Laser Cooling of Semiconductor Nanomaterials

Over the past three decades, tremendous amount of effort has been made to realize condensed phase optical cooling. Laser cooling of rare-earth doped glass/crystal first demonstration in 1995 was a great accomplishment. By now, as low as 91 K has been reached from room temperatures. Further cooling, however, becomes problematic due to the electron depopulation at low temperature. To break into the low temperature regime, high purity semiconductors have been suggested. Recently, advances in the synthesis of semiconductor nanostructures have led to the availability of high quality semiconductor nanomaterials, which possess superior optical properties relative to their bulk counterparts as well as rare-earth doped glass/crystal.

The results in this thesis suggest that semiconductor nanostructures are promising cooling media for solid phase optical cooling. Two critical parameters for optical cooling (emission quantum yield and upconversion efficiency) are discussed in detail. In particular, we find CsPbBr3 nanocrystals are ideal candidates for optical cooling because of their near unity emission quantum yield and sizable upconversion efficiency. A numerical simulation of CsPbBr3 nanocrystal optical cooling was subsequently performed. The results of the simulation suggest a minimum cooling temperature of 263K. However, more work needs to be done to demonstrate verifiable solid phase optical cooling.