Considerable research has been carried out on colloidal semiconductor nanocrystals (NCs) on account of their size dependent electronic and optical properties, which are the key issues in many applications, such as biomedical fluorophores, 1 LEDs, 2 and photovoltaic devices. 3 Among them, a group of II-VI semiconducting NCs, for example, CdSe quantum dots (QDs), exhibit excellent photostability, quan-tum yield (QY), and a tunable emission wavelength. 4,16 However, CdSe QDs have limited applications owing to their intrinsic toxicity. 5 It is believed that III-V QDs, particularly InP NCs, are the most desirable alternative. However, the photoluminescent quantum yield tends to be very low due to nonradiative surface recombination sites and high activation barriers for carrier detrapping. 6,7 A core-shell structure appears to be essential for surface passivation, but limited numbers have been reported, including InP/ZnS 8,9,14,15 and InP/ZnCdSe 10 core/shell QDs. HF etching 11,13 and low reaction temperature methods have also been attempted. In particular, the recent reports by Peng's group on highly luminescent InP/ZnS core-shell quantum dots in the visible range using fatty amine 9 and Reiss on the one-pot synthesis of InP/ZnS 14 are quite impressive.We report the stepwise synthesis of InP/ZnS core-shell quantum dots and the role of zinc acetate during the reaction. Zinc acetate was used as a precursor for zinc and acetic acid. Highly luminescent InP/Zn-palmitate was obtained as an intermediate. The InP core was synthesized with indium acetate (In(OAc) 3 ), tris(trimethylsilyl)phosphine ((TMS) 3 P), and palmitic acid as the indium and phosphorus precursors

An efficient quenching of the photoluminescence spectrum was observed for the quantum dot (QD)-multiwalled carbon nanotubes (MWCNTs) nanocomposite. While the lifetime of the blue emission from ZnSe shell was significantly reduced, it did not exhibit any obvious change in the red emission from CdSe core-crystal. This difference revealed two competing charge transfer processes between the CdSe core-crystal, the ZnSe shell and the MWCNTs. Current-voltage measurements on devices fabricated utilizing CdSe QD-MWCNT nanocomposites showed photovoltaic (PV) effect under ultraviolet light illumination. Charge transfer mechanisms of the PV cells are described on the basis of the experimental results.

Transmission electron microscopy images showed that conjugation between single core-shell CdSe/ZnSe quantum dots (QDs) and oxidized multi-walled carbon nanotubes (MWCNTs) was achieved through the complexation reaction. Current-voltage (I-V) measurements on Al/CdSe:MWCNT conjugated nanocomposite/indium-tin-oxide devices at 300 K showed that the on/off ratio of the current bistability was as large as about 10(4), which was significantly increased due to an enhancement of the carrier transfer efficiency between the CdSe/ZnSe QDs and the MWCNTs. Carrier transport mechanisms of the bistable memory devices fabricated utilizing CdSe/ZnSe QD/MWCNT hybrid nanocomposite are described on the basis of the I-V results.

Nonvolatile memory devices were fabricated with core-shell CdTe-CdSe nanoparticles embedded in a poly(9-vinylcarbazole) (PVK) layer to investigate the variations in the electrical properties due to a CdSe shell layer. Capacitance-voltage measurements on Al/CdTe nanoparticles embedded in PVK layer/p-Si devices and on Al/core-shell CdTe-CdSe nanoparticles embedded in PVK layer/p-Si devices at 300 K showed hysteresis behaviors with a flatband voltage shift due to the existence of the CdTe and the CdTe-CdSe nanoparticles. Capacitance-time measurements showed that the retention time for devices fabricated utilizing core-shell CdTe-CdSe nanoparticles was larger than that for devices fabricated utilizing CdTe nanoparticles.