Comparison of the photoluminescence properties of Eu2+, Mn2+ co-doped M5(PO4)3Cl (M = Ca, Sr, Ba)

Abstract

Eu2+ and Mn2+ singly doped or co-doped M5(PO4)3Cl (M=Ca, Sr and Ba) phosphors were synthesized by conventional solid state reactions and characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, PL decay curves, energy dispersive spectra (EDS) and Raman spectra. The results show that a better size match between the doped cation and the host cation allows a wider solid solution range (e.g. Ca2+/Mn2+) and a narrower emission band (e.g. Sr2+/Eu2+ and Ca2+/Mn2+). A lower phonon energy of the host (e.g. the Sr phase) reduces the non-radiation probability and enhances the PL efficiency. The PL performance of the Ba phase is exceptional possibly because of the large size difference between the doped cations and the host cations. The transfer efficiency (η) and the emission quantum efficiency (Q) were analyzed.In the studied phosphors, superficially Eu2+ efficiently transferred its absorbed energy to Mn2+ but the Q of the Mn2+ emission was not as high as expected. Two loss mechanisms are proposed: an “inverse bottleneck effect” and “charge transfer” between Eu2+ and Mn2+.