ESR of x-ray induced centre in CaF2:Gd crystals

An ESR centre with orthorhombic symmetry was induced in CaF2:Gd crystals by X-ray irradiation after heat treatment at 9000C. The observed ESR spectrum has resolved shfs in particular crystal directions. Spin Hamiltonian analysis indicates that the ESR centre is a hole trapped at an oxygen substituted for a fluorine site and interacts mainly with two nearby fluorine ions located along the crystal [001] direction. The determined spin Hamiltonian parameters are gsub(xx) = 2.0036, gsub(yy)= 2.0159, gsub(zz) = 2.0306, Asub(xx) = 22.5, Asub(yy) = 5.6 and Asub(zz) = 5.6(G), respectively. A probable model is discussed by considering both the angular dependence of the ESR lines and the local charge neutrality around the ESR centre. (author)