Materials whose luminescence can be switched by optical stimulation drive technologies ranging from superresolution imaging^1,2,3,4, nanophotonics⁵, and optical data storage^6,7, to targeted pharmacology, optogenetics, and chemical reactivity⁸. These photoswitchable probes, including organic fluorophores and proteins, can be prone to photodegradation and often operate in the ultraviolet or visible spectral regions. Colloidal inorganic nanoparticles^6,9 can offer improved stability, but the ability to switch emission bidirectionally, particularly with near-infrared (NIR) light, has not, to our knowledge, been reported in such systems. Here, we present two-way, NIR photoswitching of avalanching nanoparticles (ANPs), showing full optical control of upconverted emission using phototriggers in the NIR-I and NIR-II spectral regions useful for subsurface imaging. Employing single-step photodarkening^10,11,12,13 and photobrightening^12,14,15,16, we demonstrate indefinite photoswitching of individual nanoparticles (more than 1,000 cycles over 7 h) in ambient or aqueous conditions without measurable photodegradation. Critical steps of the photoswitching mechanism are elucidated by modelling and by measuring the photon avalanche properties of single ANPs in both bright and dark states. Unlimited, reversible photoswitching of ANPs enables indefinitely rewritable two-dimensional and three-dimensional multilevel optical patterning of ANPs, as well as optical nanoscopy with sub-Å localization superresolution that allows us to distinguish individual ANPs within tightly packed clusters.

发光可以通过光刺激驱动技术切换的材料，范围从超分辨率成像^1,2,3,4、纳米光子学⁵和光学数据存储^6,7到靶向药理学、光遗传学和化学反应性⁸。这些光开关探针，包括有机荧光团和蛋白质，很容易发生光降解，并且通常在紫外或可见光谱区域工作。胶体无机纳米粒子^6,9可以提供更高的稳定性，但据我们所知，尚未在此类系统中报道过双向切换发射的能力，特别是近红外 (NIR) 光。在这里，我们提出了雪崩纳米颗粒 (ANP) 的双向近红外光开关，展示了使用 NIR-I 和 NIR-II 光谱区域中的光触发器对上转换发射的完全光学控制，可用于地下成像。采用单步光暗化^10,11,12,13和光增亮^12,14,15,16，我们证明了单个纳米粒子在环境或水条件下的无限光开关（7 小时内超过 1,000 个循环），没有可测量的光降解。通过建模和测量单个 ANP 在亮态和暗态下的光子雪崩特性，阐明了光开关机制的关键步骤。ANP 的无限、可逆光开关可以无限地重写 ANP 的二维和三维多级光学图案，以及具有亚 Å 定位超分辨率的光学纳米镜，使我们能够区分紧密堆积的簇内的单个 ANP。