High efficient and broadband ∼3.5 μm emission of Er³⁺:YAG crystal

The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er³⁺ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er³⁺ concentration and ∼3.5 μm emission of Er³⁺:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 μm are slightly decreasing with the increase of Er³⁺ concentration. The trend of the emission properties in NIR and visible region with the Er³⁺ concentration was also discussed and compared. The results indicate that the highly doped Er³⁺ concentration is beneficial to realize the ∼3.5 µm laser output.