ABSTRACT Photon Avalanche (PA) is a unique, feedback‐driven upconversion process where the absorption of a single photon initiates cascaded excited‐state absorption and cross‐relaxation, leading to an exceptionally steep, threshold‐dependent emission rise. The realization of PA at the nanoscale has recently opened transformative opportunities in photonics, sensing, and optical computing. However, systematic exploitations of avalanching nanoparticles (ANPs) across diverse applications and rational design principles for next‐generation devices remain at an early stage. This Perspective examines the current status and future directions of research on ANPs, with emphasis on lanthanide‐doped fluoride systems. Initially, we analyze the PA mechanism and rate‐equation frameworks governing PA properties, including threshold intensity and cross‐relaxation efficiency. Next, we survey frontier applications, including super‐resolution imaging, nanothermometry, force sensing, optical logic gating, and neuromorphic computing. Ultimately, promising avenues for advancing ANP‐based technologies are outlined, spanning improved optical efficiency, chemical stability, homogeneity, and tunable threshold engineering. We hope this Perspective clarifies the foundations of PA at the nanoscale and provides a roadmap for exploiting avalanche mechanisms to unlock next‐generation functional platforms with enhanced performance and versatility.
Lee et al. (Sun,) studied this question.