Spectral properties of Er3+-doped CaGdAlO4 crystal for laser application around 1.55 μm

• Detailed spectral properties of the Er:CaGdAlO4 crystal have been investigated.
• Multi-phonon relaxation rate of Er3+ ions in the Er:CaGdAlO4 crystal is estimated.
• The quantum efficiency of the 4I13/2 level in the Er:CaGdAlO4 crystal is near 100%.

Room-temperature polarized spectral properties of the Er:CaGdAlO4 crystal are reported. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branch ratios. Room-temperature fluorescence lifetimes of the 4I13/2, 4I11/2, 4F9/2, and 4S3/2 multiplets for Er3+ ions were measured. Stimulated emission cross-sections of the 4I13/2 → 4I15/2 transition obtained by the Fuchtbauer–Ladenberg formula and the reciprocity method were compared. The results show that the Er:CaGdAlO4 crystal may be a potential gain medium for a low-threshold 1.55 μm laser.