Ultrahigh optical nonlinearity of photon-avalanche nanocrystals and their super-resolution imaging performance under single-beam excitation. [Photo/en.xmu.edu.cn]
A joint research team, led by Professor Liang Liangliang of the Institute of Flexible Electronics (IFE, Future Technologies) at Xiamen University and Distinguished Professor Liu Xiaogang of the National University of Singapore, has achieved a major advance in photon-avalanche upconversion nanocrystals based on lanthanide-doped materials.
The research, titled "Optical nonlinearities in excess of 500 through sublattice reconstruction", was published in Nature.
The finding significantly enhances the performance ceiling of photon-avalanche materials, which are valued for their extreme sensitivity to weak optical stimuli and potential applications in super-resolution imaging, optical sensing, and multiphysics detection.
Photon avalanches are nonlinear optical processes in which emission intensity scales steeply with excitation power through a positive feedback loop. However, further improving nonlinearity has been constrained by the intrinsic properties of lanthanide ions, whose energy transitions depend heavily on the symmetry of their crystal environment.
To address this, the researchers developed a high-performance testing platform integrating automated laser power control, nanoscale positioning and time-resolved fluorescence detection. They then engineered the internal lattice of nanocrystals to induce crystal field distortions, enhancing energy transfer efficiency among ions.
By substituting lutetium ions for yttrium, the team introduced local structural distortions that accelerated cross-relaxation processes. This enabled nonlinearities exceeding 500 and reduced the response time to 8.5 milliseconds. In imaging tests, the material achieved lateral resolution of 33 nanometers and axial resolution of 80 nanometers, with high signal quality.
