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

A series of 5 mol % Eu3+-doped rare earth (RE) hafnium oxide RE2Hf2O7 (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 RE3+ cation and calcination on the crystal structure of the RE2Hf2O7:5%Eu NPs were distinguished using XRD and Raman studies. Spectroscopic analysis showed that the La2Hf2O7:5%Eu3+ and Pr2Hf2O7:5%Eu3+ possessed ordered pyrochlore structures while the RE2Hf2O7:5%Eu3+ 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 Gd2Hf2O7:5%Eu3+ composition indicated that it was not thermodynamically stable. Detailed photoluminescence (...