The ability of materials to respond to stimuli with significant optical nonlinearity is crucial for technological advancement and innovation1,2,3. Although photon-avalanche upconversion nanomaterials with nonlinearities exceeding 60 have been developed, further enhancement remains challenging4,5,6. 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 33a''nm (about 1/32 of I'Exc) and 80a''nm (around 1/13 of I'Exc), respectively (where I'Exc is the excitation wavelength). Moreover, our research shows...
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