A Generalized Approach to Photon Avalanche Upconversion in Luminescent Nanocrystals

Photon avalanching nanoparticles (ANPs) exhibit extremely nonlinear upconverted emission valuable for subdiffraction imaging, nanoscale sensing, and optical computing. Avalanching has been demonstrated with Tm³⁺-, Pr³⁺-, or Nd³⁺-doped nanocrystals, but their emission is limited to a few wavelengths and materials. Here, we utilize Gd³⁺-assisted energy migration to tune the emission wavelengths of Tm³⁺-sensitized ANPs and generate highly nonlinear emission from Eu³⁺, Tb³⁺, Ho³⁺, and Er³⁺ ions. The upconversion intensities of these spectrally discrete ANPs scale with nonlinearity factor s = 10-17 under 1064 nm excitation at power densities as low as 7 kW cm^-2. This strategy for imprinting avalanche behavior on remote emitters can be extended to fluorophores adjacent to ANPs, as we demonstrate with CdS/CdSe/CdS core/shell/shell quantum dots. ANPs with rationally designed energy transfer networks provide the means to transform conventional linear emitters into a highly nonlinear ones, expanding the use of photon avalanching in biological, chemical, and photonic applications.