Surface-Sensitive Photon Avalanche Behavior Revealed by Single-Avalanching-Nanoparticle Imaging

Avalanching nanoparticles (ANPs) are a new class of lanthanide-based upconverting material demonstrating steep optical nonlinearities with the potential to advance applications ranging from subwavelength bioimaging to neuromorphic computing, nanothermometry, and pressure transduction. Here, we use single-nanocrystal imaging to uncover design-dependent heterogeneity in ANP threshold intensity (Ith). Quantitative comparisons between distributions of Ith and ANP shell properties reveal correlations between mean Ith values, histogram widths, and nanocrystal shell thickness. Evaluating avalanching behaviors using an established model of shell-dependent surface energy transfer shows that variations in shell thickness-and the resultant energy transfer through the shell to the surface and environment-are likely the primary contributor to ANP-to-ANP Ith heterogeneity. Further, nanocrystals with an similar to 6 nm average shell thickness show Ith heterogeneity beyond the extent expected from statistical measurements of shell size and variability using transmission electron microscopy (TEM). These results provide a principal guide for the design and application of ANPs to environmental sensing.