Local structure regulation of multiple upconversion emission selectivity in lanthanides highly-doped core-shell nanocrystals

Optically active lanthanide-doped upconversion nanoparticles (UCNPs) typical enhance their luminescence intensity by epitaxially growing an inert shell. However, related studies focusing on the regulation of their multiple upconversion emission selectivity remain limited. Herein, a novel regulation method is proposed to realize the selective regulation of Er3+ multicolor upconversion characteristic in Er3+ highly doped active core-inert shell UCNPs. This method involves intentionally reducing the amount of CF3COOLi precursor during the shell growth process, which decreases the orderliness and lattice density of local structure of the shell matrix and promotes the formation of F⁻ vacancy defects. These vacancy defects can provide additional non-radiative relaxation channels, facilitating the non-radiative energy transfer from high-energy excited state levels to the ground state, which leads to unique emission characteristics in the core-shell nanocrystals. Notably, the local structure-dependent multicolor modulation strategy is independent on the composition and thickness of the inert shell, further demonstrating the universality of the proposed regulation method. By using stoichiometric ratio deviations in the matrix materials to regulate the microscopic local structure, this approach provides a new strategy for the multicolor modulation of UCNPs, which can provide the plentiful nanomaterial system choices for frontier applications such as anti-counterfeiting security, biosensors and biomedicine.