Co-Doping Effect of Mn and Eu on Luminescence in Strontiowhitlockite Phosphors.

A new series of Sr-based phosphates, SrMnEu(PO), 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-Ca(PO) (or β-TCP) structure. The concentration of Mn ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu to Eu 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 45-4 Eu and 4-4 Eu. The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn concentration due to quenching effect of Eu by the Mn levels. The temperature dependence of Eu photoluminescence in a SrMnEu(PO) host was investigated. The conditions for the reduction of Eu to Eu in air were discussed.