Investigation of visible emission and luminescence center evolution in Pr–La:CaF2 single crystals for laser application

Abstract

A series of Pr,La:CaF₂ single crystals grown using the temperature gradient technique (TGT) method were presented systematically with a detailed spectroscopic investigation. The results indicate that the distinct Pr³⁺–La³⁺ cluster types have replaced the original Pr³⁺–Pr³⁺ clusters after introducing La³⁺ into the Pr:CaF₂ crystal, as demonstrated by density functional theory-based first principles calculation and spectral analysis. This cluster evolution has led to a drastic increase in the Pr³⁺ emission quantum efficiency as the La³⁺ concentration increases. Evaluation of the impacts of multiphonon relaxation and cross-relaxation processes on quantum yields also revealed that cross-relaxation processes persisted in the Pr, La co-doped samples, which led to not high quantum yields as expected. The incorporation of La³⁺ substantially manipulated the local structure of Pr ions in the CaF₂ crystal lattice. Low temperature absorption and selective-site spectroscopy, and time resolved emission spectroscopy were applied to investigate the local structure symmetries of Pr ions in the Pr³⁺,La³⁺:CaF₂ crystal. Despite a lower degree of discrepancy, two types of centers were observed in TRES, all of which showed cubic symmetry of these locations based on the cluster simulation.