OPTICAL-PROPERTIES OF TRIVALENT TERBIUM DOPED CALCIUM FLUORAPATITE

The fluorescence of the Tb3+ ion in the apatite Ca10-2xNaxTbxF2(PO4)6 (0 less-than-or-equal-to x less-than-or-equal-to 2) is reported. The active ion is quasi exclusively located in the Cs site of the apatitic structure. Non radiative de-excitation from the 5D3 level to the 5D4 can be explained using cross-relaxation; the process is well described using the Inokuti and Hirayama model for a dipole-quadrupole interaction, leading to a Tb3+ critical concentration of 2.9% and to a critical distance of 1.21 nm. Moreover, at room temperature, phonons play a role in the 5D3 --> 5D4 relaxation, with a very weak probability.