Effect of carbonates on hydroxyapatite self-activated photoluminescence response

The effect of carbonate impurities in the photoluminescence (PL) properties of hydroxyapatite has been studied. Different hydroxyapatite samples were synthesized by chemical precipitation with some differences in the purity of the precursors or the final neutralization treatment. All the materials were calcined in the temperature range of 200-800 °C. Calcination treatments in the range of 400-450 °C resulted in intense and broad luminescence spectra. Especially high PL intensity was obtained in samples HaB which was neutralized with phosphoric acid and in HaD a carbonated apatite. The band gap of these samples was in the range of 3.1-3.96 eV. The materials were characterized by Fourier Transformed Infrared spectroscopy, scanning and transmission electron microscopy, differential scanning calorimetry and x-ray diffraction. The time resolved luminescence decay was in the range from 500 to 980 ms in samples HaB, for calcination temperatures from 400 to 500 °C. The PL properties of these non-toxic materials made them very promising for new optical applications.