Experimental and Simulation Insights into Local Structure and Luminescence Evolution in Eu3+-Doped Nanocrystals under High Pressure

Tremendous effort has been devoted to tailoring structure-correlated properties, especially for the luminescence of lanthanide nanocrystals (NCs). High pressure has been demonstrated as a decent way to tune the performance of lanthanide NCs; however, little attention has been paid to the local structure evolution accompanied by extreme compression and its effect on luminescence. Here, we tailor the local structure around lanthanide ions with pressure in beta-NaGdF4 NCs, in which Eu3+ ions were doped as optical probes for local structure for the sensitive electric dipole transition. As the pressure increases, the intensity ratio of the D-5(0) -> F-7(2) to D-5(0) -> F-7(1) transition decreases monotonically from 2.04 to 0.81, implying a higher local symmetry around Eu3+ ions from compression. In situ X-ray diffraction demonstrates that the sample maintains the hexagonal structure up to 33.5 GPa, and density functional theory calculations reveal the tendency of the local structure to vary under high pressure.