Effect of Controlled Deposition of ZnS Shell on the Photostability of CdTe Quantum Dots as Studied by Conventional Fluorescence and FCS Techniques

Abstract

The effect of one and two monolayers of ZnS shells on the photostability of CdTe quantum dots (QDs) in aqueous and nonaqueous media has been studied by monitoring the fluorescence behavior of the QDs under ensemble and single-molecule conditions. ZnS capping of the CdTe QDs leads to significant enhancement of the fluorescence brightness of these QDs. Considerable enhancement of the photostability of the shell-protected QDs, including the suppression of photoactivation, is also observed. Fluorescence correlation spectroscopy measurements reveal an increase in the number of particles undergoing reversible fluorescent on-off transitions in the volume under observation with increasing excitation power; this effect is found to be more pronounced in the case of core-only QDs than for core-shell QDs.

Fluorescence Blinking and Photoactivation of All-Inorganic Perovskite Nanocrystals CsPbBr3 and CsPbBr2I

“…FCS is a noninvasive single-molecule-based sensitive technique in which fluctuations of the fluorescence intensity in a small volume (∼1 fL) is monitored to obtain information relating to the process responsible for fluctuation. This technique has recently been applied to understand the fluorescence intensity fluctuation of metal–chalcogenide quantum dots (QDs) in the microsecond time domain. − The present FCS study on CsPbBr 3 and CsPbBr 2 I in a nonpolar and noninteracting medium, 1-octadecene (ODE), is undertaken considering that the fluorescence correlation curves can provide valuable information relating to the charge separation and recombination processes. Conventional steady-state and time-resolved fluorescence measurements have also been performed to supplement the FCS results.…”

“…The FCS data is fitted to a model (eq ), which involves a diffusion component and a stretched exponential decay component. This widely accepted fitting model has been used previously for metal–chalcogenide quantum dots (QDs). − , The fit quality to eq and a few other attempted models are provided as Supporting Information (Figures S3–S5). where N is the average number of NCs in the observation volume undergoing reversible fluorescence off–on transition, T the off-state fraction, τ T the off-state relaxation or blinking time, τ D the time taken by the particle to diffuse through the observation volume, β (0 < β < 1) the stretching exponent representing the distribution of τ T , and κ the structure parameter of the observation volume.…”

“…This widely accepted fitting model has been used previously for metal−chalcogenide quantum dots (QDs). [28][29][30][31]35 The fit quality to eq 3 and a few other attempted models are provided as Supporting Information (Figures S3−S5).…”

Single-Particle Dynamics of ZnS Shelling Induced Replenishment of Carrier Diffusion for Individual Emission Centers in CuInS2 Quantum Dots

“…However, light-induced charging and neutralization can lead to photoactivation with a drop of G(0) even for CIS-ZnS. As has been reported from other core−shell QDs 36,58,59 the mechanism possibly involves a shift of equilibrium between electron ionization and electron recombination plausibly from the structural rearrangements brought by the carriers toward their way to the surface after Auger recombination 58,59 or with adsorption of water molecules that hinder electron ionization by Coulomb blockade. 36,61 The diffusion times (τ D ) increase slightly with power in both CIS and CIS-ZnS (Figure S5), indicating aggregation of QDs in high fluence, as observed in previous studies.…”

Detection of Hg2+ by a Dual-Fluorescence Ratio Probe Constructed with Rare-Earth-Element-Doped Cadmium Telluride Quantum Dots and Fluorescent Carbon Dots

“…Fluorescent probes are widely used for detection and analysis as they are simple, highly sensitive, and precise. − Quantum dots (QDs) are tiny semiconductor materials that are widely used as fluorescent probes as they exhibit excellent optical properties. However, the toxicity of the Cd element limits the application of Cd QDs as fluorescent probes.…”