Upconverting nanoparticles (UCNPs) compose a class of luminescent materials that utilize the unique wavelength-converting properties of lanthanide (Ln) ions for light-harvesting applications, photonics technologies, and biological imaging and sensing experiments. Recent advances in UCNP design have shed light on the properties of local color centers, both intrinsic and controllably induced, within these materials and their potential influence on UCNP photophysics. In this review, we describe fundamental studies of color centers in Ln-based materials, including research into their origins and their roles in observed photodarkening and photobrightening mechanisms. We place particular focus on the new functionalities that are enabled by harnessing the properties of color centers within Ln-doped nanocrystals, illustrated through applications in afterglow-based bioimaging, X-ray detection, all-inorganic nanocrystal photoswitching, and fully rewritable optical patterning and memory.

中文翻译：

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光暗化、光增亮以及色心在稀土基上转换纳米材料新兴应用中的作用

上转换纳米粒子 (UCNP) 构成一类发光材料，利用稀土 (Ln) 离子独特的波长转换特性，用于光收集应用、光子技术以及生物成像和传感实验。 UCNP 设计的最新进展揭示了这些材料中固有的和可控诱导的局部色心的特性及其对 UCNP 光物理学的潜在影响。在这篇综述中，我们描述了基于 Ln 的材料中色心的基础研究，包括对其起源及其在观察到的光暗化和光增亮机制中的作用的研究。我们特别关注通过利用 Ln 掺杂纳米晶体内色心的特性而实现的新功能，通过基于余辉的生物成像、X 射线检测、全无机纳米晶体光开关和完全可重写光学图案和记忆。