Super-resolution imaging enabled by nonlinear optical response of upconversion nanoparticles

Exploration of the optical nonliniear response in different lanthanide emitters, including photon avalance (PA) luminescence and the emission saturation phenomenon has profound implications in plentiful frontier applications. In the past few years, our studies have reported several universal mechanisms to exhibit giant nonlinear responses in various avalanching emitters and generated record-breaking nonlinear responses up to the 60^th order in high-lying emitting levels for various emitters. By enabling full-spectrum PA luminescence ranging from the visible to near-infrared regions in various emitters, such as Tb³⁺, Eu³⁺, Dy³⁺, Nd³⁺,Tm³⁺, Er³⁺, Ho³⁺ and Yb³⁺, multi-color super-resolution imaging can be realized with a resolution of about 100 nm. Moreover, by further increasing the excitation intensity, the emissions become saturated. By replacing the excitation beam with a doughnut-shaped one, the emission saturation efffect tunes the inner dip of the detected PSF, enabled sub-40 nm super-resolution imaging in 200µm pig kidney slices. Studying these mechanisms opens up exciting avenues for new flexible and high-efficiency PA modulation in multilayer nanostructures, enabling the application of PA in more technologies, such as super-resolution imaging, lithography, and optical detection. In this report, we briefly introduced the mechanism and principles of nonlinear responses in upconversion nanoparticles and highlighted their novel applications in the field of super-resolution imaging.