Study on the effect of apatite structure on spectroscopic properties of bismuth activated alkaline earth metal chlorophosphate [M5(PO4)3Cl; M = Ca, Sr and Ba]

The luminescent properties of Bi activated M5(PO4)3Cl (M = Ca, Sr and Ba) prepared under the air and mild reducing conditions (5% H2 and 95% N2) were investigated. Results show that all samples present ultraviolet (UV) emissions of Bi3+ besides Ba5(PO4)3Cl prepared in reducing condition, which also shows broadband yellow–white and near infrared (NIR) luminescence attributed to univalent bismuth (Bi+). Emission data with the size available lattice sites of samples prepared in air suggests there are two types of Bi luminescent center, and each located in one of the two available M2+ lattice sites. In the case of Ba5(PO4)3Cl crystal, Bi3+ incorporated on Ba2+(1) sites can be reduced to Bi+ for reasons of charge compensation and size match of ionic radius.