lable at ScienceDirect Journal of Alloys and Compounds 648 (2015) 467e473 Contents lists avai Journal of Alloys and Compounds journal homepage: http: / /www.elsevier .com/locate/ ja lcom Synthesis, characterization and evaluation of scintillation properties of Eu3þ-doped Gd2O3 obtained using PEG as precursor Lorena P.B. Durante a, Leonardo A. Rocha a, Daniela P. dos Santos a, Fernando O. Coelho a, Marco A. Schiavon a, Sidney Jos�e L. Ribeiro b, Jefferson L. Ferrari a, * a Laborat�orio de Materiais Inorgânicos Fotoluminescentes e Polímeros Biodegrad�aveis (LAFOP), Grupo de Pesquisa em Química de Materiais e (GPQM), Departamento de Ciências Naturais, Universidade Federal de S~ao Jo~ao Del Rei, Campus Dom Bosco, Praça Dom Helv�ecio, 74, 36301-160, S~ao Jo~ao Del Rei, MG, Brazil b Instituto de Química, UNESP, P.O. Box 355, 14800-970, Araraquara, SP, Brazil a r t i c l e i n f o Article history: Received 28 July 2014 Accepted 27 June 2015 Available online 2 July 2015 Keywords: Photoluminescence Scintillator Rare earth Polyethyleneglycol Gadolinium oxide * Corresponding author. Grupo de Pesquisa em Qu Universidade Federal de S~ao Jo~ao del Rei, Departa Campus Dom Bosco, Praça Dom Helv�ecio, 74 e F�abr Brazil. E-mail addresses: ferrari@ufsj.edu.br, jeffersonferr http://dx.doi.org/10.1016/j.jallcom.2015.06.239 0925-8388/© 2015 Elsevier B.V. All rights reserved. a b s t r a c t This work reports on the synthesis of Eu3þ-doped Gd2O3 using PEG as an organic molecular precursor with 1, 3, 5, 7 e 10 mol% of Eu3þ. TGA and DTA analysis of the precursors obtained shows that the final materials are obtained at thermal treatment above 700 �C. Based on this information all materials were obtained after heat treatment at 900, 1000 and 1100 �C during 4 h in an oven under air atmosphere. XRD analysis showed that the materials obtained after heat-treatment presents a cubic crystalline structure assigned to the Gd2O3. Crystallite size and microstrain were evaluated using the Scherrer's equation and Williansom-Hall method, respectively, as a function of heat-treated temperature and Eu3þ concentration. Raman spectroscopy also showed the formation of the Gd2O3 phase, however, the absence of bands around 117 cm�1 in the spectra with higher Eu3þ concentration indicates that the insertion of this one in the host matrix promotes the breakdown of some chemical bonds of the matrix. Intense photo- luminescence emission in the visible region with maximum localized around 611 nm under excitation at 255 nm with xenon lamp and with X-ray source were observed. The emissions observed were attributed to the intraconfigurational fef transitions of Eu3þ. The lifetime values of the 5D0 excited state were between 2.84 and 2.89 ms, indicating the location of Eu3þ in crystalline systems. This result demon- strates the potential application of the materials in systems for absorption in the ultraviolet region, solar cells, devices generated images and scintillation systems. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Current research on materials with great photoluminescent properties provides challenges for development of new technolo- gies in many areas, including electronics, photonics, imaging de- vices generators, optical amplification and detection, fluorescent detection in biomedical engineering and environmental control [1]. Among the materials that are promising for these applications, those that contain Rare Earth ions (RE3þ) in their compositions has special interest. Materials containing RE3þ have been studied and ímica de Materiais (GPQM), mento de Ciências Naturais, icas, S~ao Jo~ao Del Rei e MG, ari@gmail.com (J.L. Ferrari). excellent photoluminescent results have been obtained due to upconversion [2e4] and downconversion [5e7] properties. Depending on nature of the ions, the RE3þ present different intraconfigurational fef transitions and can generate emission or/ and absorption properties ranging from the X-ray, ultraviolet and visible to infrared region of the electromagnetic spectrum [8]. Among RE3þ, europium (Eu3þ) is a chemical element belonging to the class of lanthanide, found in oxidation states II and III, in which, the oxidation state III offers greater stability. The Eu3 þ have the electron configuration [Xe]-4F6. The bands present in the spectrum of emission of Eu3þ are very well known, and are derived from the transitions fef attributed to the energy levels 5D0/ 7FJ (in which J ¼ 0, 1, 2, 3, 4, etc) [8]. The most intense emission band in the spectrum is located in the region around 612 nm, red region of the electromagnetic spectrum attributed to the transition 5D0/ 7F2, known as a hypersensitive transition. This Delta:1_given name Delta:1_surname Delta:1_given name Delta:1_surname Delta:1_given name Delta:1_surname Delta:1_given name mailto:ferrari@ufsj.edu.br mailto:jeffersonferrari@gmail.com http://crossmark.crossref.org/dialog/?doi=10.1016/j.jallcom.2015.06.239&domain=pdf www.sciencedirect.com/science/journal/09258388 http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2015.06.239 http://dx.doi.org/10.1016/j.jallcom.2015.06.239 http://dx.doi.org/10.1016/j.jallcom.2015.06.239 Fig. 1. TGA/DTA analysis of precursors viscous solutions containing Eu3þ: A) 1 and B) 5 mol% from room temperature up to 1000 �C. L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473468 transition is directly dependent on electric dipole (ED) mecha- nism. This characteristic allows the Eu3þ to be used as a structural probe in several host matrix to understand with more detail about the chemical enviromental around of this one [9]. Due to these specific characteristics of Eu3þ, many efforts have been realized in order to manufacture optical devices by intro- ducing RE3þ in many kind of host matrix. Many papers have been presented in the literature showing that Gd2O3 is a promising oxide for the application as a host matrix for doping with RE3þ due to its particular chemical properties, photochemical and good photo- thermal stability, and its low-energy phonons related to the Gd-O chemical bonding [10]. The Gd2O3 is a versatile material with high potential for application in many fields of technology ranging from the development of corrosion-resistant coatings, due to their thermal stability and refractory properties and scintillation properties. The incorporation of RE3þ into crystalline matrix contribute to the appearance of many kind of imperfections that may affect negatively the photoluminescence spectroscopic properties. The presence of defects and/or microstrains in crystalline structures, can contribute to the appearance of processes that affect directly on photoluminescence process via non-radiative mechanisms. These processes deactivate the excited state in which promotes the reduction of lifetime values, and consequently compromises the quantum yield of the system. In this sense the present work reports on preparation of Eu3þ- doped Gd2O3 via molecular polymeric route using poly- ethyleneglycol (PEG) as a precursor. The photoluminescent, struc- tural and scintillation properties were evaluated in order to ascertain their potentialities for applications in technological devices. 2. Material and methods Eu3þ-doped Gd2O3 with 1, 3, 5, 7 and 10 mol% in powder form were prepared through the polymerization using poly- ethyleneglycol (PEG) as precursor. Gd2O3 and Eu2O3 were dissolved in an aqueous medium containing concentrated hy- drochloric acid to obtain the standard solution, to be used as precursor solution in preparation of all samples. These standard solutions were titrated with EDTA 0.01 mol L�1 at room temper- ature. Five precursor's solution were obtained, where each solu- tion containing the exact ratio of Eu3þ (1, 3, 5, 7 and 10 mol%) in relation to mol amount of Gd3þ were prepared as follow: The exact volume of each solution containing Eu3þ and Gd3þ was pipetted into a beaker (Solution 1). Into another container, the mass of PEG was added corresponding to 10 times the sum of the moles of both metals ([Gd3þþEu3þ]) and dissolved in deionized water (Solution 2). Then both solutions were mixed, Solution 1 and Solution 2. The mixed solutions were kept under stirring, approximately 150 rpm at 80 �C to obtain the viscous solution called precursors solutions. The thermal behavior of all the pre- cursors solutions with different concentrations of Eu3þ were analyzed by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) using the thermobalance Shimadzu, model DTG-60H under synthetic air atmosphere under heating rate of 10 �C/min, from 25 up to 1000 �C. Based on thermal behavior observed, the precursor solutions were heat-treated at 900, 1000 and 1100 �C for 4 h in an oven (EDG model 1800) under an air atmosphere. During the heat-treatment, the conditions were kept the same as those used during TGA and DTA analysis. The materials obtained after the heat treatments were charac- terized by X-Ray diffraction (XRD), operating a Shimadzu diffractometer, Ka of Cu radiation, l ¼ 1.5418 Å, graphite mono- chromator, step of 0.02 degrees between 2q ¼ 10�e80�. Based on the diffractograms obtained, the Scherrer's equation was used to estimate the crystallite size of crystal structure and the microstrains were evaluated by Willianson-Hall (WeH) method. The materials were also characterized by Raman spectroscopy using Raman spectrophotometer LabRam-HR with excitation source at 632.8 nm. Photoluminescence properties were carried out at room temperature using a Fluorolog spectrofluorometer SPEXF2121/Jobin-Yvon with excitation source at 255 nm, with filter cut-off bellow 399 nm. The excitation and emission slits were 5 and 2 nm, respectively. The decay curves of the excited state of the materials were obtained using a Fluorolog spectro- fluorometer SPEXF2121/Jobin-Yvon with excitation and emission fixed at 255 nm and 611 nm, respectively. The excitation and emission slits, were the same reported above. The samples were crushed in an agate mortar with 100 mg of KBr, and submitted under a pressure of 10 tons for 1 min to obtain the pellets. The pellets were characterized by Fourier Transform Infra-Red (FTIR) spectroscopy operating a Perkin Elmer spectrometer (Spectrum GX) in transmission mode recording 32 spectrums with a reso- lution of 4 cm�1. For the emission spectra under X-ray excitation was used the X-ray diagnostic equipment with 100 kV (energy 100 kev) ma CR 100 e 7/100 e SHR, optical fiber with 400 microns localized at 3 mm from the sample and a spectrometer Sovereign UV/Visible. The frequency energy used is around 2.2 � 1019. 3. Results and discussion Fig. 1(A) and (B) show TGA analysis showing the efficiency of sintering and the elimination of species from the organic com- pound, PEG, used as precursors. As seen in Fig. 1(A), the process for obtaining material takes place in four stages, in which both L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473 469 endothermic and exothermic events. The first loss of mass of about 12% occurs in approximately 67 �C and can be attributed to the loss of water present in the precursor solutions. The second step, at about 385 �C, as well the third stage (between 420 and 510 �C), show significant loss of mass around 80%. The weight loss is attributed to the elimination of organic matter from PEG used as precursor in the synthesis of materials [11]. At approximately 520 �C, an endothermic peak in a single step is assigned to the elimination of residues still present, presumable from organic Fig. 2. Diffractograms of Eu3þ-doped materials heat-treated at: (A) 900 �C, (B) 1000 �C and (C) 1100 �C for 4 h in air atmosphere. matter strongest linked on surface of material formed. The forma- tion of Gd2O3 crystalline phase can be obtained in temperatures above 700 �C, because any endothermic or exothermic events and loss of mass is observed in this range. Increasing the concentration of Eu3þ, Fig. 1(B), thermal behavior remains the same evenwhere it is observed in the same steps. The total loss of mass for full for- mation of material, approximately 98%, is due to the full elimina- tion of the PEG precursor. A large mass of PEG was used in these work to promote a maximum homogeneity among metals as possible in precursor solution to promote the composition of the final material to be well dispersed. Thus, this detail can contributes to the homogeneous distribution of RE3þ in the final material in order to obtain a maximum efficiency of photoluminescent prop- erties. To make sure no residue of organic matter present in the final material, heat-treatment temperatures that the samples were submitted were 900, 1000 and 1100 �C. From the analysis of XRD was possible to evaluate the crystal- linity of the materials obtained at different heat-treatments, and Fig. 2(A)e(C) show the XRD patterns of the materials obtained at 900, 1000 and 1100 �C. According to the XRD patterns obtained, all materials are well crystalline. The reflections observed were assigned to the (hkl) planes with Miller indices equal: (211), (222), (400), (440) and (622) located at 2Q ¼ 20.1�, 28.6�, 33.1�, 47.5� and 56.4�, respectively. The planes observed are atributted to the cubic crystal structure of Gd2O3 in accordance to the JCPDF cards number 00-012-0797. No other phase was observed in the diffractograms with different concentrations of Eu3þ, and temperatures of obtaining, indicating that this route promotes the insertion of this ion into the matrix of Gd2O3 with quite easily. Based on the diffraction patterns of the samples heat-treated at 900 and 1100 �C, the average crystallite size by Scherrer's equation (Equation (1)) were determined. In the Scherrer's equation, D is the crystallite size, K is the shape factor and this work was used 0.89, l is the wave- length of X-Ray radiations used in the analysis (Cu� Ka ¼ 1.5418 Å), and the b in the Full Width Half Maximum (FWHM) of the most intense reflection, and in this case we used the reflection assigned to the (222) planes located at 2Q ¼ 28.6� [12]. Dhkl ¼ Kl bcosq (1) The crystallite size values are shown in Table 1. The microstrains were determined using Williansom-Hall as described in Equation Table 1 Crystallite size values obtained by the Scherrer's equation. Heat-treatment temperature (�C) Samples (mol% of Eu3þ) Crystallite size (nm) 900 1 34.8 5 38.16 10 29.13 1100 1 35 5 44.53 10 40.32 Table 2 Microstrain obtained by Williamson-Hall. Heat-treatment temperature (�C) Samples (mol% of Eu3þ) Microstrains (�10�3) 900 1 1.04 5 1.34 10 1.12 1100 1 1.30 5 1.10 10 1.15 Fig. 4. Raman Spectra of Eu3þ-doped Gd2O3 obtained at 1000 �C with 1, 5 and 10 mol %. L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473470 (2). Initially this method consists in plotting a graph of 4senq along the x-axis along bhklcosq the y-axis. From a linear fit to the data, the ε microstrain is obtained from the slope of the fit [13]. bhklcosq ¼ K:l D þ 4ε sinq (2) Themicrostrain values obtained are shown in Table 2 and do not show significant differences each other. This may be related to the stability of the crystallite size. Another important point that need to be taken into account is that the presence of Eu3þ does not promote significant changes in the crystalline structure of Gd2O3. The values of the ionic radii for the Gd3þ and Eu3þ with coordination number values equal to 6 are 1.078 Å and 1.087 Å, respectively. The simi- larity between the ionic radii for both ions favors the inclusion of large amounts of Eu3þ within the Gd2O3 structure without bringing significant changes in the crystalline system. The materials obtained at higher temperatures of heat-treat- ment, 1100 �C, were submitted to FTIR analysis, and the results are shown in Fig. 3. These samples have been chosen because in pre- vious work it was observed that at higher temperatures of heat- treatment, there is a lower presence of �OH, or other groups that acts like photoluminescence quenchers. All materials presents bands at 410 cm�1 and 540 cm�1 that can be associated with the chemical bonding stretching of nGd-O groups [14,15]. This is an indication of the formation of Gd2O3 solid network. Bands localized around 3400 cm�1 are assigned to the stretching of OeH groups. These groups are still present in the samples heat-treated at 1100 �C for 4 h, but increasing the Eu3þ concentration promotes the decreasing of the intensity of this band. Thus, the presence of this ion can contribute to the elimination of this species. The bands located around 1525 and 1397 cm�1 are assigned to the stretching of the C]O and CeO groups, respectively. These groups may have been formed during the heat-treatment in which the atmosphere contains carbon released during organic precursor decomposition and could be forming bonds with O2� localized on surface of the Gd2O3 particles. The bands localized around 1710 cm�1 can be assigned to the carboxyl groups. In accordance to the Nakamoto, 1986, the carboxyl groups have vibrational stretch- ing mode localized between 1730 e 1700 cm�1 [16]. These bands indicate the presence of these species located on surface of the Eu3þ-doped Gd2O3 particle. Vibration mode of species like C]O and CeO groups and carboxyl can be observed basicaly only by FTIR analysis. Although the TG and DTA analysis show the complete Fig. 3. FTIR spectra of Eu3þ-doped Gd2O3 obtained at 1100 �C for 4 h. decomposition of organic matter and obtaining of Gd2O3 crystalline phase occurs above 700 �C. The Fig. 4 show the Raman spectra of sample heat-treated at 1000 �C. The bands localized at 117, 360, 442 and 565 cm�1 are associated to the cubic phase of Gd2O3 compatible to commercial oxide of the same phase [17]. These results also show the formation of a single crystalline phase of Gd2O3 oxide without the presence of secondary phases. The more intense band at about 360 cm�1 is associated with Eg þ Fg mode being the most intense band of the cubic phase with space group Ia3 stage (206) of Gd2O3 [18,19] cor- responds to the results obtained and showed in this work by XRD. The intensity of band located at 117 cm�1 changes as a function of Eu3þ. This indicates that this ion may be causing a little change in the chemical bonds, but does not cause significant changes in spectroscopic and structure properties. The materials obtained were submitted to photoluminescence spectroscopy under excitation source at 255 nm. The photo- luminescence emission spectra are show in Fig. 5(A), (B) and (C). All samples containing Eu3þ showed an intense red emission observed by naked eye and the transitions attributed to the 5D0/ 7FJ (J¼ 0, 1, 2, 3, 4). All transitions observed in the emission spectra are char- acteristic of Eu3þ with the most intense band localized around 611 nm ascribed to transition 5D0/ 7F2. This transition is allowed by the electric dipole (ED) and only occurs when the Eu3þ ions are located in the site of symmetry with absence of inversion center (i). The band localized around 581 nm is assigned to the 5D0/ 7F0 transition. The bands localized between 585 and 603 nm are assigned to the transitions 5D0/ 7F1 of the Eu3þ. This band is assigned to the transition of Eu3þ allowed by the magnetic dipole (MD), where the intensity of this transition does not depend on environment where the RE3þ is localized. The bands located be- tween 645 and 670 and the band located between 681 and 719 are assigned to the 5D0/ 7F3 and 5D0/ 7F4, respectively. It appears that the materials obtained here exhibit an intense absorption in the ultraviolet regionwhich is converted to intense emission in the red region. It can be observed in Fig. 6 that samples with higher relative emission intensity, though not as intense as others, were those heat-treated at 1100 �C. The decay curves of the excited state of the transition 5D0 were also obtained fixing the excitation and emission at 255 and 611 nm, respectively. Fig. 7 shows the decay curve of the sample containing 7 mol% of Eu3þ heat treated at 1100 �C that is repre- sentative for all samples obtained in this work. The values ob- tained are shown in Table 3. The decay curves were fitted to a first L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473 471 order exponential decay with values of R of around 0.999. The values of lifetime were between 2.84 and 2.89 ms noting that there was no great change with increasing of Eu3þ concentration in the system, as well as with increasing temperature heat- treatment. Practically it is not observed change in the values of Fig. 5. Photoluminescence emission spectra of Eu3þ-doped Gd2O3 heat treated at (A) 900, (B) 1000 and (C) 1100 �C for 4 h under excitation at 255 nm. lifetime. This effect can be related to the low microstrain observed in this work and also the similarity of ionic radii be- tween Eu3þ and Gd3þ, causing no significant changes in the crystal lattice. Even if the materials showed groups such as OeH, CeH, C]H, and carboxyl groups, which act as a deactivator excited states of the RE3þ, showed intense photoluminescence emission and relative long lifetime values of the excited state 5D0 of the Eu3þ in the materials obtained here. Lifetime values ob- tained suggest that the Eu3þ are located inside of the crystal lattice, protected from the groups located on particle surface Fig. 6. Maximum intensity of photoluminescence on the transition 5D0/ 7F2 of the materials obtained. Fig. 7. Photoluminescence decay curve of 5D0 excited state of Eu3þeGd2O3 heat- treated at 1100 �C for 4 h. Table 3 Lifetime values of the excited state 5D0. Heat-treatment temperature (�C) Samples(mol% of Eu3þ) Lifetime (ms) 900 1 2.88 5 2.86 10 2.85 1100 1 2.87 5 2.84 10 2.89 Fig. 8. Photoluminescence emission spectra of Eu3þ-doped Gd2O3 heat treated at (A) 900, (B) 1000 and (C) 1100 �C for 4 h under excitation with X-ray source. L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473472 avoiding loss via non-radiative process. In order to evaluate the possibility of application as a scintillator, the materials obtained were excited using X-rays radiation, and the results are shown in Fig. 8(A)e(C). All materials when excited with X-ray source showed intense emission in the red region assigned to the Eu3þ transitions. Themost intense emission is located at 611 nm associated with the transition 5D0/ 7F2 4. Conclusions In summary the results showed that the route chosen for obtaining these materials was success. The heat-treatment tem- perature chosen showed significant results on the formation of the crystalline phase of the materials. The heat-treatment tempera- tures do not have significant impact on the values of microstrain and on the crystallites size. The concentrations of Eu3þ added in the system also no caused structural variation assigned to the similarity between the ionic radii of the Eu3þ and Gd3þ. Even the presence of functional groups and species that may contribute to the deactivation of the excited state still maintained an intense photoluminescence and long lifetime values of the excited state, suggesting the inclusion of RE3þ within the host matrix protects it from groups located on surface. When the material was excited by X-ray radiation, intense emission in the red region was observed, suggesting that this material has potential for application in scintillators devices. Acknowledgments The authors would like to acknowledge FAPEMIG, FAPESP, CAPES, and CNPq. This work is a collaboration research project of members of the Rede Mineira de Química (RQ-MG) supported by FAPEMIG (Project: REDE-113/10). The authors also acknowledge Jenifer Esbenshade for English revisions. References [1] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag, Berlin, 1994. [2] R.V. Perrella, D.P. dos Santos, G.Y. Poirier, M.S. G�oes, S.J.L. Ribeiro, M.A. Schiavon, J.L. Ferrari, Er3þ-doped Y2O3 obtained by polymeric precursor: synthesis, structure and upconversion emission properties, J. Lumin 149 (2014) 333e340. [3] J.L. Ferrari, K. de Oliveira Lima, E. Pecoraro, R.A.S. Ferreira, L.D. Carlosc, R.R. Gonçalves, Color tunability of intense upconversion emission from Er3þeYb3þ co-doped SiO2eTa2O5 glass ceramic planar waveguides, J. Mater. Chem. 22 (2012) 9901e9908. [4] J.L. Ferrari, K.O. Lima, L.J.Q. Maia, S.J.L. Ribeiro, A.S.L. Gomes, R.R. Gonçalves, Broadband NIR emission in SoleGel Er3þ-Activated SiO2eTa2O5 glass ceramic planar and channel waveguides for optical application, J. Nanosci. Nano- technol. 11 (2011) 2540e2544. [5] L.A. Rocha, M.A. Schiavon, C.S. Nascimento Jr., L. Guimar~aes, M.S. G�oes, A.M. Pires, C.O. Paiva-Santos, O.A. Serra, M.A. Cebim, M.R. Davolos, J.L. Ferrari, Sr2CeO4: Electronic and structural properties, J. Alloy Compd. 608 (2014) 73e78. [6] J.L. Ferrari, M.A. Cebim, A.M. Pires, M.A. Couto dos Santos, M.R. Davolos, Y2O3: Eu3þ (5 mol%) with Ag nanoparticles prepared by citrate precursor, J. Solid State Chem. 183 (2010) 2110e2115. [7] J.L. Ferrari, A.M. Pires, O.A. Serra, M.R. Davolos, Luminescent and morpho- logical study of Sr2CeO4 blue phosphor prepared from oxalate precursors,, J. Lumin 131 (2011) 25e29. [8] O.L. Malta, Theoretical crystal-field parameters for the YOC1-Eu3þ system e A simple overlap model, Chem. Phys. Lett. 88 (1982) 353e356. [9] K. Driesen, V.K. Tikhomirov, C. Gorller-Walrand, Eu3þ as a probe for rare-earth dopant site structure in nano-glass-ceramics, J. Appl. Phys. V. 102 (2007) 24312. [10] J.L. Ferrari, R.L.T. Parreira, A.M. Pires, S.A.M. Lima, M.R. Davolos, A route to obtain Gd2O3:Nd3þ with different particle size, Mater. Chem. Phys. 127 (2011) 40e44. [11] H. Guo, N. Dong, M. Yinm, L. Lou, S. Xia, Visible upconversion in rare earth ion- Doped Gd2O3 Nanocrystals, J. Phys. Chem. B 108 (2004) 19205e19209. [12] Li-Ling Ooi, Principles of X-ray Crystallography, Oxford University Press, Ox- ford, 2010. [13] V.D. Mote, Y. Purushotham, B.N. Dole, Willianson-Hall analysis in estimations of lattice strain in nanometer-sized ZnO particles, J. Theor. Appl. Phys. 6 (2012) 1e8. [14] N. Dhananjaya, H. Nagabhushana, B.M. Nagabhushana, B. Rudraswamy, C. Shivakumara, R.P.S. Chakradhar, Hydrothermal synthesis, characterization and Raman studies of Eu3þ activated Gd2O3 nanorods, Phys. B 406 (2011) 1639e1644. [15] N. Dhananjaya, H. Nagabhushana, B.M. Nagabhushana, B. Rudraswamy, C. Shivakumara, R.P.S. Chakradhar, Spherical and rod-like Gd2O3:Eu3þ nano- phosphorsdstructural and luminescent properties, Bull. Mater. Sci. 35 (2012) 519e527. [16] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination http://refhub.elsevier.com/S0925-8388(15)30346-7/sref1 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref2 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref3 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref4 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref5 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref6 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref7 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref8 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref8 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref8 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref8 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref8 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref9 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref9 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref9 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref9 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref10 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref11 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref11 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref11 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref11 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref11 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref12 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref12 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref13 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref13 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref13 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref13 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref14 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref15 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref16 L.P.B. Durante et al. / Journal of Alloys and Compounds 648 (2015) 467e473 473 Compounds, fifth ed., John Wiley & Sons, Inc., New York, 1997. [17] A. García-Murillo, A. Le Luyer, C. Dujardin, C. Pedrini, J. Mugnier, Elaboration and characterization of Gd2O3 waveguiding thin filmes prepareted by the sol- gel process, Opt. Mater. 16 (2001) 39e46. [18] G. Rajan, K.G. Gopchandran, Engineering of luminescence from Gd2O3:Eu3þ nanophosphors by pulsed laser deposition, Opt. Mat. 32 (2009) 121e132. [19] G. Rajan, K.G. Gopchandran, Enhanced luminescence from spontaneously ordered Gd2O3:Eu3þ based nanostructures, Appl. Surf. Sci. 255 (2009) 9112e9123. http://refhub.elsevier.com/S0925-8388(15)30346-7/sref16 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref16 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref17 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref18 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref18 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref18 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 http://refhub.elsevier.com/S0925-8388(15)30346-7/sref19 Synthesis, characterization and evaluation of scintillation properties of Eu3+-doped Gd2O3 obtained using PEG as precursor 1. Introduction 2. Material and methods 3. Results and discussion 4. Conclusions Acknowledgments References