The intrinsic limitations of mechanical and electrical thermometers have encouraged the development of non-contact optical thermometers on the micro- and nanoscales. Among the available methods, luminescence-based temperature sensors have received much attention in recent years. Several kinds of luminescent materials based on quantum dots, lanthanide phosphors,¹  organic dyes, polymer²  or metal–ligand complexes³  have been reported for temperature detection. Because of their fast response, high spatial and temporal resolution and biocompatibility, organic dye based luminescence thermometers are among the earliest and most used systems.^4–6 

According to previous research,^7–9  the luminescence of most organic compounds changes with temperature (T) via various mechanisms. There are usually more electrons of the molecules that are excited to non-emissive states at higher T, while the luminescence intensity decreased. However, only a few organic dyes can be used in thermometry for the following reasons: (1) their luminescence spectra should undergo a large change to provide good sensitivity; (2) the photostability of the organic dyes should be good enough to ensure precision; (3) the probes should not be toxic, especially if an in vivo use is intended; and (4) luminescence quantum yields should be high enough at different temperatures.^10–12