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Structural And Photoluminescence Studies Of Europium Doped Mgo Nanoparticles Synthesized By Polyol Technique
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 3 (2016) 4249–4253
www.materialstoday.com/proceedings
ICMRA 2016
Structural And Photoluminescence Studies Of Europium Doped Mgo Nanoparticles Synthesized By Polyol Technique K.Ramachandra Rao*, D.Vijay#, K.Sujatha, Ch.Satya Kamal, T.Samuel and Sk. E.Basha Crystal Growth and Nanoscience Research Centre, Department of Physics, Government College (A), Rajamahendravaram-533105, Andhra Pradesh, India #Project Fellow, II M..Sc (Physics), Government College (A), Rajamahendravaram--533105, Andhra Pradesh, India
Abstract MgO:Eu3+(1-3 at%) nanoparticles were synthesized by using polyol mediated technique. Powder XRD for phase conformation, Scanning Electron Microscopy (SEM) analysis for surface morphology and Photoluminescence (PL) emission under UV excitation were recorded with prepared nanoparticles. Powder XRD data revealed the formation of cubic system. The observed visible emission peaks are due to the energy transfer between MgO and Eu 3+ ions. Quenching is observed as dopant concentration increases. The color of PL emission peaks are identified using CIE coordinates. © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International conference on materials research and applications-2016. Keywords:MgO:Eu3+ nanoparticles; Polyol; XRD; SEM; PL studies
1. INTRODUCTION MgO is a well-known photo catalyst with unique chemical, mechanical, optical and electrical properties; inexpensiveness and nontoxicity were identified as the main reason for the acceptability of MgO materials. The luminescence properties of rare earth doped MgO NPs depends on various factors such as phase purity, crystallite size, surface morphology, nature of dopants and thesynthesis route [1, 2]. Several physical and chemical procedures were used for the synthesis of large quantities of metal NPs in relatively short period of time. Approaches such as co-precipitation method and hydrothermal method [3, 4] were widely used. However, among all, the Polyol method is one of the more widely recognized methods due to its several advantages like soft chemistry, easy to handle and * Corresponding author. Tel.: +91-0883-2428736; E-mail address: [email protected] 2214-7853© 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International conference on materials research and applications-2016.
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requiring no special or expensive equipment [5]. In the present study, we have synthesized Eu doped MgO nanoparticles by simple polyol method and the work was focussed to estimate the structural and luminescence properties of the synthesized material. 2. EXPERIMENTAL PROCEDURE 1 at% Eu-doped MgO Nano particles were synthesized by a simple and low cost Polyol method using Magnesium nitrate, Europium nitrate (SDFINE –CHEM LIMITED) as starting materials. Ethylene glycol was used as a solvent and stabilizing ligand. A required amount of Magnesium nitrate and 1 at% europium nitrate are added in 20 ml of ethylene glycol. Solution was shaken and kept under stirring. When the temperature was raised to 100 oC, followed by the addition of appropriate amount of urea and further temperature was raised to 120 oC and maintained at this temperature for 2 hours. The precipitate obtained after 2 h of reaction was cooled, centrifuged, washed twice with methanol, and twice with acetone. The precipitate was dried overnight under ambient conditions. The samples prepared thus were finally heated to 900 oC for 5 hours.
3. RESULTS AND DISCUSSION 3.1. Powder X-ray Diffraction Analysis Fig.1 shows XRD pattern of MgO : Eu 1at%consists of sharp peaks characteristic of cubic structure. The lattice parameter have been calculated based on the least square fitting of the diffraction peaks and found to be a=4.203 A o which matches well with that reported earlier (PC-PDF-75-0447). The average crystallite size has been calculated from the line width of the XRD peak ((200) reflection) and found to be around 23.88 nm.
Figure 1: X-ray diffraction pattern of the Eu3+ doped MgO nanoparticles.
3.2. Scanning Electron Microscopy (SEM) The surface morphology of pure MgO and MgO: Eu3+ (1 mol %) nanoparticles studied through SEM analysis were shown in Fig-:2(a) & (b).The MgO: Eu3+nanoparticles showed non-uniform size with nearly spherical shape. The crystallite size estimated from XRD and SEM measurements were in good agreement.
K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
a
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b
Fig. 2 (a) SEM micrographs of the pure; (b) and Eu3+ doped MgO nanoparticles at 900 oC
3.3. Photoluminescence Studies It is well known that there are two kinds of emission bands of UV and visible spectrum in MgO nanoparticles. Zhang et al. reported band around 383 nm in the PL emission spectrum of MgO nanobelts[6], which has been proposed originating from the contribution of oxygen vacancies in the MgO host. The emission peaks (Fig. 3(a))of 900 oC heated MgO:Eu3+ (1-3 at%) sample in the range around 420 nm (bluish-violet region) was attributed to surface defects namely oxygen vacancies, F- centres (oxygen ion vacancy occupied by two electrons) / F +-centres (oxygen ion vacancy occupied by single electrons) / surface states of the host material [7-9].When Eu3+ ions were doped into the host, they could probably occupy Mg site possesses inversion symmetry. Owing to the different ionic radii for the Mg2+ and Eu3+, oxygen vacancies are formed to balance the charge difference. The excess amount of europium will likely reside on either surface of the nanoparticles to yield optimum strain relief. From the emission spectra of MgO:Eu3+ (1-3 at%) nanoparticles on excitations at 267 nm (indirect excitation through MgO) shows a strong luminescence at 617 nm (5 D0 - 7 F2). This indicates that the energy transfer is taking place between MgO and Eu3+ ions. The luminescence intensities of the MgO: Eu3+(1 and 2 at %) phosphors increases with the increase of Eu3+ ion concentration. As and when concentration reaches above 2 at % intensity decreases due to energy transfer among the excited Eu3+ ions at higher concentrations and also due to concentration quenching. Hence, the quenching of luminescencemay also occur as a result of cross-relaxation processes in close Eu3+– Eu3+ pairs. Fig. 3(b) shows the excitation spectra of MgO:Eu3+ nanoparticles monitored at 617 nm emission. The peaks observed around 360, 377 and 393 nm are characteristic of intra 4f transitions of Eu 3+ ions. The peak corresponding to the Eu–O chargetransfer process normally observed around 270 nm is observed. Main reason affecting the intensity of the charge transfer band (CTB) was the efficiency of the energy process from O 2−➔Eu3+charge transfer band (CTB) to the Eu3+emitting level. The corresponding bi-exponential decay of MgO: Eu3+ (1-3 at %) shown in Fig. 4(a, b, c). Life time values also decreases above 2 at% doping of Eu3+concentration. MgO: Eu3+ 1% (0.98 ms), MgO: Eu3+ 1% (2.4 ms) and MgO: Eu3+ 1% (0.72 ms).
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K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
a
b
Fig. 3 (a) Emission; (b) excitation spectra of MgO: Eu3+(1-3 at %) 900 oC heated samples.
3.4. Decay Curves
a b
c
Fig.4(a); (b) and (c)Life time decay curves of MgO:Eu3+(a) 1% (b) 2% (c) 3 at% 900oC heated samples.
K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
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3.5. Color Coordinates
Fig.5 shows the CIE chromaticity color coordinates of PL emissions from MgO: Eu (1-3%) phosphor powder samples. A (0.37, 0.22), B (0.35, 0.22), and C (0.33, 0.22)900 oC heated samples.
4. CONCLUSIONS Eu3+ (1-3 at%) doped MgO nanoparticles were synthesized by Polyol mediated technique. The phase formation, morphological studies were confirmed by XRD and scanning electron microscopy (SEM). Based on the steady-state luminescence effects, it has been concluded that there exists a strong energy transfer between the host MgO and Eu3+ ion in MgO:Eu3+ nanoparticles. Luminescence quenching is observed as dopant concentration increases. Acknowledgements The authors are grateful to Dr. P. Syam Prasad, NIT-Warangal for providing XRD and SEM studies. We thank Dr.V.Sudarsan, BARC,Mumbaifor PL studies.Our sincere gratitude to Dr.Ch.Masthanaiah, Principal, Govt.College(A), Rajamahendravaram for providing necessary research lab facilities.
References [1] Y. Huang, S. Ou, G. Xu, M. Fang, X.Z. Li, Appl. Surf. Sci. 254 (2008) 2013–2016. [2] P. Mishra, R.S. Yadav, A.C. Pandey, Ultrason. Sonochem17 (2010) 560–565. [3] K. Sato, F. Sag, K. Nagaoka, Y. Takita, Int. J. Hydrogen Energy 35 (2010) 5393–5399. [4] H.R. Mahmoud, S.A. El-Molla, M. Saif, Powder Technol. 249 (2013) 225–233. [5] NoriyaIzu, Kazuhiko Shimada, TakafumiAkamatsu, Toshio Itoh, Woosuck Shin,KentaroShiraishi, TaketoshiUsui, Ceramics International 40 (2014) 8775-8781. [6] J. Zhang, L.D. Zhang, Chem. Phys. Letts 363 (2002) 293. [7] P.B. Devaraja, D.N. Avadhani, S.C. Prashantha, H. Nagabhushana, S.C. Sharma, B.M.Nagabhushana, H.P. Nagaswarupa, Spectr. Acta Part A: Molec. Biom.Spectr. 118 (2014) 847–851. [8] T. Yanagida, K. Nagashima, H. Tanaka, T. Kawai, J. Appl. Phys. 104 (2008)016101-016103. [9] P.B. Devaraja, D.N. Avadhani, H. Nagabhushana, S.C. Prashantha, S.C. Sharma, B.M. Nagabhushana, H.P. Nagaswarupa, B. DharukaPrasadMaterials Characterization,97 (2014) 27–36.
ScienceDirect Materials Today: Proceedings 3 (2016) 4249–4253
www.materialstoday.com/proceedings
ICMRA 2016
Structural And Photoluminescence Studies Of Europium Doped Mgo Nanoparticles Synthesized By Polyol Technique K.Ramachandra Rao*, D.Vijay#, K.Sujatha, Ch.Satya Kamal, T.Samuel and Sk. E.Basha Crystal Growth and Nanoscience Research Centre, Department of Physics, Government College (A), Rajamahendravaram-533105, Andhra Pradesh, India #Project Fellow, II M..Sc (Physics), Government College (A), Rajamahendravaram--533105, Andhra Pradesh, India
Abstract MgO:Eu3+(1-3 at%) nanoparticles were synthesized by using polyol mediated technique. Powder XRD for phase conformation, Scanning Electron Microscopy (SEM) analysis for surface morphology and Photoluminescence (PL) emission under UV excitation were recorded with prepared nanoparticles. Powder XRD data revealed the formation of cubic system. The observed visible emission peaks are due to the energy transfer between MgO and Eu 3+ ions. Quenching is observed as dopant concentration increases. The color of PL emission peaks are identified using CIE coordinates. © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International conference on materials research and applications-2016. Keywords:MgO:Eu3+ nanoparticles; Polyol; XRD; SEM; PL studies
1. INTRODUCTION MgO is a well-known photo catalyst with unique chemical, mechanical, optical and electrical properties; inexpensiveness and nontoxicity were identified as the main reason for the acceptability of MgO materials. The luminescence properties of rare earth doped MgO NPs depends on various factors such as phase purity, crystallite size, surface morphology, nature of dopants and thesynthesis route [1, 2]. Several physical and chemical procedures were used for the synthesis of large quantities of metal NPs in relatively short period of time. Approaches such as co-precipitation method and hydrothermal method [3, 4] were widely used. However, among all, the Polyol method is one of the more widely recognized methods due to its several advantages like soft chemistry, easy to handle and * Corresponding author. Tel.: +91-0883-2428736; E-mail address: [email protected] 2214-7853© 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International conference on materials research and applications-2016.
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K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
requiring no special or expensive equipment [5]. In the present study, we have synthesized Eu doped MgO nanoparticles by simple polyol method and the work was focussed to estimate the structural and luminescence properties of the synthesized material. 2. EXPERIMENTAL PROCEDURE 1 at% Eu-doped MgO Nano particles were synthesized by a simple and low cost Polyol method using Magnesium nitrate, Europium nitrate (SDFINE –CHEM LIMITED) as starting materials. Ethylene glycol was used as a solvent and stabilizing ligand. A required amount of Magnesium nitrate and 1 at% europium nitrate are added in 20 ml of ethylene glycol. Solution was shaken and kept under stirring. When the temperature was raised to 100 oC, followed by the addition of appropriate amount of urea and further temperature was raised to 120 oC and maintained at this temperature for 2 hours. The precipitate obtained after 2 h of reaction was cooled, centrifuged, washed twice with methanol, and twice with acetone. The precipitate was dried overnight under ambient conditions. The samples prepared thus were finally heated to 900 oC for 5 hours.
3. RESULTS AND DISCUSSION 3.1. Powder X-ray Diffraction Analysis Fig.1 shows XRD pattern of MgO : Eu 1at%consists of sharp peaks characteristic of cubic structure. The lattice parameter have been calculated based on the least square fitting of the diffraction peaks and found to be a=4.203 A o which matches well with that reported earlier (PC-PDF-75-0447). The average crystallite size has been calculated from the line width of the XRD peak ((200) reflection) and found to be around 23.88 nm.
Figure 1: X-ray diffraction pattern of the Eu3+ doped MgO nanoparticles.
3.2. Scanning Electron Microscopy (SEM) The surface morphology of pure MgO and MgO: Eu3+ (1 mol %) nanoparticles studied through SEM analysis were shown in Fig-:2(a) & (b).The MgO: Eu3+nanoparticles showed non-uniform size with nearly spherical shape. The crystallite size estimated from XRD and SEM measurements were in good agreement.
K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
a
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b
Fig. 2 (a) SEM micrographs of the pure; (b) and Eu3+ doped MgO nanoparticles at 900 oC
3.3. Photoluminescence Studies It is well known that there are two kinds of emission bands of UV and visible spectrum in MgO nanoparticles. Zhang et al. reported band around 383 nm in the PL emission spectrum of MgO nanobelts[6], which has been proposed originating from the contribution of oxygen vacancies in the MgO host. The emission peaks (Fig. 3(a))of 900 oC heated MgO:Eu3+ (1-3 at%) sample in the range around 420 nm (bluish-violet region) was attributed to surface defects namely oxygen vacancies, F- centres (oxygen ion vacancy occupied by two electrons) / F +-centres (oxygen ion vacancy occupied by single electrons) / surface states of the host material [7-9].When Eu3+ ions were doped into the host, they could probably occupy Mg site possesses inversion symmetry. Owing to the different ionic radii for the Mg2+ and Eu3+, oxygen vacancies are formed to balance the charge difference. The excess amount of europium will likely reside on either surface of the nanoparticles to yield optimum strain relief. From the emission spectra of MgO:Eu3+ (1-3 at%) nanoparticles on excitations at 267 nm (indirect excitation through MgO) shows a strong luminescence at 617 nm (5 D0 - 7 F2). This indicates that the energy transfer is taking place between MgO and Eu3+ ions. The luminescence intensities of the MgO: Eu3+(1 and 2 at %) phosphors increases with the increase of Eu3+ ion concentration. As and when concentration reaches above 2 at % intensity decreases due to energy transfer among the excited Eu3+ ions at higher concentrations and also due to concentration quenching. Hence, the quenching of luminescencemay also occur as a result of cross-relaxation processes in close Eu3+– Eu3+ pairs. Fig. 3(b) shows the excitation spectra of MgO:Eu3+ nanoparticles monitored at 617 nm emission. The peaks observed around 360, 377 and 393 nm are characteristic of intra 4f transitions of Eu 3+ ions. The peak corresponding to the Eu–O chargetransfer process normally observed around 270 nm is observed. Main reason affecting the intensity of the charge transfer band (CTB) was the efficiency of the energy process from O 2−➔Eu3+charge transfer band (CTB) to the Eu3+emitting level. The corresponding bi-exponential decay of MgO: Eu3+ (1-3 at %) shown in Fig. 4(a, b, c). Life time values also decreases above 2 at% doping of Eu3+concentration. MgO: Eu3+ 1% (0.98 ms), MgO: Eu3+ 1% (2.4 ms) and MgO: Eu3+ 1% (0.72 ms).
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a
b
Fig. 3 (a) Emission; (b) excitation spectra of MgO: Eu3+(1-3 at %) 900 oC heated samples.
3.4. Decay Curves
a b
c
Fig.4(a); (b) and (c)Life time decay curves of MgO:Eu3+(a) 1% (b) 2% (c) 3 at% 900oC heated samples.
K. Ramachandra Rao/ Materials Today: Proceedings 3 (2016) 4249–4253
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3.5. Color Coordinates
Fig.5 shows the CIE chromaticity color coordinates of PL emissions from MgO: Eu (1-3%) phosphor powder samples. A (0.37, 0.22), B (0.35, 0.22), and C (0.33, 0.22)900 oC heated samples.
4. CONCLUSIONS Eu3+ (1-3 at%) doped MgO nanoparticles were synthesized by Polyol mediated technique. The phase formation, morphological studies were confirmed by XRD and scanning electron microscopy (SEM). Based on the steady-state luminescence effects, it has been concluded that there exists a strong energy transfer between the host MgO and Eu3+ ion in MgO:Eu3+ nanoparticles. Luminescence quenching is observed as dopant concentration increases. Acknowledgements The authors are grateful to Dr. P. Syam Prasad, NIT-Warangal for providing XRD and SEM studies. We thank Dr.V.Sudarsan, BARC,Mumbaifor PL studies.Our sincere gratitude to Dr.Ch.Masthanaiah, Principal, Govt.College(A), Rajamahendravaram for providing necessary research lab facilities.
References [1] Y. Huang, S. Ou, G. Xu, M. Fang, X.Z. Li, Appl. Surf. Sci. 254 (2008) 2013–2016. [2] P. Mishra, R.S. Yadav, A.C. Pandey, Ultrason. Sonochem17 (2010) 560–565. [3] K. Sato, F. Sag, K. Nagaoka, Y. Takita, Int. J. Hydrogen Energy 35 (2010) 5393–5399. [4] H.R. Mahmoud, S.A. El-Molla, M. Saif, Powder Technol. 249 (2013) 225–233. [5] NoriyaIzu, Kazuhiko Shimada, TakafumiAkamatsu, Toshio Itoh, Woosuck Shin,KentaroShiraishi, TaketoshiUsui, Ceramics International 40 (2014) 8775-8781. [6] J. Zhang, L.D. Zhang, Chem. Phys. Letts 363 (2002) 293. [7] P.B. Devaraja, D.N. Avadhani, S.C. Prashantha, H. Nagabhushana, S.C. Sharma, B.M.Nagabhushana, H.P. Nagaswarupa, Spectr. Acta Part A: Molec. Biom.Spectr. 118 (2014) 847–851. [8] T. Yanagida, K. Nagashima, H. Tanaka, T. Kawai, J. Appl. Phys. 104 (2008)016101-016103. [9] P.B. Devaraja, D.N. Avadhani, H. Nagabhushana, S.C. Prashantha, S.C. Sharma, B.M. Nagabhushana, H.P. Nagaswarupa, B. DharukaPrasadMaterials Characterization,97 (2014) 27–36.