Local structure regulation of multiple upconversion emission selectivity in highly doped lanthanide-based core–shell nanocrystals

Abstract

Optically active lanthanide-doped upconversion nanoparticles (UCNPs) typically 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 the 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 of 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 plentiful nanomaterial system choices for frontier applications such as anti-counterfeiting security, biosensors and biomedicine.