On the Colour Centres and X‐Ray Luminescence of Calcium Fluoride Crystals

A study is made of differences in the colouration spectrum of calcium fluoride cyrstals obtained by X‐ray irradiation at different temperatures and by electrolysis. The changes occuring in the X‐ray luminescence spectrum due to the use of different irradiation temperatures are also considered. It is shown that the α‐ and β‐bands, usually only observed in additive and electrolytic colouration, can also be produced by X‐ray irradiation if the irradiation temperature is between 180 and 250°C. The formation of the α‐ band (the F‐band of this system) is difficult to detect at lower irradiation temperatures because of 1. the small number of free negative ion vacancies at these temperatures and 2. the low oscillator strength associated with this band. The changes observed in the X‐ray luminescence spectrum for different irradiation temperatures are explained and the associated electronic processes are discussed briefly.