Anomalous luminescent properties in ZnO and SrAl2O4 composites

Abstract

We have reported previously in a ZnO–SrAl₂O₄ composite synthesized through a solution combustion route that by dispersing 20 wt% of ZnO in the SrAl₂O₄ matrix and calcining at 700 °C, a stable hexagonal phase of SrAl₂O₄ at RT is established which is generally a high temperature phase of SrAl₂O₄ reported in the literature [Singh et al. 2014 Dalton Transactions]. By increasing the calcination temperature of the composite to 1200 °C, the hexagonal phase transforms into a stable, monoclinic phase of SrAl₂O₄. In addition, we have observed anomalous luminescent properties in these composites. In photoluminescence spectra, we observe near band edge emission and defect band emission (DBE) corresponding to ZnO without any signature of emission corresponding to SrAl₂O₄ in both the composites. The DBE peak is found to be stronger in the monoclinic phase than that observed in the hexagonal phase of SrAl₂O₄, indicating more defects in the former composite. Combining the excitation and emission properties, we propose a tentative model to illustrate the mechanism of excitation and emission processes involved in the composites. Thermoluminescence studies show a common glow peak at ∼323 °C in both composites and an additional glow peak at ∼158 °C in the composite with the monoclinic phase. An additional glow peak further confirms more defects in the monoclinic phase than in the hexagonal phase corroborating with PL and XRD results. With increasing γ-irradiation dose, the additional glow peak shows a linear dosimetric response. The composite with the monoclinic phase seems to be suitable for dosimetric application which will be confirmed after doing more measurements in future.