Spectroscopic investigations of calcium fluoroapatites doped with Bi3+

The spectral and dynamical properties of Bi3+ in the calcium fluorophosphates Ca5(PO4)3F and Ca5(VO4)3F are investigated at room and liquid nitrogen temperature. The data are interpreted at the light of recent semi-empirical models that allow calculating the energy of A-like (isolated Bi3+), D-like (metal-metal charge transfer) and pair-like transitions from the knowledge of the crystal structure of the host lattices. It is concluded that the attribution of the luminescence features to isolated Bi3+ ions is not always an obvious option and that the luminescence can also be very satisfactorily interpreted in terms of charge transfer processes, either within Bi3+- Bi3+ pairs in Ca5(PO4)3F-Bi3+ or within Bi3+- Bi3+ and Bi3+-V5+ pairs in the newly reported Ca5(VO4)3F -Bi3+.