Mechanisms behind blue, green, and red photoluminescence emissions in CaWO4 and CaMoO4 powders

Abstract

A combined experimental and theoretical study was conducted to analyze the photoluminescence (PL) properties of ordered and disordered $\mathrm{Ca}\mathrm{W}{\mathrm{O}}_4$ (CW) and $\mathrm{Ca}\mathrm{Mo}{\mathrm{O}}_4$ (CM) powders. Two mechanisms were found to be responsible for photoluminescence emission in CW and CM powders. The first one, in the disordered powders, was caused by oxygen complex vacancies $[M{\mathrm{O}}_3\bullet V_{\mathrm{O}}^{\mathrm{x}}]$ , $[M{\mathrm{O}}_3\bullet {\mathrm{V}}_{\mathrm{O}}^{•}]$ and $[M{\mathrm{O}}_3\bullet V_{\mathrm{O}}^{••}]$ , where $M=\mathrm{W}$ or Mo, which leads to additional levels in the band gap. The second mechanism, in ordered powders, was caused by an intrinsic slight distortion of the $\left[\mathrm{W}{\mathrm{O}}_4\right]$ or $\left[\mathrm{Mo}{\mathrm{O}}_4\right]$ tetrahedral in the short range.