Effect of Tm3+ Concentration on Structure, Spectral Properties and Cross Relaxation of Tm:CaF2 Crystal

Through the investigation of spectral characteristics, the evolution of cluster proportions and the cross-relaxation process in Tm:CaF 2 crystals as a function of Tm doping concentration has been clarified. A quantitative model has been established to describe the relationship between these factors. At low concentrations (0.01-0.5 at.%), Tm ions rapidly form clusters with negligible cross-relaxation. As the concentration increases from 0.5 at.% to 2 at.%, the cluster ratio surpasses 90%, and its growth rate decelerates, while both the cross-relaxation rate and efficiency significantly increase. When the Tm concentration exceeds 2 at.%, the cluster ratio and cross-relaxation efficiency nearly reach 100% and remain stable. These findings provide valuable insights for the application of Tm:CaF 2 in high-energy pulsed laser systems.