Multimode responsive optical materials are garnering ever-increasing attention due to their diverse applications. This work showcases a film assembled with rare-earth-doped CaF₂ hollow nanospheres that exhibit water-vapor-triggered dual-mode optical responses. Upon exposure to flowing water vapor, the film rapidly (less than 1.5 s for a 7.7 μm thickness) transitions to a transparent state and simultaneously undergoes a sharp decrease in the photoluminescence intensity. Both of these changes fully reverse upon water evaporation, demonstrating an impressive reversibility over at least 200 cycles. The water-vapor-induced dual-mode responses are attributed to the altered incident light propagation path stemming from the similar refractive indices between CaF₂ and water, coupled with the water-induced energy loss of the rare-earth ions. The fabrication of encryption patterns displaying separate signals in multiple channels, as well as the demonstration of noncontact sensing for water vapor distribution, underscore the promising application potential of this dual-mode responsive system.

中文翻译：

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稀土掺杂空心纳米球中的水蒸气触发双模光学响应


由于应用多样化，多模响应光学材料越来越受到关注。这项工作展示了一种由稀土掺杂的 CaF₂ 空心纳米球组装而成的薄膜，该薄膜表现出水蒸气触发的双模光学响应。当暴露于流动的水蒸气中时，薄膜迅速（7.7 μm 厚度不到 1.5 秒）转变为透明状态，同时光致发光强度急剧降低。这两种变化在水分蒸发时完全逆转，在至少 200 次循环中表现出令人印象深刻的可逆性。水蒸气诱导的双模响应归因于 CaF₂ 和水之间相似的折射率以及水诱导的稀土离子能量损失引起的入射光传播路径的改变。加密模式的制造在多个通道中显示单独的信号，以及对水蒸气分布的非接触式传感的演示，强调了这种双模式响应系统的巨大应用潜力。