On the Temperature Behaviour of the Absorption of Additively Coloured Strontium Fluoride Crystals

An investigation is made of the density of the coloration centres as a function of the vapour pressure of the strontium metal used for coloration. In the temperature region between − 180 °C and + 300 °C the intensity of the two strongest coloration bands at 2.76 eV (449 nm) and 1.955 eV (634.5 nm) is shown to be temperature‐dependent. A model is proposed for the 2.76 eV band which is similar to that of colour centres. In the special case of the alkaline earth fluorides it is necessary to assume the existence of an anion vacancy, which has trapped an electron and is tetrahedrally surrounded by four nearest cations.