Electron Spin Resonance of Point Defects in CaF2

Abstract

ESR of Nd³⁺ and U³⁺ in CaF₂ (Bleaney, Llewellyn, and Jones, 1956) provided the first confirmation of the hypothesis of Zintl and Udgård (1939) that charge compensation for a trivalent lanthanum ion is provided by an interstitial fluorine ion. In some cases this is in the nearest interstitial site, as shown by observation of magnetic dipole interaction between it and Ce³⁺ (Baker, Hayes, and O'Brien, 1960). In other cases the charge compensating defect is absent or so far away that cubic symmetry is preserved at the lanthanum site. The effects of x‐ray and ultraviolet irradiation at room and lower temperatures are being studied. Initial results show that Tm³⁺ ions can be converted readily to Tm²⁺, whose ESR spectrum has been measured (Hayes and Twidell, 1961). This has cubic symmetry, indicating that the Tm³⁺ ion is either accompanied by no defect or by a defect mobile at low temperatures. The spectra of Tm²⁺ and Yb³⁺ are compared. The work of Sierro (1961) on the hydrolysis of CaF₂ is discussed.