Optical and electron spin resonance spectroscopies have been used to investigate the thermal stability of lasers based onCr3+:LiSr0.8Ca0.2AlF6,a material in which the onset of critically inhibiting nonradiative decay at temperatures below 300 K might be expected based on results from otherCr3+-activated disordered gain media. The influence of disorder on theCr3+environment is shown to be very small inLiSr0.8Ca0.2AlF6so that the4T2→4A2fluorescence transition is not broadened relative to that inLiSrAlF6and the onset of significant nonradiative decay is also held above room temperature. ©1998 American Institute of Physics.