Photon avalanche nanomaterials: from spark to surge

Photon avalanche (PA) upconversion—once a rarely observed curiosity in bulk crystals—has rapidly emerged as one of the most powerful nonlinear optical phenomena achievable at the nanoscale. In a new Perspective published in PhotoniX, researchers outline how recent advances in lanthanide-doped nanomaterials have transformed PA from a fragile, traditionally low-temperature phenomenon into a robust platform capable of delivering ultrahigh-order nonlinearities at room temperature. These extreme responses arise from a self-reinforcing feedback loop of ground-state absorption, excited-state absorption and cross-relaxation, producing threshold-like emission and S-shaped power curves that far exceed the capabilities of conventional upconversion systems.

The article highlights how modern materials design—spanning host-lattice engineering, crystal-field modulation and precision control of core–shell interfaces—has unlocked unprecedented performance. By optimizing spatial ion distributions and stabilizing intermediate energy levels, researchers have achieved nonlinearities exceeding the 500th order alongside millisecond-scale response dynamics, marking a striking leap beyond traditional multiphoton processes. These advances not only deepen the fundamental understanding of PA photophysics but also establish a unified experimental framework for reliably identifying avalanche behavior across nanomaterial systems.

With this rapid surge in progress, PA nanocrystals are now poised to reshape applications in super-resolution imaging, ultrahigh-sensitivity sensing and emerging optical computing architectures. Their nonlinear response inherently compresses the optical point-spread function, enabling diffraction-breaking resolution on simple, single-beam microscopes. Meanwhile, their threshold behavior and memory-like dynamics open new possibilities for nanoscale optical switches, reservoirs and neuromorphic elements. As the Perspective argues, photon avalanche nanomaterials are transitioning from isolated sparks of discovery to rapidly accelerating surges—ones that promise to redefine how light is manipulated, amplified and harnessed in next-generation photonic technologies.