Optical and EPR investigations of colour centres in calciumchlorapatite

Optical absorption measurements in combination with an EPR investigation of colour centres produced by X-rays in synthetic chlorapatite single crystals are presented. Models for both electron-excess and hole-excess centres are proposed and theoretical calculations of some of the hole-excess centres have been carried out. It turns out that the colour centres produced at temperatures higher than 77°K can be associated with oxygen impurities. Subtractive coloration at 5°K gives rise to the formation of F-centres.