“…Especially, near‐infrared (NIR) light‐driven phosphors at nanoscale, such as upconversion nanoparticles (UCNPs) that capable of converting NIR stimulation into visible emission, present the advantages of deep‐tissue penetration, minimized background autoluminescence and photodamage, which have great potential applications in diagnostics, optical bio‐imaging, therapeutics and drug delivery, especially in subcutaneous and intracellular thermometry. [ 19–22 ] Generally, thermal reading at nanoscale could be remotely extracted through temperature‐dependent spectral parameters, such as emission intensity, lifetime, peak position, and band width. Among these approaches, thermal sensing based on absolute intensity from a single transition is greatly affected by the spectrum loss, fluctuations of excitation, and phosphor concentration.…”