Co-Doping Effect of Mn 2+ and Eu 3+ on Luminescence in Strontiowhitlockite Phosphors.

A new series of Sr-based phosphates, Sr 9- x Mn x Eu(PO 4 ) 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-Ca 3 (PO 4 ) 2 (or β-TCP) structure. The concentration of Mn 2+ ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu 3+ to Eu 2+ 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 4 f 5 d -4 f Eu 2+ and 4 f -4 f Eu 3+ . The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn 2+ concentration due to quenching effect of Eu 3+ by the Mn 2+ levels. The temperature dependence of Eu 2+ photoluminescence in a Sr 9- x Mn x Eu(PO 4 ) 7 host was investigated. The conditions for the reduction of Eu 3+ to Eu 2+ in air were discussed.