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Stimulated emission depletion (STED) microscopy is a powerful diffraction-unlimited technique for fluorescence imaging. Despite its rapid evolution, STED fundamentally suffers from high-intensity light illumination, sophisticated probe-defined laser schemes, and limited photon budget of the probes. Here, we demonstrate a versatile strategy, stimulated-emission induced excitation depletion (STExD), to deplete the emission of multi-chromatic probes using a single pair of low-power, near-infrared (NIR), continuous-wave (CW) lasers with fixed wavelengths. With the effect of cascade amplified depletion in lanthanide upconversion systems, we achieve emission inhibition for a wide range of emitters (e.g., Nd3+, Yb3+, Er3+, Ho3+, Pr3+, Eu3+, Tm3+, Gd3+, and Tb3+) by manipulating their common sensitizer, i.e., Nd3+ ions, using a 1064-nm laser. With NaYF4:Nd nanoparticles, we demonstrate an ultrahigh depletion efficiency of 99.3 ± 0.3% for the 450 nm emission with a low saturation intensity of 23.8 ± 0.4 kW cm−2. We further demonstrate nanoscopic imaging with a series of multi-chromatic nanoprobes with a lateral resolution down to 34 nm, two-color STExD imaging, and subcellular imaging of the immunolabelled actin filaments. The strategy expounded here promotes single wavelength-pair nanoscopy for multi-chromatic probes and for multi-color imaging under low-intensity-level NIR-II CW laser depletion.

Plant cell imaging is critical for agricultural production and plant pathology study. Advanced upconversion nanoparticles (UCNPs) are being developed as fluorescent probes for imaging cells and tissues in vivo and...

The key components in display, imaging, data communication, and photoelectric detection fields are low‐dimensional micro‐/nanomaterials with highly anisotropic optoelectronic properties manifesting polarized light. However, for anisotropic upconversion (UC) materials, obtaining tunable polarization characteristics remains a significant challenge. Herein, based on a detailed investigation of the crystal structure, local symmetry, and properties of rare‐earth ions (RE3+), the authors successfully realized a tunable UC light polarization characteristic (UCLPC) with dependence on excitation polarization using a series of RE3+ single‐ or co‐doped β‐NaYF4 microrods. By simulating the electron cloud distribution and bonding structure based on density functional theory calculations, it is shown that: i) Yb3+ with a unique electron cloud distribution adjusts the UCLPC of the activator via energy transfer processes; ii) co‐doping with RE3+ having a larger dipole polarizability improves the UCLPC of the activator by performing its electric field distribution toward anisotropy; and iii) increasing the activator concentration strengthens the UCLPC. By exploiting the unique UCLPC from different doping combinations, applications in optical storage, encryption, and anti‐counterfeiting are illustrated. Simultaneously, the findings obtained in this work will provide new and exciting fundamental insights into understanding the polarization properties of RE3+ in an anisotropic structure.

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