Red photoluminescence and purple color of naturally irradiated fluorite

Natural radiation-induced red fluorescence of fluorite consists of two broad bands at 750 and 635 nm with very short decay times of 20.3 and less than 5 ns, respectively. The first one is connected to an M center compensated by Na, while the second is connected to an M⁺ center, possibly formed as result of the M center’s destruction by UV irradiation. The optically active centers in naturally irradiated fluorite responsible for red luminescence and purple color are different from one another. The most probable reason for the purple color is colloidal calcium and not the M_Na center.