Optically Cooling CsPbBr3 Nanoparticles

One photon up-conversion photoluminescence is an optical phenomenon whereby the thermal energy of a fluorescent material is used to increase the energy of an emitted photon compared with the energy of the photon that was absorbed. When this occurs with near unity efficiency, the emitting material undergoes a net decrease in temperature--so called optical cooling. Because the up-conversion is thermally activated, the yield of up-converted photoluminescence is also a reporter of the temperature of the emitter. Taking advantage of this optical signature, here we show that cesium lead trihalide nanocrystals are cooled by as much as 66 K during the up-conversion of 532 nm CW laser excitation. This is the first demonstration of optical cooling of colloidal semiconductor nanocrystals, as well as a new record for optical cooling of any semiconductor system, highlighting the intrinsic advantages of colloidal nanocrystals for this goal.