Effect of pH on the optical and structural properties of HfO₂:Ln³⁺, synthesized by hydrothermal route

In this work, the influence of the chlorine ions in the optical and structural properties of hafnium oxide (HfO₂) doped with europium (Eu³⁺) and terbium (Tb³⁺) are reported. The synthesis was conducted by hydrothermal route at a temperature of 200 °C, with a reaction time of 80 min and a concentration of 3 mol% of both dopants, in relation to hafnium in solution. In order to study the influence of acidity on the kinetics of reaction, the pH of the precursor solution was varied in the range of pH=4 to pH=12. X-ray powder diffraction patterns showed that the materials crystallized better under alkaline conditions with pH=11, noting a better crystallinity in the material doped with Eu³⁺showed a better crystallinity that Tb³⁺ ions. The characteristic rhombohedral microstructure of HfO₂ in the monoclinic phase was observed in alkaline media. Photoluminescent spectra showed the characteristic peaks of the emissions for both Eu an Tb dopants, where the intensity of the luminescent emission increases by decreasing the concentration of chlorine ions. On the other hand, it was found that radiative life kinetics of the dopant is related to the kinetics of crystallization, and therefore, to the acidity of the precursor solution.