Inverse Determination of Radiation Absorption Coefficients of YAG Crystal and Melt Based on Melt–Crystal Interface Morphology

Internal radiation in yttrium aluminum garnet (YAG) crystal and melt significantly influences the morphology of the melt–crystal (m-c) interface during crystal growth. However, radiation absorption coefficients are difficult to measure directly under high-temperature conditions, and consequently, reliable radiation parameters suitable for numerical simulations of YAG crystal growth remain lacking. In this study, the effective radiative absorption coefficients of YAG crystal and melt were inversely determined by combining numerical simulations with crystal-growth and rapid pull-out experiments. A globally coupled multiphysics model for Czochralski growth of YAG crystals was developed using ANSYS Fluent 2024 R2, incorporating electromagnetic induction heating, PID-based heat-source control, and dynamic adjustment of the m-c interface through user-defined functions (UDFs) and user-defined scalars (UDSs). The effects of the absorption coefficients of YAG crystal and melt on the m-c interface morphology were systematically investigated. Comparison with experimental interface morphologies indicated an effective absorption coefficient of 20 m−1 for undoped YAG crystal and that the melt could reasonably be treated as an opaque medium. The experimentally obtained interface morphologies of undoped YAG, 1 at.% Nd:YAG, and 1.46 at.% Yb:YAG were highly consistent, indicating limited effects of Nd3+ and Yb3+ doping at the investigated concentrations. Thus, the same radiation parameters can reasonably be adopted for these lightly doped crystals.