Phase transformation and light emission in Er-doped Si-rich HfO₂ films prepared by magnetron sputtering

The impact of phase transformation on the emission properties of Er-doped Si-rich HfO₂ films obtained by RF magnetron sputtering has been investigated by means of the scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and photoluminescence techniques. It has been observed that thermal treatment of the films at 950 and 1100 °C governs a phase separation process. The formation of HfO₂ nanocrystals of the tetragonal phase together with the Si-quantum dots (QDs) occurs at 950 °C. Upon annealing at 1100 °C, the tetragonal SiO₂ and monoclinic HfO₂ nanocrystals appear. The appearance of bright emission in the visible-near-infrared spectral range, related to the optical transitions in the 4f intrashell energy levels of Er ions, has been detected. The investigation of the annealing effect on the luminescent properties has revealed that the enhancement of Er³⁺ emission occurs due to an effective energy transfer from Si-QDs toward the Er ions. The oxidation of Si-QDs at high temperature annealing (1100 °C) leads to a reduction in the intensity of the Er ion related emission. Since hafnia-based materials have high density and are very sensitive to high-energy excitation, the results offer multifunctional applications of doped hafnia films, such as the luminescent materials for traditional phosphors.