First published as an Advance Article on the web 9th 2000 No¿emberThe luminescence properties of nanocrystalline ZnSe : Mn2`prepared via an inorganic chemical synthesis are described. Photoluminescence spectra show distinct ZnSe and Mn2`related emissions, both of which are excited via the ZnSe host lattice. The Mn2`emission wavelength and the associated luminescence decay time depend on the concentration of Mn2`incorporated in the ZnSe lattice. Temperature-dependent photoluminescence spectra and photoluminescence lifetime measurements are also presented and the results are compared with those of Mn2`in bulk ZnSe.

A chemical synthesis is described in which ZnSe:Cu particles slowly grow to a final size of ∼3.5 nm radius in 4 h reaction time. During particle growth, samples are extracted to study the luminescence as a function of particle size and temperature. Quantum size effects are observed to influence both the ZnSe and the Cu2+ luminescence. Temperature-dependent measurements on the luminescence intensity, lifetime, and peak positions are reported and discussed.

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Colloidal CdSe quantum dots were chemisorbed on a gold electrode using a variety of self-assembled monolayers (SAMs) consisting of dithiols and rigid disulfides. After absorption of a photon with an energy larger than the band gap, a long-lived excited state is formed in the quantum dot; this state can decay by electron tunneling via the gold. The rate of photoinduced tunneling was measured directly by intensity-modulated photocurrent spectroscopy (IMPS), and its distance dependence was studied using rigid SAMs separating the Q-CdSe and Au. The tunneling rate was found to depend exponentially on the distance, with a decay length of 2 Å.

A study of the electrochemistry of n-type GaN in an alkaline peroxydisulfate (normalS2normalO82−) solution was used to explain the mechanism of photoetching of the semiconductor under open-circuit conditions. The observed enhancement of the photoetch rate as a result of platinum either directly on or in electrical contact with the semiconductor is shown to be mainly a photogalvanic effect. The factors determining the etching kinetics and surface morphology are elucidated.

The charge carrier dynamics in illuminated nanoporous ZnO electrodes consisting of 5 nm particles were investigated. Stable photocurrent quantum efficiencies of 15−30% and photovoltages of up to 0.4 V were found in the presence of the I-/I3 - redox couple in propylene carbonate. The electronic transport in these ZnO electrodes was fast, the tunneling of electrons from the ZnO particles to the conducting substrate was much slower. The photovoltage as a function of light intensity showed a clear discontinuity. This was related to the indirect recombination kinetics; under open circuit conditions it could take 10 s or longer before a photogenerated electron was transferred to I3 - in solution.