An electron spin-resonance study of Cr3+in LiSrxCa1-xAlF6withx= 0, 0.5, 0.8, and 1

Electron spin-resonance (ESR) spectra of Cr 3+ ions in LiSr x Ca 1- x AlF 6 crystals with x = 0, 0.5, 0.8, and 1 have been measured at X-band microwave frequencies in the temperature range 1.3-300 K. The intense ESR lines from Cr 3+ ions in these crystals have been fitted to a trigonal spin Hamiltonian to determine values of the g -tensor ( g , g ) and zero-field splitting, 2 D . The principal g -values ( g g 1.974) are almost the same in all cases whereas 2 D increases sequentially for x = 0, 0.5, 0.8, and 1. The value of |2 D | for Cr 3+ :LiCaAlF 6 decreases gradually as the temperature is increased from 1.3 K to 300 K. Over this same temperature range the value of |2 D | for Cr 3+ :LiSrAlF 6 increases. The ESR spectra for Cr 3+ in LiSr 0.5 Ca 0.5 AlF 6 and LiSr 0.8 Ca 0.2 AlF 6 are inhomogeneously broadened by discrete centres with pseudo-trigonal symmetry, different configurations of which correspond to the random occupation of the second-nearest-neighbour cation sites by Ca 2+ and Sr 2+ ions.