Ratiometric optical thermometer based on the use of manganese(II)-doped Cs3Cu2I5 thermochromic and fluorescent halides.

The inconsistent thermal quenching performance of manganese(II)-doped Cs3Cu2I5 microparticles is exploited in a highly sensitive noninvasive optical thermometer. The ratio of the emissions of Cu(II) and Mn(II) ions in the microparticles is highly temperature dependent in the range from 298 to 498 K. The best absolute and relative sensitivities are 0.547 K-1 and 0.525% K-1, respectively. The emission spectrum, under 300-nm photoexcitation, has emission peaks at 448 and 556 nm. This is the result of energy transfer between the Cu(II) and Mn(II) ions whose efficiency can reach up to 57% when the Mn(II) ion concentration is 2 mol%. The emission color of the microparticles changes from cyan to green when increasing the temperature from 298 to 498 K. Graphical abstract Synthesis of novel Mn(II)-doped Cs3Cu2I5 thermochromic halides with admirable luminescent behaviors for high sensitive ratiometric thermometry and safety sign in high temperature environment.