Up-conversion emission thermometry for semiconductor laser cooling

The ability to precisely measure temperature is critical to eventually developing semiconductor-based optical refrigerators. Presently, a number of approaches exist for conducting contactless temperature measurements. They are mainly based on the temperature-dependent optical response of materials. A common approach called pump-probe luminescence thermometry (PPLT) uses temperature-dependent shifts of a material's band edge emission energy to assess temperature. PPLT, however, cannot be reliably applied to materials such as CsPbBr3 nanocrystals, which exhibit temperature insensitive band gaps. To overcome this restriction, we have developed a new optical thermometry based on temperature-dependent changes to below gap-excited (anti-Stokes, ASPL) and above gap-excited (Stokes, PL) photoluminescence intensity ratios (i.e. I-ASPL/I-PL). In I-ASPL/I-PL can be used to assess local temperature due to the exponentially sensitive nature of emission up-conversion efficiencies. The developed thermometry is not unique to CsPbBr3 and can be applied other systems found suitable for demonstrating semiconductor-based laser cooling.