Co-Doping Effect of Mn2+ and Eu3+ on Luminescence in Strontiowhitlockite Phosphors

Abstract

A new series of Sr-based phosphates, Sr9−xMnxEu(PO4)7, were synthesized using the high-temperature solid-state method in air. It was found that these compounds have the same structure as strontiowhitlockite, which is a β-Ca3(PO4)2 (or β-TCP) structure. The concentration of Mn2+ ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu3+ to Eu2+ in air was observed and confirmed by photoluminescence (PL) and electron spin resonance (ESR) spectra measurements. The PL spectra recorded under 370 nm excitation showed transitions of both 4f5d–4f Eu2+ and 4f–4f Eu3+. The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn2+ concentration due to quenching effect of Eu3+ by the Mn2+ levels. The temperature dependence of Eu2+ photoluminescence in a Sr9−xMnxEu(PO4)7 host was investigated. The conditions for the reduction of Eu3+ to Eu2+ in air were discussed.