Photothermal lanthanide nanomaterials: From fundamentals to theranostic applications

Photothermal lanthanide nanomaterials with unique photophysical properties have been innovatively explored for diagnostics and non-invasive therapies, and hold great promise for precision theranostics. In this review, we start from the basic principles of excited-state dynamics and provide a thorough comprehension of the main pathways for photothermal conversion in lanthanide nanocrystals. Aspects influencing the photothermal effect such as lanthanide-doping concentration, particle size, and crystal structure have been fully discussed. Hybrid strategies for the design of efficient lanthanide-based photothermal agents, including dye sensitization to break the absorption limit and semiconductor combination to add cross-relaxation pathways, have also been summarized. Furthermore, we highlight the cutting-edge applications of photothermal lanthanide nanoplatforms with optical diagnosis and temperature feedback in photothermia-associated theranostics. Lastly, the current challenges and future efforts for clinical applications are proposed. This review is expected to offer a better understanding of photothermal mechanisms and inspire efforts for designing versatile lanthanide theranostic nanoplatforms.