Effect of vacancy and activator concentrations on the luminescence of Sr1−1.5xTbx□0.5xWO4 and Tb3+/Li+ co-doped phosphors

Abstract

Tb3+-substituted SrWO4 Scheelite compounds are well-known green phosphors. Herein this work, we prepared three partial solid state solutions of Sr1−1.5xTbx□0.5xWO4 (□=vacancy, 0.01⩽x⩽0.24) and Sr0.64−yTb0.24Li2y□0.12−yWO4 (0⩽y⩽0.12) and Sr0.70−2zTb0.20+zLiz□0.10WO4 (0⩽z⩽0.10). Rietveld refinements on selected samples were performed to confirm the existence of A-site vacancies. In addition, the continuous variation of either Tb3+ or vacancy concentrations offers an opportunity to study the structure–property correlation. A decrease of Sr–O average distance and an elongation of W–O bond length were detected in Sr1-1.5xTbx□0.5xWO4, which result in a slight red-shifting of WO42− CT absorption band. The optimal concentration for green emission of Sr1−1.5xTbx□0.5xWO4 (0.01⩽x⩽0.24) was found to be 0.12. The occurrence of concentration quenching effect is not only due to the increase of the Tb3+ concentration, vacancies in the structure also play an important role. With Li+-co-doping, the emission shows a great enhancement not only due to the modification of the A-site coordination but also the diminishing of the A-site vacancy.