Thermally induced evolution of optical and structural properties of Er2O3 films grown on Si substrates by thermal atomic layer deposition

•Er2O3 films were grown by water-assisted atomic layer deposition.•Cubic Er2O3 phase was detected in as-deposited and annealed at TA < 900 °C films.•Annealing at TA = 900–1100 °C stimulates Si diffusion in film volume.•Er silicate phase (Er2SiO5) were found on film surface at TA = 1100 °C.•Host defects (like oxygen vacancies) and Er3+ ions contribute to PL emission.