Upconversion nanoparticles (UCNPs) are one kind of luminescence nanomaterials that convert low energy photons to high energy emissions. These nanomaterials have recently attracted enormous attention due to their unique photophysical properties, such as resistance to photobleaching and photoblinking, low background autofluorescence, and long luminescence lifetime. Owing to these unique advantages, UCNPs have been widely examined for biomedical applications, including biosensing, imaging, and theranostics. In this review, we have first summarized the mechanisms for three generally accepted upconversion luminescence processes, i.e., lanthanide (Ln) doped upconversion luminescence, dye-sensitized upconversion, and triplet–triplet annihilation upconversion, and then discussed recent advancements on the preparation, functionalization, and biomedical applications of each type of UCNPs. The review article finally concludes with our perspectives on UCNPs’ emerging and potential biomedical applications in the near future.

中文翻译：

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用于生物医学应用的上转换发光纳米材料的最新进展

上转换纳米粒子（UCNP）是一种将低能光子转换为高能发射的发光纳米材料。这些纳米材料由于其独特的光物理特性（例如，对光漂白和光闪烁的抵抗力，低背景自发荧光和长发光寿命）最近引起了极大的关注。由于这些独特的优势，UCNP已在生物医学应用（包括生物传感，成像和诊断学）中得到了广泛的检验。在这篇综述中，我们首先总结了三种普遍接受的上转换发光过程的机制，即镧系元素（Ln）掺杂了上转换发光，染料敏化上转换和三重态-三重态an灭上转换，然后讨论了每种类型UCNP的制备，功能化和生物医学应用方面的最新进展。这篇综述文章最后总结了我们对UCNPs在不久的将来新兴的和潜在的生物医学应用的观点。