Resonance Hyper-Raman Scattering from CdSe and CdS Nanocrystals

Resonance hyper-Raman spectra are reported for zincblende and wurtzite CdSe quantum dots (QDs), CdS quantum dots, and CdSe/CdS tetrapods in toluene solution using 808-824 nm excitation. All structures show both Stokes and anti-Stokes fundamental scattering and overtone scattering in the CdS or CdSe longitudinal optical phonon, but the hyper-Rayleigh scattering is much stronger relative to the hyper-Raman in the tetrapods than in the QDs. This may reflect a larger relative contribution of nonresonant and preresonant hyper-Rayleigh scattering in the tetrapods, as suggested by model calculations, or it may be related to the more nearly centrosymmetric structure of the QDs, rendering the hyper-Rayleigh scattering less strongly allowed. The hyper-Raman spectra are similar for wurtzite and zincblende CdSe QDs and for zincblende CdSe QDs with different surface ligands.