ENDOR measurements on the Ce3+photochromic centre in CaF2

Abstract

¹⁹F ENDOR has enables us to characterise the photochromic centre of Ce³⁺ in CaF₂, confirming the tentative model of Anderson and Sabisky (1971), and Staebler and Schnatterly (1971). The centre definitely comprises a Ce³⁺ ion with as nearest neighbour an F'-centre, two electrons trapped at a fluorine ion vacancy. It has not been possible to account in detail for the measured transferred hyperfine interaction with the ¹⁹F ligand nuclei using simple molecular orbital models although its general magnitude corresponds to that expected. The hyperfine interaction with more distant nuclei indicates considerable displacement of the Ce³⁺-ion towards the F'-centre. A pseudonuclear Zeeman interaction, observed for ligands of Ce³⁺, is accounted for to somewhat better precision than the transferred hyperfine interaction. Electric field induced g-shifts have been measured and show no specially large contribution from the proximity of the F'-centre.