Fig. 1

Ce³⁺ doped rare-earth nanoparticles with enhanced NIR-IIb luminescence. a Schematic design of a NaYbF₄:Er,Ce@NaYF₄ core-shell nanoparticle (left) with corresponding large scale TEM image (upper right, scale bar = 200 nm) and HRTEM image (lower right, scale bar = 2 nm). b Simplified energy-level diagrams depicting the energy transfer between Yb³⁺, Er³⁺, and Ce³⁺ ions. c Schematic illustration of the proposed energy-transfer mechanisms in Er-RENPs with and without Ce³⁺ doping. d Upconversion and downconversion luminescence spectra of the Er-RENPs with 0 and 2% Ce³⁺ doping. e Schematic representation of Ce³⁺ doping concentration and corresponding upconversion and downconversion emission intensity of the Er-RENPs upon 980 nm excitation