EPR of trivalent uranium in alkali-compensated SrF2

EPR of two new tetragonal centres of U3+ in alkali-compensated SrF2 is reported. The g-values are independent of the compensating ion (sodium or potassium) and are calculated for both centres I and II. They can be deduced from a unique set of cubic parameters if weak tetragonal distortions of opposite signs for the two cases are assumed. These parameters give a composition parameter x for the crystal-field potential of the virtual cubic centre and an orbital reduction factor ksub(j) in agreement with the values measured for cubic U3+ in CaF2. The centre II is attributed to a substitutional U3+ ion compensated by a substitutional monovalent ion at a (2, 0, 0) lattice site while the other centre is attributed to a distant compensated substitutional ion, slightly displaced towards a cube face. (author)