Tunable white light emission from hafnium oxide films co-doped with trivalent terbium and europium ions deposited by Pyrosol technique

In this paper, the photo and cathodoluminescent properties of HfO₂ films optically activated with different atomic concentrations of Tb³⁺ and Eu³⁺ ions, deposited by the Pyrosol technique, are reported. These films were deposited at temperatures from 400 to 600 °C, using chlorides as raw materials. The surface morphologies of all deposited films were rough and dense. X-ray diffraction analysis showed that the films deposited at 600 °C were polycrystalline exhibiting the HfO₂ monoclinic phase. The tuning by the means of the excitation wavelength generates photoluminescence spectra, for co-doped films, in several emissions from blue to yellow (including white light) due to the characteristic electronic transitions of Tb³⁺ (green), Eu³⁺(red) ions and the violet-blue emission associated to the host lattice (HfO₂). According to the chromaticity diagram, the best white light is reached for the sample S2 excited with 382 nm (x = 0.3343, y = 0.3406). The cathodoluminescence emission spectra for co-doped films showed emissions from green to red (including yellow, orange and other intermediate emissions). The averaged quantum efficiency values of the sample labeled as S2 resulted between 47 and 78% depending on the excitation wavelength. In addition, XPS, TEM, SEM and decay times were performed to characterize these films.