Temperature dependence of the Cr3+ site axial distortion in LiSrAlF6 and LiSrGaF6 single crystals

The electron spin resonance (ESR) of Cr3+ in LiSrAlF6 (LiSAF:Cr) and LiSrGa F6 (LiSGaF:Cr) single crystals has been measured in the temperature range b etween 270 and 470 K. The external magnetic field orientation dependence of the spectra is described by a spin Hamiltonian of axial symmetry for both compounds. The value of the zero-field splitting axial parameter (D) for Li SGaF:Cr decreases from 6.60 x 10(-2) cm(-1) to 5.60 x 10(-2) cm(-1), while for LiSAF:Cr it increases from 1.30 x 10(-2) cm(-1) to 1.60 x 10(-2) cm(-1) for increasing temperature. The larger values of D obtained for LiSGaF:Cr show that the distortion of the octahedral Cr site is greater in this compo und, in agreement with x-ray diffraction results reported in the literature .