Vibronic relaxation processes of the FA center in RbCl:Li

► The vibronic relaxation process of FA centers in a laser active material. ► The explanation of the vibronic relaxation process of FA centers with the coexistence of Type I and Type II relaxations. ► Results of the time-resolved resonant secondary radiation (RSR) measurement. ► A new model of the de-excitation process in the FA centers.