Optical nonlinearities in excess of 500 through sublattice reconstruction

The ability of materials to respond to stimuli with significant optical nonlinearity is crucial for technological advancement and innovation^1-3. Although photon-avalanche upconversion nanomaterials with nonlinearities exceeding 60 have been developed, further enhancement remains challenging^4-6. Here we present a method to increase photon-avalanche nonlinearity beyond 500 by reconstructing the sublattice and extending the avalanche network. We demonstrate that lutetium substitution in the host material induces significant local crystal field distortions. These distortions strengthen cross-relaxation, the key process governing population accumulation. As a result, the optical nonlinearity is significantly amplified, enabling sub-diffraction imaging through single-beam scanning microscopy, achieving lateral and axial resolutions of 33 nm (about 1/32 of λ_Exc) and 80 nm (around 1/13 of λ_Exc), respectively (where λ_Exc is the excitation wavelength). Moreover, our research shows regional differentiation within photon-avalanche nanocrystals, in which photon-avalanche performance varies across different regions at the single-nanoparticle level. This effect, coupled with extreme optical nonlinearity, enables visualization of nanoemitters at resolutions beyond their physical size using simple instrumentation. These advancements open new possibilities for super-resolution imaging, ultra-sensitive sensing, on-chip optical switching and infrared quantum counting.