Growth, Physical Properties, Lattice Dynamics, and Defect Characteristics of Yb:LuGG Crystals

Abstract

Yb:Lu3Ga5O12 crystals have attracted considerable interest for tunable solid-state and ultrashort-pulse laser applications owing to their broad absorption and emission bandwidths. However, the high volatility of the Ga2O3 component during crystal growth readily causes deviations of the melt composition from stoichiometry and promotes the formation of crystal defects, thereby limiting the growth of high-quality crystals and the improvement of laser performance. In this work, Yb:LuGG single crystals were grown by the Czochralski method, and their local electronic structure, physical properties, lattice dynamics, and defect characteristics were systematically investigated through a combination of experimental characterization and first-principles calculations. The electron localization function (ELF) and charge-density difference analyses reveal that electrons are predominantly localized around O atoms, while the Yb/Lu/Ga−O bonds are primarily ionic with a certain degree of covalent character. Experimentally, the crystal exhibits a density of 7.75 g·cm−3, a Vickers hardness of 1140 kg·mm−2, a Mohs hardness of 7.05, and a room-temperature thermal conductivity of 4.40 W·m−1·K−1. No imaginary phonon frequencies are observed in the phonon dispersion curves, indicating good dynamical stability of the LuGG crystal. Moreover, the calculated infrared and Raman vibrational modes are in good agreement with the experimental results. Chemical etching experiments combined with surface-energy calculations demonstrate that the (100) plane possesses the highest stability, whereas the (111) plane is the most susceptible to chemical corrosion. Furthermore, positron annihilation lifetime spectroscopy, oxygen-vacancy formation-energy calculations, electron paramagnetic resonance spectroscopy, and optical transmission spectroscopy collectively confirm the presence of oxygen vacancies, while post-growth annealing effectively reduces oxygen-vacancy-related signals. These findings provide both theoretical insights and experimental evidence for understanding the structural stability, defect formation mechanisms, and performance optimization of Yb:LuGG crystals.