We show that by placing a single CdSe/ZnS quantum dot ͑QD͒ near a high-reflective optical mirror, both the photoluminescence intensity and the blinking statistics can be modified significantly and controlled deterministically by changing the dot-mirror distance. The modified local optical mode density in proximity to the QD alters the internal dynamics of the QD, which controls its blinking behavior. Such external controls of single-QD blinking can help us to better understand the underlying mechanism of the blinking process and lead to interesting applications of such QDs.Fluorescence intermittency ͑blinking͒ is a universal property of single colloidal semiconductor quantum dots ͑QDs͒, 1 which can greatly affect the applications of QDs in biological labeling, 2 optoelectronic devices, 3 and single-photon sources. 4 Therefore, it is very important to find ways either to suppress or to control the blinking phenomenon in the QDs. 5-8 Efforts have been made to suppress the intermittency phenomenon by using chemical procedures, where the durations of the "on" time are increased considerably by surface passivation 5 or by increasing the shell thickness around the core 6 to modify the charge tunneling process. 7 An external modification of intermittency process was observed when the single CdSe/ZnS QD was placed in the proximity to a rough metal surface. 8 When a light emitter is placed inside a small optical cavity, its emission properties, such as radiative lifetimes, emission spectra, and quantum statistical properties of the field, will be greatly modified, leading to an active field of research called cavity-quantum electrodynamics ͑cavity-QED͒. 9-12 If only one cavity mirror is present near the light emitter, the system is viewed as a half cavity with the light emitter coupling to a large number of field modes or can be considered as in the "low-Q" regime of cavity-QED. 10 Depending on the distance between the light emitter and the mirror, there are two regions for studying the emitter-mirror interactions. When the light emitter is far from the mirror with a distance in the order of tens of centimeters, the reflected light from the mirror is significantly delayed and the interaction processes become non-Markovian. 10 Interesting effects under this condition were studied by using a trapped Ba + ion placed long distance from a high-reflective mirror. 11,12 However, when a light emitter is placed very near the dielectric mirror ͑in the order of wavelength of the emitted light͒, the interaction processes are Markovian. 10 Modified average radiative lifetime was measured for an ensemble of CdSe/CdS QDs near a reflective surface with an oscillatory behavior as the average dot-mirror distance changed. 13 In this Rapid Communication, we experimentally demonstrate that when a single CdSe/ZnS QD is placed near a highly reflective dielectric mirror ͑in the Markovian regime͒, not only the photoluminescence ͑PL͒ intensity is modified when the dot-mirror distance is changed but the PL intermittency behavior also gets significa...
The effects of spacer thickness on lateral alignment and density of InGaAs quantum dots on GaAs(311)B substrates is investigated. As the thickness of the spacer layers is increased, the two-dimensional lateral ordering previously demonstrated on GaAs(311)B is replaced by the one-dimensional dot chains normally observed on GaAs(100). Additionally, the dot density is found to increase proportionally with spacer thickness. The transition of lateral alignment regimes results from two processes competing to dominate the growth mechanism: the elastic anisotropy of the matrix and the characteristics of surface diffusion.
Photoconductivity spectra of monocrystals of CdIn2S4, some of which were annealed in a sulphur-rich atmosphere, have been studied in order to understand the origin of the high photosensitivity. It is found that sulphur enriched CdIn2S4 shows a high photoresponse. The data presented explain observed discrepancies in the band gap values. An origin for the slow photoresponse is also examined.
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