Optical characterization of type-II CdTe/CdSe/CdTe heterostructure nanorods

The optical characteristics of an indirect type II transition in a series of size and shape-controlled linear CdTe/CdSe/CdTe heterostructure nanorods was studied by steady state and time resolved photoluminescence spectra. The energy and lifetime of the photoluminescence from the charge-separated band structure can be tuned by the band edges of the nanorods. Our results show a size-dependent transition from a type I direct transition (CdSe~600 nm) to an indirect type II transition (CdSe/CdTe). The heterostructure nanorod geometry and dimensions that induce type-II charge separation without type-I recombination were determined. The indirect type II transition at 5 K exhibited a long PL decay time, of more than 1000 nanoseconds, that increased with PL wavelength, which can be rationalized by the changing of wavefunction overlap of electrons and holes induced by the quantum confinement effect in type-II band structure.