Color Centers in Additively Colored CaF₂ and BaF₂

Abstract

The electron spin resonance method is applied to the study of the structure of color centers in additively colored CaF2 and BaF2 crystals. Together with optical absorption measurements and bleaching experiments the results indicate that the α‐band in CaF2 and the 6600 Å band in BaF2 are due to an electron trapped in an F− vacancy. The hyperfine interactions between the unpaired electron and the surrounding nuclei are discussed and compared with the results obtained for F‐centers in alkali fluoride crystals. Furthermore, the optical bleaching experiments lead to probable models for other absorption bands in CaF2.

Determination of color centers in CaF2 crystals by multiple gamma-ray irradiations

“…The decrease in the 349, 409 and 478 nm bands is ascribed to this transformation. The 380 nm band in region II is quite close to the 375 nm band, which corresponds with the F center obtained by Arends [11] and the slight difference appears to be due to a perturbation of the center by impurities or imperfections in the various crystals.…”

Colour Centres in Alkaline Earth Fluorides

“…The principal object of the present work was, first, to examine the absorption spectra of X-irradiated calcium fluoride crystals of high purity prepared by different methods, and with raw materials from various sources, in the range 190 t o 750 nm, in order t o ascertain the influence of the more common trace impurities, including those of atmospheric origin, on the bands and, second, to attempt t o identify the F-bands of CaF,, SrF,, and BaF, with the aid of theoretical estimates of 1 s-2p transition energies of electrons trapped a t vacant fluorine sites. As the work was being completed Arends [9] published conclusive evidence of the existence of F-centers in calcium and barium fluoride crystals, obtained by electron spin resonance, the respective bands occurring a t about 375 and 660 nm in additively coloured Crystals. These results provided a welcome possibility for checking our calculations, and enabled us t o locate with fair confidence the F-centre in SrF,, for which as yet there are no ESR result,s.…”

Point defects in alkaline earth fluorides

“…measurements of Arends (12); endor measurements were later reported by Hayes and Stott. (13) Subsequently, e.p.r.…”