Dual-emission flexible composite films for RGB-based visual optical thermometry

Optical thermometric materials have emerged as promising candidates for non-contact temperature monitoring, intelligent sensing systems, and flexible optoelectronic devices. Nevertheless, most phosphor-based optical thermometers are currently restricted to powder form samples and spectrometer-dependent signal readout, which severely limits their capability for intuitive, convenient, and visual temperature detection. Herein, a series of Bi 3+ /Sm 3+ co-doped Sr 2 Ga 2 SiO 7 (SGSO) phosphors were successfully synthesized, and dual-emission flexible composite films were further fabricated to realize fluorescence intensity ratio (FIR)-based thermometry and RGB-assisted visual temperature sensing. Benefiting from the discrepant thermal response characteristics of Bi 3+ and Sm 3+ luminescence centers, the resultant phosphor exhibits excellent FIR thermometric performance. Notably, the flexible composite film displays a distinct temperature-dependent luminescence color variation, transitioning from bluish-purple to reddish-purple as the temperature increases. By extracting RGB information from digital images, quantitative correlations between temperature and the R/G as well as the R/B ratios were established. The R/G sensing parameter achieves a maximum relative sensitivity of 0.962% K −1 , enabling accurate and reliable temperature prediction with low detection errors. Moreover, the composite film possesses superior cycling stability of RGB ratio responses after repeated thermal cycling and mechanical bending tests. This work provides a feasible and effective strategy for the construction of flexible visual optical thermometric devices by utilizing dual-emission phosphors, which simplifies the temperature readout process and promotes the practical application of phosphor-based thermometers.