Photoluminescence of (ZnO) X-Z (SiO 2 ) Y :(MnO) Z green phosphors prepared by direct thermal synthesis: The effect of ZnO/SiO 2 ratio and Mn 2 þ concentration on luminescence Peter Švančárek, Robert Klement n , Dušan Galusek Vitrum Laugaricio - Joint Glass Center of the IIC SAS, TnUAD, and FChPT STU, 911 50 Trenčín, Slovak Republic article info Article history: Received 4 July 2016 Received in revised form 15 July 2016 Accepted 26 July 2016 Keywords: Zn 2 SiO 4 Zinc orthosilicate Willemite Mn 2 þ -doped phosphors Green phosphor Photoluminescence Decay time Temperature dependent luminescence abstract Green light emitting Zn 2 SiO 4 :Mn 2 þ phosphors have been synthetised by the solid-state reaction in ambient atmosphere at 1300 °C for 2 h, with ZnO, SiO 2 and MnO 2 as the reagents. The ZnO/SiO 2 molar ratio varied from 2 to 0.5. The doping level was in a lower concentration range (0.01 rx r0.05). The effect of both the Mn 2 þ concentration and ZnO/SiO 2 molar ratio on luminescence intensity and decay was investigated in detail. The microstructure and phase composition of prepared phosphors were characterised by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). XRD results indicate that the pure α-Zn 2 SiO 4 phase with rhombohedral structure was obtained after heat treatment. The prepared phosphors exhibit a strong green emission centred at 525 nm from the 4 T 1 - 6 A 1 forbidden transition. The highest emission intensity was observed for phosphors with ZnO/SiO 2 molar ratio equal to 1.0, and the Mn 2 þ concentration x ¼0.03 (ZSMn3). The emission intensity of the ZSMn3 phosphor is comparable with the commercial Zn 2 SiO 4 :Mn 2 þ phosphor. The decay curves can be characterised by double exponential function. After fitting a fast component τ 1 ∼2 ms and a slow component τ 2 ∼10 ms were obtained. The decay times decrease significantly with increasing Mn 2 þ concentration. The decay time and luminescence mechanism depend on the excitation light wavelength. Temperature dependent luminescence of the ZSMn3 phosphor in the temperature range of 25–200 °C was studied. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. 1. Introduction Zinc silicate (Zn 2 SiO 4 ) is one of the most practical phosphors. It has been extensively studied due to its high luminescence effi- ciency, good colour purity, and excellent chemical and thermal stability [1,2]. Guests-ion-doped Zn 2 SiO 4 practical phosphors can emit blue green and red light depending on which ion is in- corporated (transition metal or rare earth ions) and what phase it belongs to (α-, β-Zn 2 SiO 4 ) [2–4]. Thus, Zn 2 SiO 4 has found a wide range of applications in fluorescent lamps, cathode ray tubes, medical imagining radiation detectors and plasma display panels (PDPs) [5]. The pure zinc silicate Zn 2 SiO 4 is known to exist in the form of various phases (polymorphs) crystallising in different space groups as pointed out by Syono et al. [6]. Among all polymorphs, the α-phase known also as willemite is the most common practical phase crystallising into rhombohedral lattice (R ̅ 3 space group). The structure is characterised by isolated [SiO 4 ] 4 À groups connected only by Zn 2 þ cations that occupy two non-equivalent distorted tetrahedral sites, Zn(1) and Zn(2), having only trivial (C 1 ) local symmetry. Manganese doped zinc silicate (Zn 2 SiO 4 :Mn 2 þ ) is an efficient green emitting phosphor with the advantage of having a highly saturated colour. The ways of synthesis of bulk Zn 2 SiO 4 :Mn 2 þ phosphors have been extensively studied. The synthetic methods range from conventional methods including solid-state reaction and flux method [7–10], through sol-gel methods [11–13], to hy- drothermal synthesis [14–16]. However, a post-treatment, at high temperature (from 1000 to 1400 °C) and under air or reducing atmosphere, is often required to obtain ordered willemite struc- ture even if the phosphor is prepared by sol-gel methods or hy- drothermal synthesis. The Mn 2 þ ions, due to the close ionic radii (0.74 Å for Zn 2 þ and 0.80 Å for Mn 2 þ ) occupy both Zn 2 þ sites in the structure of will- emite. The photoluminescence process of Zn 2 SiO 4 :Mn phosphor has been characterised by the transition of 3d 5 electrons in the manganese ions acting as activating centres in the willemite structure. In particular, the parity- and spin-forbidden transition, i.e. 4 T 1 ( 4 G)- 6 A 1 ( 6 S), from the lowest excited state to the ground Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ceramint Ceramics International http://dx.doi.org/10.1016/j.ceramint.2016.07.176 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding author. E-mail address: robert.klement@tnuni.sk (R. Klement). Please cite this article as: P. Švančárek, et al., Photoluminescence of (ZnO) X-Z (SiO 2 ) Y :(MnO) Z green phosphors prepared by direct thermal synthesis: The effect of ZnO/SiO 2 ratio and Mn 2 þ concentration..., Ceramics International (2016), http://dx.doi.org/10.1016/j. ceramint.2016.07.176i Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎