Yb3+ dopant concentration dependence in Yb:CaGdAlO4 bulk crystals

Abstract

Yb:CaGdAlO₄ (Yb:CALGO) single crystals having a series of Yb³⁺ concentrations (0.5, 1.7, 2.5, 5.0, 7.2, and 8.0 at%) were grown using the Czochralski method. X-ray powder diffraction (XRD), polarized absorption, fluorescence spectra, and Raman spectra were measured for the synthesized crystals to investigate the influence of the doping concentration of Yb³⁺ on the structure and spectral properties. The results indicate that Yb³⁺ doping concentrations within the tested range induce a negligible change in the structure but a significant change in the absorption and fluorescence features. Both polarized absorption and emission intensity in the π and σ-polarization increase with the increment of Yb³⁺ concentration. The fluorescence lifetimes, determined using the powder concentration dilution method, varied from 0.454 ms to 0.527 ms. Various spectral cross-sections of Yb:CALGO crystals were calculated and analyzed. Moreover, within the examined range, Yb³⁺ concentration exhibits negligible impact on the positions of the primary peaks observed in the Raman spectra. However, a notable intensity difference was observed at 311 cm⁻¹ in the Raman spectra measured along the a- and c-directions, which can be attributed to variations in the linkage of AlO₄⁵⁻ groups. This work provides a basis for the Yb:CALGO femtosecond laser experiments by optimizing the Yb³⁺ concentrations.