Pressure-induced site swapping, luminescence quenching, and color tunability of Gd2Hf2O7:Eu3+ nanoparticles

Abstract High-pressure (HP) studies have been an active research area in fundamental physics and to meet demand of several technological applications. In this paper, we have explored the HP effect on optical properties of pyrochlore Gd2Hf2O7:5%Eu3+ (GHOE) nanoparticles (NPs). We have investigated several aspects of their optical properties under HP such as charge transfer transitions, emission dynamics, asymmetry ratio, excited state lifetime, and color coordinates. HP photoluminescence (PL) spectra indicate the irreversible and complete disappearance of charge transfer beyond ~5.4 GPa (up to 53 GPa) owing to the reduced charge density around O2− ion in the GHOE NPs. Elevated pressure induces peak broadening, evolution of emission from 5D1/5D2 states, and reduction of 5D0 → 7F2 red emission intensity due to enhanced defect density and cross relaxation. Moreover, there is systematic reduction in asymmetry ratio which suggests improving symmetry around Eu3+ ion and covalency reduction of Eu–O bond. PL lifetime spectroscopy suggests that a large fraction of Eu3+ ions is localized at Gd3+ site at lower pressure and the same changes to symmetric Hf4+ site with increasing pressure. Color coordinate value indicates their pressure induced color tunability in the red-orange-yellow domain. Hence, we demonstrated pressure induced site swapping, luminescence quenching, Eu–O covalency change, and color tunability of the GHOE NPs for high pressure research on optical materials.