ABSTRACT
The development of super-resolution fluorescence microscopy is very essential for understanding the physical and biological fundamentals at nanometer scale. However, to date most super-resolution modalities require either complicated/costly purpose-built systems such as multiple-beam architectures or complex post-processing procedures with intrinsic artifacts. Achieving three-dimensional (3D) or multi-channel sub-diffraction microscopic imaging using a simple method remains a challenging and struggling task. Herein, we proposed 3D highly-nonlinear super-resolution microscopy using a single-beam excitation strategy, and the microscopy principle was modelled and studied based on the ultrahigh nonlinearity enabled by photon avalanches. According to the simulation, the point spread function of highly nonlinear microscopy is switchable among different modes and can shrink three-dimensionally to sub-diffraction scale at the photon avalanche mode. Experimentally, we demonstrated 3D optical nanoscopy assisted with huge optical nonlinearities in a simple laser scanning configuration, achieving a lateral resolution down to 58 nm (λ/14) and an axial resolution down to 185 nm (λ/5) with one single beam of low-power, continuous-wave, near-infrared laser. We further extended the photon avalanche effect to many other emitters to develop multi-color photon avalanching nanoprobes based on migrating photon avalanche mechanism, which enables us to implement single-beam dual-color sub-diffraction super-resolution microscopic imaging.
ABSTRACT
Photon avalanche has received continuous attention owing to its superior nonlinear dynamics and promising advanced applications. However, its impact is limited due to the intrinsic energy levels as well as the harsh requirements for the composites and sizes of doped materials. Here, with a universal mechanism named tandem photon avalanche (TPA), giant optical nonlinear response up to 41st-order in erbium ions, one of the most important lanthanide emitters, has been achieved on the nanoscale through interfacial energy transfer process. After capturing energy directly from the avalanched energy state 3 H4 of Tm3+ (800-nm emission), erbium ions also exhibit bright green and red PA emissions with intensities comparable to that of Tm3+ at a low excitation threshold (7.1 kWcm-2 ). Using the same strategy, effective PA looping cycles are successfully activated in Ce3+ and Ho3+ . Additionally, Yb3+ -mediated networks are constructed to further propagate PA effects to lowly-doped Tm3+ , enabling 475-nm PA emission. The newly proposed TPA strategy provides a facile route for generating photon avalanche not only from erbium ions but also from various emitters in multilayered core-shell nanoparticles.
