Chemical state and optical response of erbium-doped silica: Role of doping level and thermal annealing

This study investigates the interplay between doping concentration and thermal treatment in determining the optical activation and chemical environment of erbium ions in sol–gel derived silica thin films. Erbium-doped silica samples with 3% and 6% Er 3 ⁺ were synthesized and annealed at 500 °C and 900 °C to evaluate their photoluminescence (PL) response and chemical structure. Photoluminescence spectroscopy revealed strong emission at ∼ 1533 nm exclusively in samples annealed at 900 °C, indicating thermally activated optical centers. Complementary X-ray photoelectron spectroscopy (XPS) provided mechanistic insight, showing a transition from hydroxyl-rich, weakly coordinated Er 3 ⁺ environments at 500 °C to well-integrated Er-O-Si and Er 2 Si 2 O 7 -like motifs at 900 °C. This shift was evidenced by increased Er 4d peak areas, sharpening of O 1 s and Si 2p core-level spectra, and reduced presence of non-radiative quenching centers. The results underscore the critical role of thermal processing in facilitating network densification, Er dispersion, and defect passivation. Together, the PL-XPS correlation provides a framework for tailoring rare-earth-doped silica films for integrated photonic applications, enabling efficient light emission at telecom wavelengths.