Microscopic structure, thermophysical properties and crystal-growth simulations of Er:YAG melts

Abstract

Er³⁺-doped yttrium aluminium garnet (Er:YAG) is a vital gain medium for 2.9 μm lasers. Understanding its melt properties and structure is essential for elucidating crystal-growth mechanisms and guiding process design. We measured the density, viscosity, and surface tension of 20 at% Er:YAG melt using aerodynamic levitation, established temperature dependences, and validated the results through molecular dynamics (MD) simulations. Furthermore, we build MD models of 20 at% and 50 at% Er:YAG melts in LAMMPS and compute radial distribution functions and coordination numbers for Y, Er and Al. The results show that the mean bond length remains nearly constant at high temperature, whereas the local structure becomes progressively more disordered with increasing temperature, confirming temperature as a key control parameter for short-range order. We also find that Er³⁺ can readily substitute for Y³⁺ in the melt, which helps explain the observed temperature dependences of the macroscopic density and viscosity. Finally, using the measured density, viscosity and surface tension, we develop a two-dimensional axisymmetric steady-state model to systematically analyse how the rotation rate, pulling rate and insulation-structure parameters (thickness, height and aperture) affect the temperature field, flow field and the shape of the solid–liquid interface. Simulations indicate that using Er:YAG-specific parameters, rather than YAG data, leads to markedly different flow patterns and interface morphologies under varying growth conditions. This difference implies that substituting YAG parameters for Er:YAG can introduce substantial errors in growth simulations, underscoring the importance of measuring high-temperature properties of Er-doped YAG melts for accurate modelling of crystal growth. Under the optimised conditions suggested by the simulations, we grow a 20 at% Er:YAG single crystal with dimensions of 80 mm × 100 mm.