can be written as, 𝐵𝑖(𝑁𝑂3 )3 . 5𝐻2 𝑂 + 𝐻2 𝑂 + 𝑁𝐻3 + 𝐶𝑂32− → 𝐵𝑖𝑂(𝑁𝑂3 )/ 𝐵𝑖(𝑂𝐻)2 𝑁𝑂3 / 𝐵𝑖2 𝑂2 (𝑂𝐻)𝑁𝑂3 (5) 𝐵𝑖𝑂(𝑁𝑂3 )/ 𝐵𝑖(𝑂𝐻)2 𝑁𝑂3 / 𝐵𝑖2 𝑂2 (𝑂𝐻)𝑁𝑂3 + 𝑁𝐻3 + 𝐻2 𝑂 → 𝐵𝑖(𝑂𝐻)+ 2 + {𝐵𝑖(𝑂𝐻)3 }𝑠𝑜𝑙𝑖𝑑 (6) It should be noted that, the aim of our experiment has no relation with intermediate phase identification related with bismuth subnitrate or bismuth hydroxide thus we have not carried out any kind of phase identifying characterization. Thus the reaction product written in equation 5 and 6 are possible products of the reaction.

The successful formation of crystalline Y2O3 has a cubic bixbyite structure with an Ia3 space group, [21, 22] has been confirmed by X-ray diffraction analysis. The figure represents comparison of XRD patterns of calcinated Y2O3 phosphors doped with Eu and Bi and Tb. All of the Bragg reflections in the diffraction patterns were indexed by comparing with standard diffraction peaks of the body centered cubic structure (space group Ia3) of Y2O3 (JCPDS # 83-0927). No additional secondary phase, impurities and any traces of amorphous nature were observed indicating structural purity of the calcinated products. The crystallite size calculated from Scherrer formula for the calcined product obtained from original solution and supernatant solution is 19.48, 26.63 and 25.48 nm, respectively. The intensity of main peak (222) was found increasing in the products of supernatant reactions and slightly shifting to higher  value. 3.2 Spectroscopic properties The photoluminescence properties of the calcined product of original solution has been shown in Figure 3. The sample was excited with emission wavelength em. = 613 nm and in response the excitation peaks due to electronic transitions of Eu and Bi at respective energy levels were observed. The broad excitation peak from 200 – 280 nm was obtained due to charge transfer mechanism between Eu3+ and O2– along with peaks at 416 and 465 nm representing electronic transition 7F0 → 5L6 and 7F0 →5D2, respectively.[23] The relative intensity of the excitation peaks around 465 nm is quite strong and exceeding the intensity of 254 nm peak. The observance of strong peak around 470 nm can be well coincide with the excitation wavelength demands of the blue LEDs (em = 440 – 470 nm) or the UV – LEDs (em = 370 – 410 nm).[24-26] The electronic transition in Bi3+ resulting from absorption of ground state electron from 1S0 → 3P1 level show

broad peak starting from 300 – 410 nm peaking at 341 nm. Considering the as obtained two excitation wavelengths the emission spectra was also measured using excitation wavelength due to charge transition of Eu and Bi, respectively. From the comparison of emission spectra, the relative intensity of the emission peak excited with 341 nm wavelength was almost 3.5 times stronger than the emission peak excited with 246 nm wavelength. It also indicate successful energy transfer happened between Bi3+ and Eu3+ ions and Bi3+ ions plays dual role of luminescence activator and a sensitizer for Eu3+ ions. From the reference of Table 1 we can see the amount of Bi in calcined product is nearly 4 times the amount of europium in Y2O3 host crystal, thus more energy is absorbed by bismuth and successively transferred to europium which results in stronger emission at 613 nm. The calcined product of supernatant reaction was emitted at 613 nm to find out various excitation wavelengths due to incorporation of bismuth and europium as shown in Figure 4. A strong excitation peak at 252 nm indicating effective charge transfer between Eu3+ – O2– following peak at 330 nm due to excitation of ground state Bi ions from the absorption of ground state electron from 1S0 → 3P1 level. The successive transfer of energy from Bi ions excites Eu ions to 5

L6 and 5D2 levels (7F0 → 5L6 and 7F0 →5D2) from ground state level 7F0, resulting into strong

excitation peaks at 394 and 465 nm. The big difference in the intensity of excitation peaks can be attributed to amount of respective dopants (Eu and Bi) in the calcined product (Table 1). The excited state ions from high energy level 5D0 returns to ground state 7F2 via electronic transitions 5

D0 – 7FJ, (J = 0, 1, 2, 3 and 4) representing a group of five sharp peak with most intense peak at

613 nm. Knowing the excitation wavelengths the sample was excited at 252, 330, 390 and 465 nm,

respectively. As shown in the Figure 4 inset, the emission wavelength at 613 nm shows maximum intensity at 252 nm excitation. The energy transfer mechanism between Bi3+ and Eu3+ in Bi – Eu doped Y2O3 has been schematically represented in Figure 5. Under UV radiation, Bi3+ ions absorb the excitation energy of 341 nm. The absorbed energy through 1S0 → 1P1 transition relaxes down to 3P1 energy level and transferred to Eu3+ ions through non radiative transitions. The energy transfer makes Eu3+ ions takes place 7F0,1 – 5L6, 7F0,1 – 5D2 transitions. Finally after reaching to 5D2 energy level, the excited Eu3+ ions emit red light around 613 nm through 5D0 → 7FJ (J = 0, 1, 2, 3 and 4) transitions.

Figure 6 shows photoluminescence excitation and emission spectrum of Tb3+ doped Y2O3:Eu3+ prepared from supernatant solution by urea precipitation method. The broad excitation peak in the UV region is composed of excitation due to Tb3+ ions with 7F6 → 4f – 5d and Eu3+ – O2- charge transfer phenomenon. Under the excitation of 303 nm wavelength, corresponding emission peaks of Tb3+ were observed at 544 nm through 5D4 – 7F5 transition. The peak at 611 nm is the result of overlapped 5D4 – 7F3 transition due to Tb3+ and 5D0 – 7F2 transition due to Eu3+, respectively. The spectral data shows successful formation of Tb3+ doped Y2O3:Eu3+ using supernatant solution of urea precipitation reaction. The CIE chromaticity coordinates of (A) Y2O3:Eu3+,Bi3+ (original sol.), (B) Y2O3:Eu3+ (supernatant sol.) and (C) Tb3+ doped Y2O3:Eu3+ based on their corresponding emission spectra has been shown in Figure 7. The CIE color coordinates of the sample (A), (B) and (C) are (0.5524, 0.3416), (0.6223, 0.0.3267) and (0.3378, 0.3630), respectively. The chromaticity coordinates of

sample (A), (B) and (C) shows the flexibility of tuning emission color from the successive precipitation reactions of original and supernatant solutions. 4. Conclusions The successful synthesis of red emitting Y2O3:Eu3+, Bi3+ and Y2O3:Eu3+ and white-green emitting Tb3+ doped Y2O3:Eu3+ has been carried out from the single reaction mixture. Urea precipitation reaction from supernatant solution insures higher product yield and maximum utilization of expensive rare earth precursors. It also produces uniform sized particles which is one of the important criteria for effective application of phosphor materials in various technologies. The difference in elemental composition and obtained stoichiometric ratio can be assigned to difference in solubility product value at reaction temperature. The incorporation of bismuth in Eu doped Y2O3 ensure absorption of maximum UV light which is a necessary requirement for its application in optoelectronic devices. The possible energy transfer between Bi3+ and Eu3+ has also been discussed for the product obtained from original solution and supernatant solution. The successful incorporation of Tb3+ into Y2O3 host crystal has been carried out from the urea precipitation reaction of supernatant solution which also ensures successful color tuning as well as avoid wastage of expensive metal precursors. Acknowledgements We thank the financial support from the Korea Institute of Science and Technology (KIST) institutional funding (Project No. 2E26120) and the international cooperation program managed by the National Research Foundation of Korea (NRF-2014K1A3A1A09063246). Tb3+ doped Y2O3:Eu3+ Nanostructures were supplied by the Display and Lighting Phosphor Bank at Pukyong National University.

Notes and references 1. J. S. Kim, P. E. Jeon, J. C. Choi, H. L. Park, S. I. Mho, G. C. Kim, Appl. Phys. Lett. 84 (2004) 2931. 2. Y. Hu, W. Zhuang, H. Ye, S. Zhang, Y. Fang, X. Huang, J. Lumin. 111 (2005) 139. 3. A. H. Mueller, M. A. Petruska, M. Achermann, D. J. Werder, E. A. Akhadov, D. D. Koleske, M. A. Hoffbauer, V. I. Klimov, Nanolett. 5 (2005) 1039. 4. N. Narendran, Y. Gu, J. P. Freyssinier – Nova, Y. Zhu, Phys. Status Solidi (a) 202 (2005) R60. 5. Y. Q. Li, A. C. Delsing, G. DeWith, H. Hintzen, Chem. Mater. 17 (2005) 3242. 6. M. Koedam, J. Postelten, Light Res. Technol. 3 (1971) 205. 7. G. Blasse, B. C. Grabmaier, Luminescent Materials, Springer-Verlag, New York (1994). 8. T.K. Anh, P. Benalloul, C. Barthou, L.T.K. Giang, N. Vu, L.Q. Minh, J. Nanomater. (2007) 1–10. 9. V. Singh, V. K. Rai, I. Ledoux-Rak, S. Watanabe, T. K. Gundu Rao, J. F. D. Chubaci, L. Badie, F. Pelle, S. Ivanova, J. Phys. D 42 (2009) 65104. 10. T. K. Anh, P. Benalloul, C. Barthou, L. T. K. Giang, N. Vu, L. Q. Minh, J. Nanomater. (2007) 1–10. 11. G. S. Ofelt, J. Chem. Phys. 37 (1962) 511. 12. B. Li, J. Lin, S. Sun, J. Inorg. Mater. 8 (1993) 207. 13. R. K. Datta, J. Electrochem. Soc. 114 (1967) 1137. 14. D. S. Mcclure, Electronic Spectra of Molecules and Ions in Crystals, Academic Press, New York, 1959.

15. C. K. Jorgensen, Mol. Phys. 5 (1962) 271. 16. L. S. Chi, R. S. Liu, B. J. Lee, J. Electrochem. Soc. 152-8 (2005) J93-J98. 17. B. Moine, J. C. Bourcet, G. Boulon, R. Reisfeld, Y. Kalisky, J. Physique 42 (1981) 499 – 503. 18. H. Suzuki, Y. Matano in Organobismuth Chemistry, Elsevier Science, First ed. Amsterdam, The Netherlands pg. 12. 19. G. Hägg, General and Inorganic Chemistry, John Wiley & Sons, Inc., New York, 1969, p. 580. 20. A. F. Holleman, E. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter & Co., Berlin, 1971, p. 440. 21. J. Kragten, L. G. Decnop – Weever, P. Grundler, Talanta 40 – 4 (1993) 485 – 490. 22. F. Hanic, Acta Crystallographica Section B-Structural Science, 40(Apr) (1984) 76 – 82. 23. Y. N Xu, Z. Q. Gu, W. Y. Ching, Phys. Rev. B, 56 – 23 (1997) 14993 – 15000. 24. R. Bazzi, M. A. Flores, C. Louis, K. Lebbou, W. Zhang, C. Dujardin, S. Roux, B. Mercier, G. Ledoux, E. Bernstein, P. Perriat, O. Tillement, J. Colloid. Interface. Sci. 273 (2004) 191. 25. X. Wu, Y. Liang, R. Liu, Y. Li, Mater. Res. Bull. 45 (2010) 594. 26. X. Wu, Y. Liang, R. Chen, M. Liu, Y. Li, J. Mater. Sci. 46 (2011) 5581 – 5586.

Figure and Captions: Figure 1: SEM images of Y2O3:Eu3+Bi3+ (original and supernatant solution) and Y2O3:Eu3+Tb3+ (supernatant solution) nanostructures. The samples were calcinated at 800 oC for 2 h in air atmosphere. Figure 2: X-ray diffraction patterns of Y2O3:Eu3+Bi3+ prepared from original solution and products obtained from supernatant solution. The samples were calcinated at 800 oC for 2 h in air atmosphere. Figure 3: Photoluminescence excitation and emission spectrum of Y2O3:Eu3+Bi3+ prepared from original solution by urea precipitation method. The sample was calcinated at 800 oC for 2 h in air atmosphere. Figure 4: Emission and UV light excitation response of Y2O3:Eu3+Bi3+ prepared from supernatant solution by urea precipitation method. The sample was calcinated at 800 oC for 2 h in air atmosphere. Figure 5: Energy level diagram indicating energy transfer process between Bi3+ - Eu3+ under UV excitation. Figure 6: Photoluminescence excitation and emission spectrum of Y2O3:Eu3+Tb3+ prepared from supernatant solution by urea precipitation method. The sample was calcinated at 800 oC for 2 h in air atmosphere. Figure 7: CIE color coordinates of (A) Y2O3:Eu3+, Bi3+ (original sol.), (B) Y2O3:Eu3+ (supernatant) and (C) Tb3+ doped Y2O3:Eu3+ (supernatant).

Figure 1

Intensity (a.u.)

JCPDS (83-0927) Original Supernatant Tb doping

10

Figure 2

20

30

40

50

2 (Degree)

60

70

80

120

emi. = 613 nm exc. = 246 nm exc. = 341 nm

D0  7F2

5 3+

Bi S0  3P1

80

1

60 Eu3+-O2charge transfer

F0  5D2

D0  7F4 5

D0  7F3 5

5

5

7

20

D0  7F0 5 D0  7F1

7

D1  7F1

40

F0 5L6

Intensity (a.u.)

100

0 200

300

400

500

Wavelength (nm) Figure 3

600

700

Eu3+-O2charge transfer

1000

1200 D0  F2 7

5

1000

500

0

200

500 400 300 Excitation wavelength (nm)

800 Eu3+ 7 F0  5D2

600

D0  7F4 5

D0  7F3

5

200

5

A  3A

1

5

400

D0  7F0 5 D0  7F1

Bi3+ in C2 site

D1  7F1

Intensity (a.u.)

Intensity (a.u.

1400

0 200

300

400

500

600

Wavelength (nm) Figure 4

700

800

Figure 5

5

700

F6  4f - 5d

5

200

500 400

5

D4  7 F 3

200

100

300

400

500

600

Wavelength (nm) Figure 6

300

700

100 800

Emission

D0  7 F 2

300

5

400

D4  7 F 4

500

0 200

700 600

D4  7 F 6

Excitation

600

Excitation Emission

5

7

D4  7 F 5

Figure 7

Table 1: X-ray fluorescence spectroscopy data representing atomic % of each element (excluding oxygen) in heat treated Y2O3:Eu3+, Bi3+ synthesized using original and supernatant solutions and Tb doped Y2O3:Eu3+ by urea precipitation method.

Component

Original sol. (atom %)

Supernatant (atom %)

Supernatant (Tb doping) (atom %)

Y

82.2

97.72

80.42

Eu

3.76

2.18

4.98

Bi

14.13

0.11

0.10

Tb

-

-

14.50