Large plasmonic enhancements of upconversion luminescence (UCL) of lanthanide-doped materials are achieved usually by plasmon resonances at excitation wavelengths. Here, moderately high-Q plasmon resonance modes at emission wavelengths are used to control and enhance the UCLs of NaYF₄:Yb,Er nanoparticles on metal gratings. It is experimentally shown that, as Bloch-type plasmon resonance modes locate at/near the green- (≈540 nm) or red-emission (≈654 nm) wavelengths, the UCL is strongly enhanced (e.g., up to ≈117 times for the green and ≈272 times for the red), as well as large modifications of the green-to-red intensity ratios. The enhancement factors are comparable to or even much larger than those for plasmon resonances at excitation wavelengths reported in literatures. Importantly, it is disclosed that localized plasmon resonance modes in grooves of the metallic gratings, usually invisible in far-field characterization, can be excited by the emission dipoles (Er³⁺) in vicinity (i.e., in the near-field) to play an important role on UCL emissions. It is also inferred that the plasmon resonance modes at the emission wavelengths improve not only the Purcell factor for UCL emissions but also the energy transfer (Yb³⁺→Er³⁺) rates in excitation.

中文翻译：

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NaYF4:Yb,Er纳米粒子在金属光栅上的共振控制和上转换发光增强

镧系元素掺杂材料的上转换发光 (UCL) 的大等离子体增强通常通过激发波长的等离子体共振来实现。在这里，发射波长处的中等高Q等离子体共振模式用于控制和增强 NaYF _{4的 UCL}:Yb,Er 纳米粒子在金属光栅上。实验表明，由于 Bloch 型等离子体共振模式位于/接近绿色（≈540 nm）或红色发射（≈654 nm）波长，UCL 被强烈增强（例如，高达 ≈117 倍）绿色和红色的≈272倍），以及绿色与红色强度比的大修改。增强因子与文献中报道的激发波长处的等离子体共振的增强因子相当甚至更大。重要的是，公开了金属光栅凹槽中的局部等离子体共振模式，通常在远场表征中不可见，可以被发射偶极子（Er ³⁺) 在附近（即在近场）对 UCL 排放起重要作用。还推断发射波长处的等离子体共振模式不仅提高了UCL发射的珀塞尔因子，而且提高了激发中的能量转移(Yb ³⁺ →Er ³⁺ )速率。