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

Lanthanide (Ln(3+))-doped photon avalanche (PA) upconversion nanoparticles (UCNPs) have great prospects in many advanced technologies; however, realizing efficient PA luminescence in Ln(3+)-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 Ln(3+)-doped KMgF3 UCNPs, which can effectively protect Ln(3+) 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 similar to 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 Ln(3+) doping and crystal lattice engineering toward diverse emerging applications.