Lanthanide-Doped KMgF₃ Upconversion Nanoparticles for Photon Avalanche Luminescence with Giant Nonlinearities

Abstract

Lanthanide (Ln³⁺)-doped photon avalanche (PA) upconversion nanoparticles (UCNPs) have great prospects in many advanced technologies; however, realizing efficient PA luminescence in Ln³⁺-doped UCNPs remains challenging due to the deleterious surface and lattice quenching effect. Herein, we report a unique strategy based on the pyrolysis of KHF₂ for the controlled synthesis of aliovalent Ln³⁺-doped KMgF₃ UCNPs, which can effectively protect Ln³⁺ from luminescence quenching by surface and internal OH^- defects and thereby boost upconversion luminescence. This enables us to realize efficient PA luminescence from Tm³⁺ at 802 nm in KMgF₃: Tm³⁺ UCNPs upon 1064 nm excitation, with a giant nonlinearity of ∼27, a PA response time of 281 ms, and an excitation threshold of 16.6 kW cm^-2. This work may open up a new avenue for exploring highly nonlinear PA luminescence through aliovalent Ln³⁺ doping and crystal lattice engineering toward diverse emerging applications.