Tracing Local Disorder in Near-Infrared-Upconverting Crystals of Li+-Doped Gd2O3 through the Gd(III)-O Bond Distance

Using atomic pair distribution function (PDF) analysis of high-energy synchrotron total scattering, the current study addresses how an imparted local disorder in near-infrared-upconverting (UC) crystals dictates the concerned bulk properties. Aiming to perturb the local crystal field symmetry around the activator ions, Li+ was incorporated in varying amounts within the UC crystals of Gd2O3/Yb3+/Ho3+. The respective photoluminescence (upconversion luminescence, UCL) intensities of the crystals got enhanced first and then diminished after a certain Li+ concentration. The phase of the crystal remained constant as the cubic Ia-3 space group in all the samples with no significant changes in average structures as obtained from the Rietveld refinement of synchrotron experiments. Results from extended X-ray absorption fine structure indicated some changes at the atomic level. A comparative analysis among the Li+-incorporated crystals was considered. Systematic PDF analysis revealed the appearance of local disorder, which was connected with the Gd(III)-O bond distances in some way. The extent of local disorder followed the variation trend of UCL intensities. When Gd1-O and Gd2-O approximately approached their respective shortest and longest limits among the Lit-incorporated crystals, the corresponding local disorder appeared to he maximum with the corresponding crystal showing the highest UCL intensity. The relative variation of Gd-O bond distances and hence the extent of local disorder was found to get manifested in the respective tensile lattice strains so generated. Through rationale and earlier published evidence, the study attempted to hypothesize that local disorder is fundamentally connected with the lattice strain in UC crystals at a significantly higher concentration of a symmetry perturbing agent.

Automated summary

This study investigates the effect of local disorder on the bulk properties of near-infrared-upconverting (UC) crystals. By analyzing the atomic pair distribution function (PDF) using high-energy synchrotron total scattering, the study found that the photoluminescence intensity of the crystals first increases and then decreases with increasing Li+ concentration. The local disorder is connected to the Gd(III)-O bond distances and is manifested in the tensile lattice strains. The results suggest that local disorder is fundamentally connected with lattice strain in UC crystals at high concentrations of symmetry perturbing agents.