Temperature and solvent dependence of CdSe/CdTe heterostructure nanorod spectra

Charge separation is known to occur in heterostructure nanocrystals with type II alignment. Transfer rates have been inferred from ultrafast measurements, but other elements relevant to this process, such as the role of the solvent and the internal degrees of freedom, are still poorly understood. The present study investigates temperature and solvent effects on the optical properties of the charge-separated state in CdSe/CdTe collinear nanorods. The importance of the surrounding medium in the steady state photoluminescence is suggested both in the solvent and temperature studies. The latter also provides evidence that a charge-separated bound state is formed at the interface of the two materials, while states where electron and hole behave as free carriers are only accessible through an activated process in which the interfacial exciton is dissociated. Finally, using a dipole-dielectric continuum model, we found that the optical properties of the charge-separated state in these nanocrystals change as a function of solvent polarity.