Polarized Luminescence of X‐Irradiated CaF₂:Y and SrF₂:Y Crystals and the Structure their Luminescence Centres

Y‐doped CaF 2 and SrF 2 crystals coloured subtractively by X‐rays at room temperature exhibit a broad luminescence band at 86°K in the near infrared if they are irradiated with light of the three long‐wavelength bands of the four‐band absorption spectrum. The peak of luminescence lies at 1.32 μm for CaF 2 : Y and 1.46 μm for SrF 2 :Y. The luminescence is partially polarized, the luminescence centres are oriented along the threefold axes ([111]‐directions). The results are shown to be in contradiction to earlier conceptions of the origin of the atomic centres in Y‐doped alkaline earth fluoride crystals. They are however compatible with a new model consisting of an electron trapped in a fluorine vacancy which is disturbed by a nearest neighbour Y 3+ ‐ion.