Defect Centers in Calcium Fluorophosphate

Crystals of calcium fluorophosphate ${\mathrm{Ca}}_{10}$ ${\left(\mathrm{P}{\mathrm{O}}_4\right)}_6$ ${\mathrm{F}}_2$ have been grown from melts of various compositions. Optical and ESR measurements have been performed on samples before and after various treatments such as a uv irradiation and a thermal quench. Two kinds of defect centers have been detected: color centers produced by the irradiation, and more basic defects present in the samples before irradiation. The identity of two of these basic defects has been established and their role in the formation of the color centers has been deduced.