Photon-avalanche (PA) excitation of trivalent lanthanide ions is a fascinating mechanism in which the material is initially transparent to the exciting radiation. Through the participation of phonons from the host medium, some ions are promoted to an excited state. A series of cross-relaxation and excited-state absorption can double the number of excited ions with each iteration, leading to intense emissions. Although first reported many years ago, PA has since been utilized to generate upconversion emissions. Here, we leverage the richness of Nd³⁺ electronic structure to demonstrate, for the first time, downshifting emissions under PA excitation. As a proof-of-concept, PA-like excitation at 1064 nm of Nd³⁺ in NdAl₃(BO₃)₄ particle powders is demonstrated, resulting in emissions in the range of 1200–1800 nm, corresponding to Nd³⁺ electronic transitions. Recently, unprecedented applications of PA have been reported in super-resolution imaging, thermal sensors, and optical transistors based on light wavelengths below 1000 nm. Our findings extend the wavelength range of PA, opening up new possibilities for its application.

中文翻译：

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类似光子雪崩激发的近红外下移发射

三价镧系元素离子的光子雪崩 （PA） 激发是一种迷人的机制，其中材料最初对激发辐射是透明的。通过来自宿主介质的声子的参与，一些离子被提升到激发态。一系列交叉弛豫和激发态吸收会使每次迭代的激发离子数量增加一倍，从而导致强烈的发射。虽然 PA 在多年前首次报道，但此后一直被用于产生上变频发射。在这里，我们利用丰富的 Nd³⁺ 电子结构，首次展示了在 PA 激励下降低发射。作为概念验证，证明了 NdAl₃（BO₃）₄ 颗粒粉末中 Nd³⁺ 在 1064 nm 处的 PA 样激发，导致发射波长在 1200–1800 nm 范围内，对应于 Nd³⁺ 电子跃迁。最近，据报道，PA 在超分辨率成像、热传感器和基于 1000 nm 以下光波长的光学晶体管方面的应用前所未有。我们的研究结果扩展了 PA 的波长范围，为其应用开辟了新的可能性。