Phonon-Mediated Temperature Dependence of Er³⁺ Optical Transitions in Er₂O₃

Detailed understanding of the atomic level processes that determine the observed optical transitions in emerging materials is critical to the development of new platforms for classical and quantum networking. We report measurements of the temperature dependent Er³⁺ photoluminescence in single crystal Er₂O₃ thin films epitaxially grown on Si(111). Our focus is on transitions that involve the closely spaced Stark-split levels determined by the crystal field. Temperature dependent radiative intensities are compared to a model that includes these relevant Stark-split states, multiple single phonon-assisted excitations, and level population redistribution due to thermalization. The general approach, the first to treat the individual Stark-split states and employ material-specific single-phonon-assisted excitations, gives good agreement with the experiment. Sensitivity to the actual phonon spectrum is discussed. This study also suggests the tunability of the low temperature behavior of rare-earth ion emission as a function of excitation source.