Systematic Studies on RE₂Hf₂O₇:5%Eu³⁺ (RE = Y, La, Pr, Gd, Er, and Lu) Nanoparticles: Effects of the A-Site RE³⁺ Cation and Calcination on Structure and Photoluminescence

Abstract

A series of 5 mol % Eu 3+ -doped rare earth (RE) hafnium oxide RE 2 Hf 2 O 7 (RE = Y, La, Pr, Gd, Er, and Lu) nanoparticles (NPs) have been synthesized, calcinated, and systematically investigated using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and optically excited luminescence. Effects of the A-site RE 3+ cation and calcination on the crystal structure of the RE 2 Hf 2 O 7:5%Eu NPs were distinguished using XRD and Raman studies. Spectroscopic analysis showed that the La 2 Hf 2 O 7:5%Eu 3+ and Pr 2 Hf 2 O 7:5%Eu 3+ possessed ordered pyrochlore structures while the RE 2 Hf 2 O 7:5%Eu 3+ compositions (RE = Y, Er, and Lu) possessed disordered fluorite structure and were thermodynamically stable up to the highest calcination temperature employed in this study (1500 °C); however, a disordered–ordered transition observed in the Gd 2 Hf 2 O 7:5%Eu 3+ composition indicated that it was not thermodynamically stable. Detailed photoluminescence (PL) studies, including quantum yield and decay properties of each sample before and after calcination, were performed and correlated with their compositions and crystal structures. These results suggest that the A site RE 3+ cations and calcination of these RE 2 Hf 2 O 7:5%Eu NPs play important roles in their PL properties.