Synthesis, characterization and photoluminescence of high-entropy oxide (Y0.2Eu0.2Gd0.2La0.2Er0.2)2O3 nanopowders for lighting applications

The study focuses on the synthesis, structural characterization, and optical properties of high-entropy oxide (HEO) nanopowders (Y_0.2Eu_0.2Gd_0.2La_0.2Er_0.2)₂O₃. The nanopowders were synthesized using a co-precipitation method followed by thermal annealing at various temperatures. We demonstrate how annealing leads to an amorphous-to-crystalline transformation, increasing the optical band gap and improving luminescence properties, particularly in the UV-visible range. The photoluminescence behavior of Er³⁺ and Eu³⁺ ions reveals that increased crystallinity and removal of impurities enhance the intensity and quantum efficiency of emission. Judd-Ofelt theory, used to calculate the probabilities of radiative and nonradiative transitions, shows that thermal annealing improves the luminescence quantum efficiency up to 26.1%. The high probability of radiative transitions (1023.4 s^-1) underscores the promising opportunities for further research and development of HEOs for optoelectronic applications, including light-emitting devices and phosphors for solid-state lighting.