Sensors and Actuators B 173 (2012) 234–238
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Luminescence studies of europium doped yttrium oxide nano phosphor J.R. Jayaramaiah a,b , B.N. Lakshminarasappa a,∗ , B.M. Nagabhushana c a
Department of Physics, Bangalore University, Bangalore 560 056, India Department of Physics, Government First Grade College, Nargund 582 207, India c Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560 054, India b
a r t i c l e
i n f o
Article history: Received 10 March 2012 Received in revised form 11 June 2012 Accepted 30 June 2012 Available online 21 July 2012 Keywords: Oxide Optical material Scanning electron microscopy Thermoluminescence
a b s t r a c t Luminescence exhibiting europium doped yttrium oxide (Y2 O3 :Eu3+ ) phosphor was prepared by solution combustion method, using disodium ethylene diamine tetra acetic acid (EDTA-Na2 ) as fuel at ∼350 ◦ C. Powder X-ray diffraction (PXRD) pattern of Y2 O3 :Eu3+ revealed the cubic crystalline phase. The morphology of the samples was studied by scanning electron microscopy (SEM) and was foamy, fluffy and porous in nature. Fourier transformed infrared spectroscopy (FTIR) revealed prominent absorption with peaks at 3415, 1435, 875 and 565 cm−1 . Optical absorption studies showed the energy gap of the synthesized samples to be 5.4–5.5 eV. The photoluminescence (PL) of Y2 O3 :Eu3+ exhibiting emission peak at 611 nm under the excitation of 254 nm. Thermoluminescence of ␥-irradiated Y2 O3 :Eu3+ showed two well resolved TL glows with peaks at 460 and 610 K and they were analyzed by glow curve shape method and the activation energies were found to be 0.421 eV and 1.016 eV respectively. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Nanoparticles have gained an immense interest, in anticipation that this unexplored range of material dimensions will yield size-dependent properties. The physical and chemical properties vary drastically with size, which clearly represents a fertile field for materials research [1–3]. Producing nano scale materials opens new opportunities in the creation of product with enhanced properties for applications such as electronics, optics, medicine and magnetism. Luminescent phosphors are among the current nanostructures of materials that can be incorporated into various applications, viz., the development of flat-panel displays depends critically on the design of bright and stable phosphors [4]. Nanocrystalline phosphors are suitable for high definition television (HDTV) where conventional bulk phosphor cannot be used [5]. The morphology and the particle size affect the emission intensity of phosphor [6–8]. In general, the luminous efficiency of phosphor reduces with decreasing particle size as long as the quantum size effect does not occur [9]. Y2 O3 :Eu3+ nanopowder was synthesized by solution combustion technique in which EDTA-Na2 was used as the chelating-fuel. This EDTA has several remarkable advantages in comparison with other fuels. Because of the greater ability of EDTA anions to chelate metal cations and form very stable and soluble complexes, all of the starting materials are mixed
∗ Corresponding author. Tel.: +91 9448116281; fax: +91 80 23219295. E-mail addresses: jaya
[email protected] (J.R. Jayaramaiah),
[email protected] (B.N. Lakshminarasappa). 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.06.092
at the molecular or atomic level in a solution, it is easy to control the composition and a high degree of homogeneity is achievable. Solution combustion is a wet-chemical method; it is an exothermic reaction and occurs with the evolution of heat and light. Such a high temperature leads to growth of nanocrystalline materials. In any solution combustion fuel and oxidizer are required. When the mixture of fuel and oxidizer is ignited, combustion takes place. For the synthesis of oxides, metal nitrates are used as oxidizer and hydrazine based compounds are employed as fuels [10,11]. Optically transparent yttrium oxide (Y2 O3 ) appears to be a perspective laser material, because its thermal conductivity is two and ten times higher than thermal conductivity of YAG and glass respectively [12]. Nanophosphor Y2 O3 crystallites have high luminescence efficiency in the orange-red, high purity, good chemical resistance and thermal stability. Therefore the Y2 O3 :Eu3+ powder is largely used in optical display technology, medical image and illumination [13]. In recent years, pure or doped Y2 O3 has attracted much attention due to its potential application in optoelectronics. This is mainly due to the qualities of this material such as its high refractive index (>1.9), large band gap (5.8 eV), physical and chemical stability. Refractive index and band gap are crucial parameters in optical wave guide device. The higher the value of refractive index, the more confined the optical transmission in the guide, thus leading to more efficient pumping and amplification. Therefore, the investigation of the effects of refractive index and band gap is very important [14]. Y2 O3 :Eu3+ phosphor exhibits red emissions and has excellent chemical stability. This phosphor is the only existing red phosphor used in three band-fluorescent lamps [15]. Y2 O3 :Eu3+ has attracted
J.R. Jayaramaiah et al. / Sensors and Actuators B 173 (2012) 234–238
2. Experimental
3+
(136)
(541)
(611)
(026)
(600)
(622)
(440) (433)
(125)
(134)
(332)
(422)
(411)
(211)
(420)
Y1.94 Eu0.06O3
(400)
(222)
Y2O3:Eu
Intensity (a u)
a great deal of interest for use as red phosphor in fluorescent lamps, high-resolution projection TVs, protection devices and low voltage displays such as cathode ray tube, plasma display panels and field emission displays [16,17]. Recent studies on different luminescent nanomaterials have showed a potential application in dosimetry of ionizing radiations for the measurements of high doses using the TL technique [18]. Yttrium oxide doped with trivalent rare earth ions is a well known material for display and lamp applications. And, such materials may be investigated for their potential application as TL dosimeters or scintillating detectors [19]. The TL behavior of ␥ irradiated Y2 O3 :Eu3+ has been investigated in the present work. The TL glow peak intensity with ␥-ray dose increases and reaches a maximum for a dose of 2.232 kGy and decreases with increasing ␥-dose. The present material may be useful for dosimetric applications up to a dose of 2.232 kGy. The energy gap of the synthesized Y2 O3 :Eu3+ is found to be ∼5.5 eV.
235
Y1.95 Eu0.05O3 Y1.96Eu0.04O3 Y1.97 Eu0.03O3 Y1.98 Eu0.02O3
Y1.99 Eu0.01O3
20
30
40
50
60
2θ (deg) Nanophosphor Y2 O3 :Eu3+ was prepared by solution combustion synthesis. Yttrium oxide (99.99%, SD Fine Chemicals Ltd.), europium oxide (99.99%), nitric acid and EDTA-Na2 were used as starting raw materials to prepare Y2 O3 :Eu3+ . Stoichiometric amounts of Y2 O3 and Eu2 O3 were converted into nitrate by dissolving in 1:1 nitric acid and excess nitric acid was removed by evaporation on a sand bath. The stoichiometric amount of EDTA-Na2 was dissolved in double distilled water, the solution was poured in to the crystalline dish containing yttrium nitrate doped with Eu, and the stoichiometric solution was stirred well to ensure homogeneity. The dish with solution was placed in a muffle furnace whose temperature was maintained at 1 (1.23) and sub linear at higher doses f(D) < 1 (0.4). Hence, this behavior of the sample is useful for dosimetric application [18]. The effective atomic number (Zeff ) has been defined as
[b]
3+ 2.232 kGy γ-rayed Y2O3:Eu
20
Eu0.01
Eu0.02 Eu0.03
15
Eu0.04 Eu0.05
610 K
Eu0.06
10
16 460 K
TL Intensity (a u)
TL Intensity (a u)
24
5
8
0 300
0 400
500
600
700
400
500
600
700
Temperature (K)
Temperature (K)
Fig. 6. (a) Thermoluminescence glow curves of combustion synthesized and 2.232 kGy ␥-rayed Y2 O3 :Eu3+ . (b) Deconvoluted glow curves.
[a]
Y2O3:Eu
3+
Y2O3:Eu
γ-rayed for 16
20
[b]
3+
0.837 kGy
TL Intensity (a u)
(ii)
2.232 kGy 2.790 kGy 3.350 kGy
12
8
(i)
4
0 450
500
550
i
16
610 K
1.675 kGy
12
600
650
Temperature (K)
8
1
2
3
4
4
γ-Dose (kGy)
Fig. 7. (a) TL glow curves of combustion synthesized Y2 O3 :Eu3+ for different ␥-ray doses and (b) variation of glow peak intensity with dose.
ai Zim
(2)
where ‘ai ’ is the fractional electron content of element ‘i’ with atomic number ‘Zi ’. The value of ‘m’ will typically range from 3 to 4, with 3.5 a reasonable value [28]. ‘Zeff ’ of Y2 O3 :Eu3+ compound has been calculated (Eu0.01 = 36.49, Eu0.02 = 36.84, Eu0.03 = 37.18, Eu0.04 = 37.52, Eu0.05 = 37.85 and Eu0.06 = 38.16). Each of the above TL glow curves was analyzed based on glow curve shape method [29]. A typical result for a glow curve ␥-rayed for 2.232 kGy is shown in Fig. 8. The order of kinetics of glow curves was calculated by measuring the symmetry (geometrical) factor g ∼ 0.504 [g = ı/ω, (ı/) = 1.016 for 460 K] and g ∼ 0.489 [g = ı/ω, (ı/) = 0.957 for 610 K]. The values of , ı and ω are calculated, where ‘’ is the low-temperature half width of the glow curve i.e. = Tm − T1 , ‘ı’ is the high-temperature half width of the glow curve i.e. ı = T2 − Tm and ‘ω’ is the full width of the glow peak at its half height i.e. ω = T2 − T1 . From the values of the geometrical factor it is clear that the two glow peaks obey the general order kinetics. The trap depth also known as the activation energy of the luminescence centers is calculated using Chen’s equation [30].
0.558 kGy
Glow Peak Intensity (a u)
20
Zeff =
m
E˛ = C˛
2 kB Tm ˛
− b˛ (2Tm ),
(3)
where ‘kB ’ is Boltzmann constant, ‘Tm is peak temperature. The constants ‘C˛ ’ and ‘b˛ ’ were also calculated by the Chen’s equation. The mean activation energies and the frequency factors were found to be ∼0.421 eV, ∼40.58 × 103 Hz at 460 K and ∼1.016 eV, ∼0.243 × 109 Hz at 610 K. 4. Conclusions Y2 O3 :Eu3+ nanoparticles have been synthesized by the EDTANa2 assisted combustion technique at low temperature and in a very short time. PXRD pattern of these samples confirms the cubic phase. The crystallite size and the particle density were found to be 15–30 nm and ∼4.995 g cm−3 respectively. The SEM pictures of Y2 O3 :Eu3+ indicated the spatial structure of the loosely agglomerated particles which were fluffy, crispy with pores and voids in
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nature. The energy gap of Y2 O3 :Eu3+ was found to be 5.4–5.5 eV. PL emission peak centered at ∼611 nm is due to 5 D0 → 7 F2 transition of Eu3+ ions. TL glow curves were analyzed and the trap depths for the two luminescence centers corresponding to 460 K and 610 K glow peaks were calculated. Further, the ␥-irradiated Y2 O3 :Eu3+ shows good TL response up to the ␥-irradiation dose of 2.232 kGy. Hence, this phosphor may find use in radiation dosimetry. Acknowledgment The authors are thankful to ISRO-ISEC, advanced devices and radiation cell, Bangalore, for providing facilities for ␥-irradiation. References [1] G. Schmid, Clusters and Colloids from Theory to Applications, VCH, Weinheim, 1998. [2] A. Alivisators, Endeavour 21 (2) (1997) 57. [3] R. Andres, R. Averback, W. Brown, L. Brus, Journal of Materials Research 4 (1989) 704. [4] J. Mckittrick, L.E. Shea, C.F. Bacakski, E.J. Bosze, Displays 19 (1999) 169. [5] T. Igarashi, M. Ihara, T. Kusunoki, K. Ohno, T. Isobe, M. Senna, Applied Physics Letters 76 (2000) 1549. [6] W. Lenggoro, B. Xia, H. Mizushima, K. Okuyama, N. Kijima, Materials Letters 50 (2001) 92. [7] X. Jing, T. Ireland, C. Gibbons, D.J. Barber, J. Silver, A. Vecht, G. Fern, P. Trowga, Journal of the Electrochemical Society 146 (1999) 4654. [8] Y.C. Kang, S.B. Park, I.W. Lenggoro, K. Okuyama, Journal of Physics and Chemistry of Solids 60 (1999) 379. [9] K.K. Lee, Y.C. Kang, K.Y. Jung, H.D. Park, Electrochemical and Solid-State Letters 5 (2002) 31. [10] J.J. Kingsley, K.C. Patil, Materials Letters 6 (1988) 427. [11] K.C. Patil, S.T. Aruna, S. Ekambaram, Current Opinion in Solid State and Materials Science 2 (1997) 158. [12] A.A. Kaminskii, Laser crystals, Science (Moscow) (1975) 256. [13] N. Rakov, B. Whualkuer Lozano, G.S. Maciel, C.B. de Araujo, Chemical Physics Letters 428 (2006) 134. [14] L. Lou, W. Zhang, A. Brioude, C. Le Luyer, J. Mugnier, Optic Materials 18 (2001) 331. [15] Y. Tao, G. Zhao, W. Zhang, S. Xia, Materials Research Bulletin 32 (1997) 501. [16] J.Y. Zhang, Z.L. Tang, Materials Science and Engineering A 334 (2002) 246. [17] O.A. Serra, S.A. Cicillini, R.R. Ishiki, Journal of Alloys and Compounds 303–304 (2000) 316. [18] N. Salah, S.S. Habib, Z.H. Khan, S. Al-Hamedi, S.P. Lochab, Journal of Luminescence 129 (2009) 192. [19] P.J.R. Montes, M.E.G. Valerio, M.A. Macedo, F. Cunhaa, J.M. Sasaki, Microelectronics Journal 34 (2003) 557. [20] H.P. Klug, L.E. Alexander, X-ray Diffraction Procedures, 2nd ed., John Wiley and Sons, New York, 1974.
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Biographies J.R. Jayaramaiah completed his M.Sc. in nuclear physics during 1992 and M.Phil. in thin film during 1998 at Bangalore University (Bangalore, India). He is currently pursuing Ph.D. in luminescence at Bangalore University. He worked as a lecturer of physics at Vivekananda Degree College (Bangalore, India) from 1992 to 2005 and as a senior lecturer of physics (2006–2009) at Global Academy of Technology Bangalore. He is working as an assistant professor of physics at Government First Grade College (Hangal and Nargund, Karnataka, India) since 2009. B.N. Lakshminarasappa pursued his M.Sc. in solid-state-physics during 1976 at Sri Venkateswara University (India) and Ph.D. in physics (Color centers studies in sodium bromide single crystals) during 1990 at Bangalore University (Bangalore, India). He worked as a research assistant from 12.07.1982 to 20.03.1994 and as a lecturer from 21.03.1994 to 20.03.1998 at Bangalore University (Bangalore, India). He also worked as a senior lecturer from 21.03.1998 to 20.03.2003 at Bangalore University (Bangalore, India). He is working as a reader at Bangalore University (Bangalore, India) since 21.03.2003. His research area includes thermoluminescence and photo-luminescence studies in swift heavy ion irradiated nanocrystalline aluminum oxide, thermoluminescence studies in pure and La, Gd, and Cr doped dicalcium silicate nanophase systems, thermo stimulated luminescence studies in aluminum silicate polymorphs, color centers and thermoluminescence studies in some inorganic materials, growth, characterization, optical and electrical properties of semi conducting thin films, defect studies in some nanophase inorganic samples and spectroscopic studies of combustion synthesized swift heavy ion irradiated forsterite. B.M. Nagabhushana pursued his M.Sc. in physical chemistry during 1986 at Gulbarga University (India) and Ph.D. in Chemistry at Bangalore University (India) during 2008. He worked as a lecturer in chemistry 1986 to 1999, sr. Lecturer 1999 to 2004, as assistant professor 2004 to 2008 and now professor 2008 to till date at M.S.R.I.T Bangalore. The research area is mainly related to nano-materials: preparation, characterization and their studies on various properties like-optical, magnetic, catalytic, adsorption, antibacterial and luminescence. The preparation of nano materials is carried out via wet chemical methods like combustion, sol-gel, hydrothermal etc.
