Paramagnetic resonance and electron nuclear double resonance of substitutional hydrogen atoms in CaF 2

Abstract

Recent infrared measurements have shown that hydrogen dissolves in CaF 2 as H - ions in fluorine sites (Elliott, Hayes, Jones, MacDonald & Sennett 1965). X-irradiation of CaF 2 : H crystals at room temperature produces paramagnetic hydrogen atoms in interstitial sites (Hall & Schumacher 1962). The present work shows that X-irradiation of CaF 2 : H crystals at 77°K produces hydrogen atoms in fluorine sites. These substitutional hydrogen atoms move into interstitial sites at 135°K giving rise to the e. p. r. spectrum observed by Hall & Schumacher in room temperature irradiated crystals. The present paper contains a detailed description of the e. p. r. and endor spectrum of the substitutional atoms in CaF 2 . It is found that the hyperfine interactions with second shell fluorines are smaller than with third and fourth shell fluorines and an explanation is suggested for this effect. Endor measurements of first shell fluorines show a resolved structure due to indirect fluorine-fluorine interactions. The endor measurements are of interest in connexion with the production and annealing mechanisms of the irradiation-induced defects.