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Photoluminescence properties of Eu3+-doped low cost zinc silicate based glass ceramics
Optik 127 (2016) 3727–3729
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Photoluminescence properties of Eu3+ -doped low cost zinc silicate based glass ceramics Nur Alia Sheh Omar a , Yap Wing Fen a,b,∗ , Khamirul Amin Matori a,b a b
Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
a r t i c l e
i n f o
Article history: Received 11 September 2015 Accepted 28 December 2015 Keywords: Eu3+ -doped Zn2 SiO4 Solid state method XRD Photoluminescence
a b s t r a c t In this paper, Zn2 SiO4 :xEu3+ phosphors were synthesized with different concentrations of Eu3+ ions (x = 1, 3 and 5 wt.%) by using waste bottle glasses as silicate source. The structure, morphology, and luminescent properties of the phosphors were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy. The XRD analysis revealed that addition of dopant increased the crystallinity of the samples, and then were decreased dramatically when the dopant concentration further to 5 wt.%. The FESEM images showed the samples have irregular in shapes while their emission and excitation peak of Zn2 SiO4 :xEu3+ phosphor was observed at 600 and 400 nm, respectively. © 2016 Elsevier GmbH. All rights reserved.
1. Introduction Recently, zinc silicate (Zn2 SiO4 ) have been used as host crystals for a large part doping of rare earth ions to achieve excellent luminescent in the blue, green and red spectral zones [1–5]. Many researchers have chosen europium (Eu3+ ) ion as a luminescent centres in a different host, such as LiAl5 O8 :Eu3+ [6], Sr2 MgSi2 O7 :Eu3+ [7], NaBaBO3 :Eu3+ [8] to emit an intense red light which coming from 5 D0 –7 F2 transition. Furthermore, Eu3+ is well known to be promising rare-earth dopants as it has a variety of applications such as optical amplifiers, lasers and electroluminescent devices [9]. In one study, preparation of Eu3+ doped willemite using the melt-quench technique was successfully studied by Tarafder et al., who had used high purity of silicate (SiO2 ) powder which is quite expensive to synthesis this phosphors [10]. Therefore, in order to overcome this drawback, soda lime silica (SLS) glasses are chosen to replace SiO2 source as it can reduce the cost of production and also has advantages as an attractive host matrix for rare earth ions because of its fine optical and mechanical properties, such as good chemical stability, high transparency, low melting point, high thermal stability and good rare- earth ions solubility [11]. In the present work, preparation of the Eu3+ doped Zn2 SiO4 by using low cost
∗ Corresponding author at: Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. Tel.: +60 389466689/+60 128190393; fax: +60 0389454454. E-mail addresses: [email protected], [email protected] (Y.W. Fen). http://dx.doi.org/10.1016/j.ijleo.2015.12.124 0030-4026/© 2016 Elsevier GmbH. All rights reserved.
method has been described and the effect of different concentration of Eu3+ on their structural and luminescence properties is also investigated.
2. Experimental Eu3+ (1, 3, and 5 wt.%) doped Zn2 SiO4 glass ceramics were prepared from a 50 g batch with the starting materials, i.e. ZnO (99.99% Aldrich), SLS waste glass, and Eu2 O3 (99.99% Aldrich) by using the solid state method. All chemicals were mixed via milling process for 24 h using the ball milling jar. Then, the chemical batch was melted in an alumina crucible at 1400 ◦ C in air with heating rate of 10 ◦ C min−1 for 2 h in an electrically heated furnace. Later, the molten mixture was poured into the water to get the transparent of glass fritz. The glass frits were cooled to room temperature and then was crushed and sieved into fine powder about 63 m. Next, the fine powders with an addition of 1.75 wt.% Polyvinyl Alcohol (PVA) as the binders, have been pressed at a pressure of 5 tons for 15 min to form the pellets. After that, all pellets were sintered at 800 ◦ C in the electrical furnace with duration of 2 h to form the glass ceramic compounds [12,13]. X-ray diffraction (XRD) spectrum of the glass ceramic samples were on a Phillips X’pert X-ray Diffractometer and the data were collected over the 2 range 10–80◦ at room temperature. The data then analysed by utilizing software X’pert HighScore. The field emission scanning electron microscopy (FESEM) was carried out on the samples coated with gold (Au) to observe the surface morphology of the obtained glass ceramics using Nova NanoSEM 30 Series
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under high vacuum. The photoluminescence excitation and emission spectra were required at room temperature by using Perkin Elmer LS 55 Fluorescence spectrometer at wavelength of 600 nm and 400 nm, respectively. 3. Results and discussion 3.1. X-ray diffraction analysis The XRD patterns of 1, 3, and 5 wt.% Eu3+ doped Zn2 SiO4 phosphor is shown in Fig. 1. All the diffraction peaks were matched very well with the standard values from the Joint Committee on Powder Diffractions Standards (JCPDS) data card number 37-1485, which can be assigned to willemite (␣-Zn2 SiO4 ). At the same time, a little amount of ZnO phase (JCPDS card No. 36-1451) together with AlNa(SiO4 ) phase (JCPDS card No. 02-0625) were also detected [14–16]. As can be seen from the XRD patterns, the intensity of diffraction peak was increased initially with the increasing of Eu doping from 1 to 3 wt.% and then were decreased on further addition of dopant, indicating a worse crystallinity due to lattice distortion [17].
Fig. 2 illustrates the FESEM image for 1, 3, and 5 wt.% Eu3+ doped Zn2 SiO4 phosphors sintered at 800 ◦ C. It is clearly seen that the surface morphology of particles were found in melted-like form and also having irregular shapes [18]. Thus, the results show that the doping process has a small effect on the morphological features as the sample decrease of the porosity after Eu3+ doping, thereby produce a bit larger ceramics [19]. 3.3. Photoluminescence properties The excitation and emission spectra of Zn2 SiO4 :xEu3+ (x = 1, 3, and 5 wt.%) are shown in Figs. 3 and 4. As seen in Fig. 3, the excitation spectra consist of five distinguished characteristic peaks centred at ∼400, 414, 460, 500, and 527 nm which are all ascribed to the intra-configurationally 4f–4f transitions of Eu3+ ions in this host lattice [20]. The most prominent peak is located at 400 nm which corresponds to the transitions 7 F0 → 5 L6 . In the following, this peak was used to record Eu3+ emission spectra (Fig. 4). The emission spectra under blue light (400 nm) excitation reveal five characteristic emission bands peaking at ∼527 nm, 575 nm, 600 nm, 653 nm, and 725 nm which is coming from 5 D1 → 7 F1 , 5D 5 5 5 7 7 7 7 0 → F1 , D0 → F2 , D0 → F3 , and D0 → F4 electronic transitions of Eu3+ ion, respectively. The intense emission peak located
♣ α-Willemite • Zinc Oxide
♣
Aluminium Sodium Silicate
♣
♣♣
♣♣
♣
♣♣ ♣
♣
450
500
550
Wavelength (nm) Fig. 3. Excitation spectrum of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
at around 600 nm (5 D0 → 7 F2 ) is attributed to the hypersensitive forced electric dipole transitions of Eu3+ which give the red colour in the luminescent signals [21,22]. With the increasing of dopant, the electric dipole transition (5 D0 → 7 F2 ) is much stronger than that of the emission peak at 575 nm (5 D0 → 7 F1 ) which is attributed to
C
♣♣
Intensity (a.u)
♣
• ♣
400
Intensity (a.u)
♣
Intensity (a.u)
Fig. 2. FESEM images of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
3.2. Morphological analysis
B
A
10
20
30
40
50
60
70
80
2θ (degree) Fig. 1. XRD patterns of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
500
550
600
650
700
750
Wavelength (nm) Fig. 4. Emission spectrum of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
N.A.S. Omar et al. / Optik 127 (2016) 3727–3729
magnetic dipole transitions [23]. It is also found that the emission intensity increases systematically with the increasing of Eu3+ ion concentration. 4. Conclusion In this work, Eu3+ (1, 3, and 5 wt.%) doped Zn2 SiO4 glass ceramics were successfully prepared by using the solid state method. The XRD pattern showed that 3 wt.% doping exhibited a good crystallization of willemite phase. Also, the addition of dopant has a small effect on the morphological features as the sample decrease of the porosity after Eu3+ doping. The emission peak of Zn2 SiO4 : xEu3+ was observed at 600 nm under the blue light excitation of 400 nm. Acknowledgements The authors gratefully acknowledge the financial support for this study from the Malaysian Ministry of Education (MOE), Ministry of Science, Technology and Innovation (MOSTI) and Universiti Putra Malaysia (UPM) through the Fundamental Research Grant Scheme (FRGS), Science Fund, and Putra Grant. The laboratory facilities provided by the Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, are also acknowledged. References [1] A. Patra, G.A. Baker, S.N. Baker, Synthesis and luminescence study of Eu3+ in Zn2 SiO4 nanocystals, Opt. Mater. 27 (2014) 15–20. [2] A.G. Joly, W. Chen, J. Zhang, S. Wang, Electronic energy relaxation and luminescence decay dynamics of Eu3+ in Zn2 SiO4 :Eu3+ phosphors, J. Lumin. 126 (2007) 491–496. ´ D.M. Petrovic, ´ M. Nikolic, ´ M.D. Dramicanin, ´ [3] Lj. Ðaˇcanin, S.R. Lukic, Judd–Ofelt analysis of luminescence emission from Zn2 SiO4 :Eu3+ nanoparticles obtained by a polymer-assisted sol–gel method, J. Phys. B: At. Mol. Opt. Phys. 406 (2011) 2319–2322. [4] H. Huang, B. Yan, In situ sol–gel composition of multicomponent hybrid precursor to hexagon-like Zn2 SiO4 :Tb3+ microcrystalline phosphors with different silicate sources, Appl. Surf. Sci. 252 (2006) 2967–2972. [5] H.X. Zhang, C.H. Kam, Y. Zhou, X.Q. Han, S. Buddhudu, Y.L. Lam, C.Y. Chan, Deposition and photoluminescence of sol–gel derived Tb3+ :Zn2 SiO4 films on SiO2 /Si, Thin Solid Films 370 (2000) 50–53. [6] V. Singh, T.K. Gundu Rao, Studies of defects in combustion synthesized europium-doped LiAl5 O8 red phosphors, J. Solid State Chem. 181 (2008) 1387–1392.
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[7] I.P. Sahu, D.P. Bisen, N. Brahme, R.K. Tamrakar, Photoluminescence properties of europium doped di-strontium magnesium di-silicate phosphors by solid state reaction method, J. Radiat. Res. App. Sci. 8 (2014) 104–109. [8] X. Qiao, Y. Cheng, L. Qin, C. Qin, P. Cai, S.I. Kim, H.J. Seo, Coprecipitation synthesis, structure and photoluminescence properties of Eu3+ -doped sodium barium borate, J. Alloys Compd. 617 (2014) 946–951. [9] D.T.M. Huong, N.H. Nam, L.V. Vu, N.N. Long, Preparation and optical characterization of Eu3+ -doped CaTiO3 perovskite powders, J. Alloys Compd. 537 (2012) 54–59. [10] A. Tarafder, A.R. Molla, C. Dey, B. Karmakar, Thermal, structural, and enhanced photoluminescence properties of Eu3+ -doped transparent willemite glass–ceramic nanocomposites, J. Am. Ceram. Soc. 96 (2013) 2424–2431. [11] P. Chimalawong, K. Kirrdsiri, J. Kaewkhao, P. Limsuwan, Investigation on the physical and optical properties of Dy3+ doped soda–lime–silicate glasses, Procedia Eng. 32 (2012) 690–698. [12] N.V. Pillai, V.P.M. Pillai, R. Vinodkumar, I. Navas, V. Ganesan, P. Koshy, Influence of europium oxide doping on the structural and optical properties of pulsed laser ablated barium tungstate thin films, J. Alloys Compd. 509 (2011) 2745–2752. [13] W.J. Zhang, W.L. Feng, Y.M. Nie, Photoluminescence properties of red europium doped calcium tungstate for blue-pumped light emitting diodes, Optik 126 (2015) 1341–1343. [14] Q.Y. Zhang, K. Pita, C.H. Kam, Sol–gel derived zinc silicate phosphor films for full-color display applications, J. Phys. Chem. Solids 64 (2003) 333–338. [15] P.V. Ramakrishna, D.B.R.K. Murthy, D.L. Sastry, White-light emitting Eu3+ dodoped ZnO/Zn2 SiO4 :Mn2+ composite microphosphor, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 125 (2014) 234–238. [16] R.Y. Yang, Y.M. Peng, H.L. Lai, C.J. Chu, B. Chiou, Y.K. Su, Effect of different concentrations of Eu3+ ions on the microstructure and photoluminescent properties of Zn2 SiO4 :xEu3+ phosphors and synthesized with TEOS solution as silicate source, Opt. Mater. 35 (2013) 1719–1723. [17] M. Pal, U. Pal, J.M.G.Y. Jiménez, F.P. Rodríguez, Effects of crystallization and dopant concentration on the emission behaviour of TiO2 : Eu nanophosphors, Nanoscale Res. Lett. 7 (2012) 1–12. [18] K.A. Koparkar, N.S. Bajaj, S.K. Omanwar, A potential candidate for lamp phosphors: Eu3+ activated K2Y2B2O7, Adv. Opt. Technol. 2014 (2014) 1–5. [19] G. Braziulis, R. Stankeviciute, A. Zalga, Sol–gel derived europium doped CaMoO4 :Eu3+ with complex microstructural and optical properties, Mater. Sci. 20 (2014) 90–96. [20] B.P. Singh, A.K. Parchur, R.S. Ningthoujam, A.A. Ansari, P. Singh, S.B. Rai, Enhanced photoluminescence in CaMoO4 :Eu3+ by Gd3+ co-doping, Dalton Trans. 43 (2013) 4779–4789. [21] R.J. Wiglusz, T. Grzyb, A. Watras, P.J. Deren, S. Lis, W. Strek, An impact of sintering temperature and doping level on structural and spectral properties of Eu-doped strontium aluminium oxide, J. Rare Earths 29 (2011) 1105–1110. [22] H.X. Zhang, S. Buddhudu, C.H. Kam, Y. Zhou, Y.L. Lam, K.S. Wong, B.S. Ooi, S.L. Ng, W.X. Que, Luminescence of Eu3+ and Tb3+ doped Zn2 SiO4 nanometer powder phosphors, J. Mater. Chem. Phys. 68 (2011) 31–35. [23] B.P. Singh, Maheshwary, P.V. Ramakrishna, S. Singh, V.K. Sonu, S. Singh, P. Singh, A. Bahadur, R.A. Singh, S.B. Rai, Improved photo-luminescence behaviour of Eu3+ activated CaMoO4 nanoparticles via Zn2+ incorporation, RSC Adv. 5 (2015) 55977–55985.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Photoluminescence properties of Eu3+ -doped low cost zinc silicate based glass ceramics Nur Alia Sheh Omar a , Yap Wing Fen a,b,∗ , Khamirul Amin Matori a,b a b
Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
a r t i c l e
i n f o
Article history: Received 11 September 2015 Accepted 28 December 2015 Keywords: Eu3+ -doped Zn2 SiO4 Solid state method XRD Photoluminescence
a b s t r a c t In this paper, Zn2 SiO4 :xEu3+ phosphors were synthesized with different concentrations of Eu3+ ions (x = 1, 3 and 5 wt.%) by using waste bottle glasses as silicate source. The structure, morphology, and luminescent properties of the phosphors were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy. The XRD analysis revealed that addition of dopant increased the crystallinity of the samples, and then were decreased dramatically when the dopant concentration further to 5 wt.%. The FESEM images showed the samples have irregular in shapes while their emission and excitation peak of Zn2 SiO4 :xEu3+ phosphor was observed at 600 and 400 nm, respectively. © 2016 Elsevier GmbH. All rights reserved.
1. Introduction Recently, zinc silicate (Zn2 SiO4 ) have been used as host crystals for a large part doping of rare earth ions to achieve excellent luminescent in the blue, green and red spectral zones [1–5]. Many researchers have chosen europium (Eu3+ ) ion as a luminescent centres in a different host, such as LiAl5 O8 :Eu3+ [6], Sr2 MgSi2 O7 :Eu3+ [7], NaBaBO3 :Eu3+ [8] to emit an intense red light which coming from 5 D0 –7 F2 transition. Furthermore, Eu3+ is well known to be promising rare-earth dopants as it has a variety of applications such as optical amplifiers, lasers and electroluminescent devices [9]. In one study, preparation of Eu3+ doped willemite using the melt-quench technique was successfully studied by Tarafder et al., who had used high purity of silicate (SiO2 ) powder which is quite expensive to synthesis this phosphors [10]. Therefore, in order to overcome this drawback, soda lime silica (SLS) glasses are chosen to replace SiO2 source as it can reduce the cost of production and also has advantages as an attractive host matrix for rare earth ions because of its fine optical and mechanical properties, such as good chemical stability, high transparency, low melting point, high thermal stability and good rare- earth ions solubility [11]. In the present work, preparation of the Eu3+ doped Zn2 SiO4 by using low cost
∗ Corresponding author at: Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. Tel.: +60 389466689/+60 128190393; fax: +60 0389454454. E-mail addresses: [email protected], [email protected] (Y.W. Fen). http://dx.doi.org/10.1016/j.ijleo.2015.12.124 0030-4026/© 2016 Elsevier GmbH. All rights reserved.
method has been described and the effect of different concentration of Eu3+ on their structural and luminescence properties is also investigated.
2. Experimental Eu3+ (1, 3, and 5 wt.%) doped Zn2 SiO4 glass ceramics were prepared from a 50 g batch with the starting materials, i.e. ZnO (99.99% Aldrich), SLS waste glass, and Eu2 O3 (99.99% Aldrich) by using the solid state method. All chemicals were mixed via milling process for 24 h using the ball milling jar. Then, the chemical batch was melted in an alumina crucible at 1400 ◦ C in air with heating rate of 10 ◦ C min−1 for 2 h in an electrically heated furnace. Later, the molten mixture was poured into the water to get the transparent of glass fritz. The glass frits were cooled to room temperature and then was crushed and sieved into fine powder about 63 m. Next, the fine powders with an addition of 1.75 wt.% Polyvinyl Alcohol (PVA) as the binders, have been pressed at a pressure of 5 tons for 15 min to form the pellets. After that, all pellets were sintered at 800 ◦ C in the electrical furnace with duration of 2 h to form the glass ceramic compounds [12,13]. X-ray diffraction (XRD) spectrum of the glass ceramic samples were on a Phillips X’pert X-ray Diffractometer and the data were collected over the 2 range 10–80◦ at room temperature. The data then analysed by utilizing software X’pert HighScore. The field emission scanning electron microscopy (FESEM) was carried out on the samples coated with gold (Au) to observe the surface morphology of the obtained glass ceramics using Nova NanoSEM 30 Series
3728
N.A.S. Omar et al. / Optik 127 (2016) 3727–3729
under high vacuum. The photoluminescence excitation and emission spectra were required at room temperature by using Perkin Elmer LS 55 Fluorescence spectrometer at wavelength of 600 nm and 400 nm, respectively. 3. Results and discussion 3.1. X-ray diffraction analysis The XRD patterns of 1, 3, and 5 wt.% Eu3+ doped Zn2 SiO4 phosphor is shown in Fig. 1. All the diffraction peaks were matched very well with the standard values from the Joint Committee on Powder Diffractions Standards (JCPDS) data card number 37-1485, which can be assigned to willemite (␣-Zn2 SiO4 ). At the same time, a little amount of ZnO phase (JCPDS card No. 36-1451) together with AlNa(SiO4 ) phase (JCPDS card No. 02-0625) were also detected [14–16]. As can be seen from the XRD patterns, the intensity of diffraction peak was increased initially with the increasing of Eu doping from 1 to 3 wt.% and then were decreased on further addition of dopant, indicating a worse crystallinity due to lattice distortion [17].
Fig. 2 illustrates the FESEM image for 1, 3, and 5 wt.% Eu3+ doped Zn2 SiO4 phosphors sintered at 800 ◦ C. It is clearly seen that the surface morphology of particles were found in melted-like form and also having irregular shapes [18]. Thus, the results show that the doping process has a small effect on the morphological features as the sample decrease of the porosity after Eu3+ doping, thereby produce a bit larger ceramics [19]. 3.3. Photoluminescence properties The excitation and emission spectra of Zn2 SiO4 :xEu3+ (x = 1, 3, and 5 wt.%) are shown in Figs. 3 and 4. As seen in Fig. 3, the excitation spectra consist of five distinguished characteristic peaks centred at ∼400, 414, 460, 500, and 527 nm which are all ascribed to the intra-configurationally 4f–4f transitions of Eu3+ ions in this host lattice [20]. The most prominent peak is located at 400 nm which corresponds to the transitions 7 F0 → 5 L6 . In the following, this peak was used to record Eu3+ emission spectra (Fig. 4). The emission spectra under blue light (400 nm) excitation reveal five characteristic emission bands peaking at ∼527 nm, 575 nm, 600 nm, 653 nm, and 725 nm which is coming from 5 D1 → 7 F1 , 5D 5 5 5 7 7 7 7 0 → F1 , D0 → F2 , D0 → F3 , and D0 → F4 electronic transitions of Eu3+ ion, respectively. The intense emission peak located
♣ α-Willemite • Zinc Oxide
♣
Aluminium Sodium Silicate
♣
♣♣
♣♣
♣
♣♣ ♣
♣
450
500
550
Wavelength (nm) Fig. 3. Excitation spectrum of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
at around 600 nm (5 D0 → 7 F2 ) is attributed to the hypersensitive forced electric dipole transitions of Eu3+ which give the red colour in the luminescent signals [21,22]. With the increasing of dopant, the electric dipole transition (5 D0 → 7 F2 ) is much stronger than that of the emission peak at 575 nm (5 D0 → 7 F1 ) which is attributed to
C
♣♣
Intensity (a.u)
♣
• ♣
400
Intensity (a.u)
♣
Intensity (a.u)
Fig. 2. FESEM images of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
3.2. Morphological analysis
B
A
10
20
30
40
50
60
70
80
2θ (degree) Fig. 1. XRD patterns of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
500
550
600
650
700
750
Wavelength (nm) Fig. 4. Emission spectrum of Zn2 SiO4 :xEu3+ (x is (A) 1, (B) 3, (C) 5 wt.%).
N.A.S. Omar et al. / Optik 127 (2016) 3727–3729
magnetic dipole transitions [23]. It is also found that the emission intensity increases systematically with the increasing of Eu3+ ion concentration. 4. Conclusion In this work, Eu3+ (1, 3, and 5 wt.%) doped Zn2 SiO4 glass ceramics were successfully prepared by using the solid state method. The XRD pattern showed that 3 wt.% doping exhibited a good crystallization of willemite phase. Also, the addition of dopant has a small effect on the morphological features as the sample decrease of the porosity after Eu3+ doping. The emission peak of Zn2 SiO4 : xEu3+ was observed at 600 nm under the blue light excitation of 400 nm. Acknowledgements The authors gratefully acknowledge the financial support for this study from the Malaysian Ministry of Education (MOE), Ministry of Science, Technology and Innovation (MOSTI) and Universiti Putra Malaysia (UPM) through the Fundamental Research Grant Scheme (FRGS), Science Fund, and Putra Grant. The laboratory facilities provided by the Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, are also acknowledged. References [1] A. Patra, G.A. Baker, S.N. Baker, Synthesis and luminescence study of Eu3+ in Zn2 SiO4 nanocystals, Opt. Mater. 27 (2014) 15–20. [2] A.G. Joly, W. Chen, J. Zhang, S. Wang, Electronic energy relaxation and luminescence decay dynamics of Eu3+ in Zn2 SiO4 :Eu3+ phosphors, J. Lumin. 126 (2007) 491–496. ´ D.M. Petrovic, ´ M. Nikolic, ´ M.D. Dramicanin, ´ [3] Lj. Ðaˇcanin, S.R. Lukic, Judd–Ofelt analysis of luminescence emission from Zn2 SiO4 :Eu3+ nanoparticles obtained by a polymer-assisted sol–gel method, J. Phys. B: At. Mol. Opt. Phys. 406 (2011) 2319–2322. [4] H. Huang, B. Yan, In situ sol–gel composition of multicomponent hybrid precursor to hexagon-like Zn2 SiO4 :Tb3+ microcrystalline phosphors with different silicate sources, Appl. Surf. Sci. 252 (2006) 2967–2972. [5] H.X. Zhang, C.H. Kam, Y. Zhou, X.Q. Han, S. Buddhudu, Y.L. Lam, C.Y. Chan, Deposition and photoluminescence of sol–gel derived Tb3+ :Zn2 SiO4 films on SiO2 /Si, Thin Solid Films 370 (2000) 50–53. [6] V. Singh, T.K. Gundu Rao, Studies of defects in combustion synthesized europium-doped LiAl5 O8 red phosphors, J. Solid State Chem. 181 (2008) 1387–1392.
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