Dielectric and Optical Absorption Measurements on CaF₂ and CaF₂:Y

Abstract

Abstract Crystals of oxygen free and oxygen contaminated CaF 2 were doped with yttrium. The dielectric loss of the unirradiated crystals was measured at 150 °C at different frequencies and a shift of the peak in the curves was found with varying concentration of yttrium. In oxygen free crystals the peak was displaced to higher frequencies whilst with oxygen contaminated crystals the shift was to lower frequencies. The optical absorption spectra were taken at room temperature before and after room temperature X‐irradiation. The uv optical absorption that exists in oxygen contaminated crystals even before X‐irradiation was found to decrease in yttrium doped crystals grown from oxygen contaminated material. It is proposed that the observed results could be explained on the assumption that one or more of the following associated defects are present in the crystals, namely: 1. an oxygen ion and fluorine ion vacancy, 2. an yttrium ion and an interstitial fluorine ion, 3. an yttrium ion and a substitutional oxygen ion. The shift of the dielectric loss peak to lower frequencies for yttrium doped oxygen contaminated crystals is correlated with the reduction of the uv optical absorption. It is suggested that possible explanation for this reduction is due to the formation of yttrium—oxygen dipoles. Thermal annealing of these crystals provides further confirmation of this suggestion.