Enhancement of red emission in Ce3+, RE3+, Mn2+ codoped Ca5(BO3)3F phosphors: Luminescent properties and structural refinement

Abstract

Ce3+, Mn2+ codoped and Ce3+, RE3+, Mn2+ (RE3+ = Tb3+, La3+, Gd3+, Lu3+) codoped Ca5(BO3)3F phosphors have been synthesized by a high-temperature solid-state reaction. Crystal structure and site occupancy of the doped ions were determined by Rietveld refinement. Photoluminescence (PL) spectra as well as fluorescence lifetimes were investigated. Under the excitation of 360 nm, Ca5(BO3)3F:Ce3+, Mn2+ phosphors show a strong emission band at 392 nm and a very weak emission band at ∼630 nm, which belong to Ce3+ and Mn2+, respectively. The introduction of Tb3+ and even non-luminescent ions such as La3+, Gd3+ and Lu3+ to the Ce3+, Mn2+ codoped phosphors leads to the enhancement of Mn2+ emission. The analyses of fluorescence lifetimes suggest that there is energy transfer from Ce3+ and especially Tb3+ to Mn2+. However, Rietveld refinement results indicate that the introduction of RE3+ ions leads to the adjustment of Mn2+ ions from Ca(3) site to Ca(2) site, which is the key factor for the enhancement of Mn2+ emission. The crystal-site engineering is expected to provide a promising route to tune the luminescent properties of phosphors with more than one site for activators.