Ratiometric temperature imaging using environment-insensitive luminescence of Mn-doped core-shell nanocrystals.

We report a ratiometric temperature imaging method based on Mn luminescence from Mn-doped CdS-ZnS nanocrystals (NCs) with controlled doping location, which is designed to exhibit strong temperature dependence of the spectral lineshape while being insensitive to the surrounding chemical environment. Ratiometric thermometry on the Mn luminescence spectrum was performed by using Mn-doped CdS-ZnS core-shell NCs that have a large local lattice strain on the Mn site, which results in the enhanced temperature dependence of the bandwidth and peak position. The Mn luminescence spectral lineshape is highly robust with respect to the change in the polarity, phase and pH of the surrounding medium and aggregation of the NCs, showing great potential in temperature imaging under chemically heterogeneous environment. The temperature sensitivity (ΔIR/IR = 0.5%/K at 293 K, IR = intensity ratio at two different wavelengths) is highly linear in a wide range of temperatures from cryogenic to above-ambient temperatures. We demonstrate the surface temperature imaging of a cryo-cooling device showing a temperature variation of >200 K by imaging the luminescence of the NC film formed by simple spin coating, taking advantage of the environment-insensitive luminescence.