Lanthanide-Doped KMgF 3 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 KHF 2 for the controlled synthesis of aliovalent Ln 3+ -doped KMgF 3 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 Tm 3+ at 802 nm in KMgF 3 : Tm 3+ 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 Ln 3+ doping and crystal lattice engineering toward diverse emerging applications.