Li⁺ ions doping core–shell nanostructures: An approach to significantly enhance upconversion luminescence of lanthanide-doped nanocrystals

Highlights: • A new strategy was adopted to enhance luminescence intensity of UCNPs. • The mechanism for the luminescence intensity enhancement of UCNPs was discussed. • Significant enhancement of UC emission in β-NaGdF₄:Ln³⁺ nanocrystals was observed. - Abstract: Currently, enhancing luminescence efficiency of upconversion nanoparticles (UCNPs) has still been a challenging topic in despite of many efforts to improve UC luminescence. In this paper, a new strategy to enhance UC emission has been described based on coupling of Li⁺ ions doping with growth an inert shell. Significant enhancement of upconversion (UC) luminescence intensity of lanthanide-doped nanoparticles was observed under synergistic effect of internal adjustment and external approach. In addition, the mechanism for the luminescence enhancement of UCNPs has been discussed. Our results suggest that this UC enhancement strategy, proven here in NaGdF₄ nanoparticles, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays