Quality of the rare earth aluminum borate crystals for laser applications, probed by high-resolution spectroscopy of the Yb3+ ion

► Spectroscopic method was applied to analyze impurities in RAl3(BO3)4:Yb3+ compounds. ► The crystals with the lowest concentration of Mo have the highest UV transparency. ► Recommendations are given for the improvement of the growth technique. A comparative study was performed of the low-temperature high-resolution absorption spectra of the Yb3+ probe in R1−xYbxAl3(BO3)4 (R=Y, Tm, Lu) crystals grown by flux technique independently in four different laboratories using different solvents. We show that the incorporation of solvent components into the crystal in the course of crystallization gives rise to spectral satellites of the Yb3+ 0(2F7/2)→0′(2F5/2) absorption lines and assign particular satellites to the Yb3+ centers near the bismuth and molybdenum impurities (which decrease the transparency of YAB in the UV spectral range). We suggest this spectroscopic method for a rapid analysis of the quality of UV laser crystals and for improvement of growth technologies.