【JACS】北京大学严纯华、华南师范大学詹求强、北京大学孙聆东|三掺杂镧系离子实现近50%发射耗减：推动亚250纳米高分辨成像#

Figure 1. Scheme of the CR/ET-REED in lanthanide tridoped UCNPs under dual-wavelength excitation. (a) Upconversion process under single-wavelength excitation. (b) REED process under dual-wavelength excitation. The red arrow represents the re-excitation at the excited levels via ESA. (c) CR/ET-REED process under dual-wavelength excitation. Additional lanthanide ions, labeled as A3+ and B3+, were introduced to enable the ET and CR processes, respectively. Annotations of the arrows representing the transition processes are shown in the bottom panel.#

Figure 2. REED in Er3+ singly doped nanoparticles under dual-wavelength excitation. (a) Transmission electron microscopy (TEM) image of NaGdF4:0.5%Er nanoparticles. (b–d) TEM (b), high-resolution TEM (c), and high-angle annular dark field scanning TEM (d) images of NaGdF4:0.5%Er@NaYF4 nanoparticles. (e, f) Proposed upconversion (e) and REED (f) mechanisms of Er3+ under 795 nm single-wavelength excitation, and 795 and 1140 nm dual-wavelength excitation, respectively. Processes 5 and 6 are shown as dotted lines as they do not contribute to the green emission depletion. (g, h) Effect of the re-excitation wavelength on the upconversion emissions of NaGdF4:0.5%Er@NaYF4 nanoparticles. Upconversion emission spectra (g) and corresponding integrated green and red emission intensities (h) under 795 nm excitation (180 kW/cm2) and re-excitation at different wavelengths (400 kW/cm2). The reference spectrum in (g) was recorded under 795 nm excitation, and the corresponding intensity is shown as green and red dotted lines in (h). (i, j) Simulated rise curves (i) and corresponding fitted rise times (j) of the green and red emissions under 795 nm excitation, and 795 and 1140 nm dual-wavelength excitation. The rise time was defined as the time required to reach 95% stationary intensity.#

随后，团队引入Yb³⁺共掺杂，利用其能级结构与Er³⁺形成交叉弛豫通道，使耗减效率提升至约26.7%。进一步在Er³⁺–Yb³⁺–Ln³⁺（如Tb³⁺、Eu³⁺、Dy³⁺）三掺杂体系中，能量转移与交叉弛豫协同作用，使耗减效率达到48.5%，显著优于单掺杂与双掺杂体系。

Figure 3. CR-REED in Er3+–Yb3+ codoped UCNPs. (a) Proposed CR-REED mechanism for depleting the green emission of Er3+. (b) Green upconversion emission spectra of NaGdF4:0.5%Er,20%Yb@NaYF4 nanoparticles under 795 nm (180 kW/cm2) excitation, and 795 nm (180 kW/cm2) and 1140 nm (350 kW/cm2) dual-wavelength excitation. (c) Differential rate equation modeling results for the population of the green emissive levels of Er3+ under 795 nm excitation (ref), and 795 and 1140 nm dual-wavelength excitation with different CR1 routes (i–iv). (d) The simulated depletion efficiency with the four CR routes in (c). (e, f) Dependence of depletion efficiency of Er3+ green emission on the concentration of Yb3+ (e) and Er3+ (f) in NaGdF4,Yb@NaYF4 nanoparticles. In (e) and (f), the concentrations of Er3+ and Yb3+ were 0.5% and 20%, respectively.#

Figure 4. CR/ET-REED in Er3+–Yb3+–Ln3+ tridoped nanoparticles. (a, b) Dependence of the green emission depletion efficiency on Ln3+ content in NaGdF4:0.5%Er,20%Yb,x%Ln@NaYF4 nanoparticles, shown as a color map (a) and typical tridoped systems of Ln3+ being Ce3+, Eu3+, Tb3+, and Dy3+, respectively, which can improve the depletion efficiency (b). (c, d) Proposed CR/ET-REED mechanisms for the depletion of Er3+ green emission by tridoping with Yb3+/Ce3+ (c) and Yb3+/Tb3+ (d) under 1140 nm re-excitation. CR1 (i) was shown as the main CR1 pathway for clarity. (e, f) Green upconversion emission spectra of NaGdF4:0.5%Er,20%Yb,x%Ln@NaYF4 nanoparticles under 795 nm excitation (180 kW/cm2), and 795 nm (180 kW/cm2) and 1140 nm (350 kW/cm2) dual-wavelength excitation. x%Ln refers to 5%Ce (e) and 2% Tb (f), respectively. (g) TEM image of NaGdF4:0.5%Er,20%Yb,2%Tb@NaYF4 nanoparticles. The inset shows the size distribution. (h, i) Green upconversion emission spectra (h) and integrated intensity (i) of the tridoped nanoparticles under 795 nm excitation (180 kW/cm2) and 1140 nm re-excitation with different power densities.#

在成像实验中，三掺杂纳米颗粒在双波长激发下实现了分辨率从379 nm提升至249 nm，并在细胞骨架成像中进一步达到226 nm的分辨率，证明了该策略在超分辨显微成像中的潜力。

Figure 5. CR/ET-REED in lanthanide tridoped nanoparticles for high-resolution imaging. (a, b) Green upconversion emission (540–560 nm) imaging of single nanoparticles under 795 nm excitation (a) and 795 nm combined with 1140 nm dual-wavelength excitation (b). The green emission intensity distribution and corresponding Gaussian fitting of the selected nanoparticle are depicted in the right panel, and the fwhm is shown in the inset. (c, d) Subcellular imaging of the actin filaments with NaGdF4:0.5%Er,20%Yb,2%Tb@NaYF4 tridoped nanoparticles under 795 nm excitation (c) and overlay with the bright field (d). (e, f) Close-up imaging of the region of interest in (c) under 795 nm single-wavelength excitation (e) and 795 nm combined with 1140 nm dual-wavelength excitation (f). Right panels in (e, f) show PSF profiles and corresponding Gaussian fits along the dashed line crossing the actin filaments. Excitation intensity for 795 and 1140 nm is 180 kW/cm2 and 548 kW/cm2, respectively. Dimensions of images for single nanoparticle imaging (a, b) and subcellular imaging (c–f) are 512 × 512 and 640 × 640, respectively. Pixel dwell time is 200 μs for all of the images.#