Structural and luminescent analysis of hafnium-doped yttrium oxide and yttrium-doped hafnium oxide powders and doped with trivalent europium and terbium ions

In this work, the structural and luminescent properties of Y₂O₃ powders doped with different concentrations of hafnium and the HfO₂ powders doped with different concentrations of yttrium are presented; these samples were also codoped with europium and terbium. The phosphors were obtained by means of the simple evaporation technique and were calcined at 800°C for 2 h. The excitation and emission spectra of the rare earth (RE) codoped samples are interpreted in terms of the characteristic intraelectronic energy levels of the trivalent RE. The emission peak with maximum intensity for the samples containing europium ions occurs at 611 nm when these ions are excited at 243, 245, and 247 nm wavelengths; this emission is related with the ⁵D₀ to ⁷F₂ transition. Terbium codoped samples give a maximum emission intensity at 542 nm when samples are excited with the following wavelengths λ_exc = 274, 271, and 273 nm, transition taking place between the ⁵D₄ and ⁷F₅ energy levels. The XRD results for similar samples were analyzed, and it was observed that they have a crystalline structure corresponding to a cubic system and a 21.93-nm grain size calculated by means of the Scherrer's formula and the Williamson-Hall method; SEM analyzes showed spherical agglomerates for HfO₂ samples, whereas Y₂O₃ showed porous laminar structures. Hafnium-doped yttrium oxide showed a combination of these structures as well as the Y₂O₃:Hf³⁺:Eu³⁺ codoped samples. The results for Y₂O₃:Hf³⁺, Tb³⁺ showed leaflet and lamellar structures not reported before for this kind of material. The CIE diagram shows tone shifts in the red and green region for emissions of RE-doped yttrium oxide and hafnium oxide powders.