Photoluminescence of (ZnO)X-Z(SiO2)Y:(MnO)Z green phosphors prepared by direct thermal synthesis: The effect of ZnO/SiO2 ratio and Mn2+ concentration on luminescence

Abstract Green light emitting Zn 2 SiO 4 :Mn 2+ 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≤x≤0.05). The effect of both the Mn 2+ 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+ concentration x=0.03 (ZSMn3). The emission intensity of the ZSMn3 phosphor is comparable with the commercial Zn 2 SiO 4 :Mn 2+ 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+ 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.