Point Defect and Proximal Interface Induced Modification of Er³⁺ Optical Transitions in Single Crystal Er₂O₃

Rare earth ions, such as Er³⁺, are receiving increased attention for modern telecommunication technologies, radiation damage and temperature sensing in nuclear technologies, and for emerging quantum information science applications. This is due largely to the fact that the 4f-4f electronic transitions in rare-earth ions are well-shielded from their environment by filled 5s and 5p orbitals which permits the 4f-4f electronic transitions to retain atomic-like character with low spectral diffusion. Our results demonstrate that the photophysical properties of solids incorporating Er₂O₃ depend on defect content. In particular, we characterize the influence of defects and proximal interfaces on the temperature dependance of photoluminescence (PL) emission intensity of Er³⁺ in molecular beam epitaxially grown single crystal Er₂O₃ thin films on silicon. The samples were subjected to 30 keV He⁺ ion beam irradiation with fluences from 1*10¹² atoms/cm² to 1*10¹⁵atoms/cm² to introduce ion irradiation damage up to 0.045 dpa (displacement per atom). Surprisingly, the defects induced by ion irradiation result in significant enhancements in PL intensity from specific Er³⁺ transitions. In addition, an unexpected non-linearity in erbium emission was observed as a function of decreasing thin film thickness. We discuss these effects in terms of the influence of defects on the crystal site symmetry of the host lattice and on the deviation from crystallinity near interfaces.