Broadband optical non-linearity induced by charge-transfer excitons in type-II CdSe/ZnTe nanocrystals.

Benefiting from excitonic charge-transfer states, an efficient non-linear optical response is observed in type-II nanocrystals by four-wave mixing when the incident photon energy lies below the bandgaps of constituent semiconductors. The non-linear optical properties in nanocrystals can be manipulated by the band alignment of the core-shell components, which serves as a promising platform to design broadband non-linear optical devices.