Direct evidence for transformation of multiple active crystallographic sites' symmetry in β-NaGdF4: Eu3+ nanocrystals

• Transformation model of multiple Eu3+ crystallographic sites symmetry is built.
• Model are confirmed for the first time experimentally and theoretically.
• Gain more insights into the optical behaviors of active Ln3+ ions in β-NaGdF4 NCs.
• Results provide an important guide for the role of certain luminescence properties.

β-NaGdF4 was doped with Eu3+ at different concentrations to investigate the transformation of multiple active Eu3+ crystallographic site symmetry. We first observed this transformation by studying the photoluminescence spectrum and built a corresponding structural transformation model. Through theoretical simulation and calculation, as well as study of luminescent properties, the structural transformation model was confirmed reasonably and different luminescent results for Eu3+ sites having different symmetry are obtained. Our results suggest that Ln3+ with different crystallographic site symmetry will exhibit different fluorescent properties in β-NaGdF4 nanocrystals, and this finding is of great significance for adjusting the β-NaGdF4 nanocrystal fluorescence characteristics for future applications.