Understanding the structure-property relationship and optimizing properties of phosphors for use in lighting and scintillation fields is an important materials challenge. In this work, we investigated the effects of the pH value of the coprecipitating solution adjusted by the concentration of NHOH(aq) on the structure and optical properties of the obtained LaHfO nanoparticles (NPs). The obtained NPs stabilize in the ideal pyrochlore structure, but the extent of ordering increased with an increase in the pH value used. The NPs prepared at pH = 12.1 displayed the best optical performance owing to the balance of the crystallinity, agglomeration, and surface defects. On the basis of density functional theory (DFT) calculations, the origin of violet-blue emission in undoped LaHfO NPs was attributed to defect states in the electronic band gap arising due to oxygen defects. For the LaHfO:Eu NPs, the Eu dopants possess low symmetry and their occupancy is more favorable at the LaO site. DFT calculations further justify the complete host-to-dopant energy transfer and origin of the most intense red emission observed experimentally. Understanding the interplay of the experimental and theoretical results thus is a very useful general approach for improving the efficiency of luminescent materials.

Doping induced phase transformation and speciation of the uranium ions in La2Hf2O7 nanoparticles as nuclear waste host were investigated.

High temperature annealed La2Hf2O7:Eu3+ nanoparticles favor tunneling of Eu3+ to symmetric sites showing orange emission, whereas low temperature annealed samples favor red emission.