Photon upconversion that is characterized by high‐energy photon emission followed by lower‐energy excitation has been conventionally studied in bulk materials for several decades. This unique nonlinear luminescence process has become a subject of great attention since 2000 when upconverted emission was demonstrated in nanostructured crystals. In comparison with their bulk counterparts, nanostructured materials provide more room for optical fine‐tuning by allowing flexible compositional integration and structural engineering. Moreover, the high colloidal stability of nanoparticles coupled with high amenability to surface functionalization opens up a number of new applications for upconversion, especially in the fields of biology and life science. In this focus review, we discuss recent developments in upconversion materials through nanostructural design and review emerging biomedical applications that involve these nanostructured upconversion materials. We also attempt to highlight challenging problems of these nanomaterials that constrain further progress in utilizing upconversion processes.

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纳米结构材料的上转换：从光学调谐到生物医学应用

数十年来，传统上一直在散装材料中研究以高能光子发射，然后以低能激发为特征的光子上转换。自2000年纳米结构晶体中证明上转换发射以来，这种独特的非线性发光过程已成为备受关注的主题。与大量同类产品相比，纳米结构材料通过允许灵活的成分集成和结构工程设计，为光学微调提供了更大的空间。此外，纳米粒子的高胶体稳定性以及对表面功能化的高度适应性，为上转换打开了许多新的应用，特别是在生物学和生命科学领域。在这次重点回顾中，我们将通过纳米结构设计讨论上转换材料的最新发展，并回顾涉及这些纳米结构上转换材料的新兴生物医学应用。我们还试图强调这些纳米材料的挑战性问题，这些问题限制了上转换工艺的进一步发展。