Thermal activation of upconversion luminescence in nanocrystals opens up new opportunities in biotechnology and nanophotonics. However, it remains a daunting challenge to achieve a smart control of luminescence behavior in the thermal field with remarkable enhancement and ultrahigh sensitivity. Moreover, the physical picture involved is also debatable. Here we report a novel mechanistic design to realize an ultrasensitive thermally activated upconversion in an erbium sublattice core–shell nanostructure. By enabling a thermosensitive property into the intermediate 4I11/2 level of Er3+ through an energy-migration-mediated surface interaction, the upconverted luminescence was markedly enhanced in the thermal field together with a striking thermochromic feature under 1530 nm irradiation. Importantly, the use of non thermally coupled red and green emissions contributes to the thermal sensitivity up to 5.27 K–1, 3 times higher than that obtained by using conventional thermally coupled green emissions. We further demonstrate that the controllable surface interaction is a general approach to the thermal enhancement of upconversion for a series of lanthanide-based nanomaterials. Our findings pave a new way for the development of smart luminescent materials toward emerging applications such as noncontact nanothermometry, information security, and anticounterfeiting.
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