Structural and spectroscopic characterizations in Pb2+-doped calcium hydroxyapatites

The luminescence properties of the Pb2+ ion in hydroxyapatites compounds Ca10−xPbx(PO4)6(OH)2 (0 < x < 10) are studied in a large range of temperature between 20 and 300 K. Calcium–lead apatite system shows a common apatitic structure and occurs as a continuous solid solution. Decay times of Pb2+ in this matrix have been measured and analyzed. According to the emission spectrum of Pb2+ two different cation sites have been identified in this apatite structure. As a consequence of the two different sites, two emission bands due to the 3P1 → 1S0 transition of the Pb2+ ion are observed within this structure. At room temperature and at low lead content x = 0.2 (2%), a blue emission has been observed and at low temperature an ultraviolet band appears, both originating from the same 3P1 level. For a higher lead content x > 5.0 (50%), concentration quenching occurs and these compounds do not present luminescence. To explain the strong dependence of the decay time τ on temperature, the assumption is made of the presence of the 3P0 metastable level. Correlations between luminescence and structure are discussed.