Triplet–triplet annihilation upconversion based photoluminescence temperature sensing

Abstract Triplet–triplet annihilation upconversion (TTA-UC) is an anti-Stokes photoluminescence process that converts low-energy photons into higher-energy emissions, offering significant potential for applications ranging from solar energy harvesting to biomedical imaging and therapy. This perspective examines recent advances in TTA-UC for photoluminescence temperature sensing (PTS), with an emphasis on underlying mechanisms, emerging design principles, and future technological pathways. We systematically analyzed the fundamental principles of TTA-UC, temperature-response mechanisms, including thermally activated non-radiative decay and diffusion-controlled triplet energy transfer. We discussed the unique advantages of TTA-UC-based PTS, such as nonlinear temperature dependence, anti-Stokes shifted emission, microsecond-scale response times, and robustness in harsh environments. We evaluate TTA-UC-based PTS at both the bulk and nanoscale, highlighting its emerging applications in biomedical diagnostics and industrial monitoring. Finally, we outline future research directions to facilitate its practical development.