Spectroelectrochemistry of CdSe/Cd_xZn_1–xS Nanoplatelets

Abstract

We report an unexpected enhancement of photoluminescence (PL) in CdSe-based core/shell nanoplatelets (NPLs) upon electrochemical hole injection. Moderate hole doping densities induce an enhancement of more than 50% in PL intensity. This is accompanied by a narrowing and blue-shift of the PL spectrum. Simultaneous, time-resolved PL experiments reveal a slower luminescence decay. Such hole-induced PL brightening in NPLs is in stark contrast to the usual observation of PL quenching of CdSe-based quantum dots following hole injection. We propose that hole injection removes surface traps responsible for the formation of negative trions, thereby blocking nonradiative Auger processes. Continuous photoexcitation causes the enhanced PL intensity to decrease back to its initial level, indicating that photocharging is a key step leading to loss of PL luminescence during normal aging. Modulating the potential can be used to reversibly enhance or quench the PL, which enables electro-optical switching.

Spectroelectrochemistry of CdSe/CdS Core–Shell Quantum Dots

“…16 In addition, a home-built setup was used to conduct time-resolved PL spectroelectrochemistry within the SEC cell. 31 A pulsed laser (λ ex = 470 nm) with a repetition rate of 5 MHz was used to excite charged QDs inside the working electrode volume. Neutraldensity filters were used to control the intensity of the excitation light.…”

“…Steady-state, solution-phase spectroelectrochemistry was conducted with the setup reported previously . In addition, a home-built setup was used to conduct time-resolved PL spectroelectrochemistry within the SEC cell . A pulsed laser (λ ex = 470 nm) with a repetition rate of 5 MHz was used to excite charged QDs inside the working electrode volume.…”

Direct Assessment of Auger Recombination Rates of Charged Excitons via Opto-Electrical Measurements

“…Despite the apparent successes, the above-mentioned methods still face the following limitations: The stir- versus -static measurement permits us to probe only one type of charged exciton of QDs due to incontrollable surface trap states. − The electrochemistry is allowed only for the case where the lowest quantized energy states for the hole (1S h ) and electron (1S e ) of QDs are positioned near the potential of the working electrode; otherwise, unwanted side reactions could occur when high voltage is applied to inject charge carriers into QDs. , The photochemistry is applicable to limited QD samples, whose surfaces are robust against side reactions ( e.g. , oxidation or detachment of ligands) when exposed to oxidizing/reducing agents. , …”

“…24−26 The electrochemistry is allowed only for the case where the lowest quantized energy states for the hole (1S h ) and electron (1S e ) of QDs are positioned near the potential of the working electrode; 30 otherwise, unwanted side reactions could occur when high voltage is applied to inject charge carriers into QDs. 31,45 The photochemistry is applicable to limited QD samples, whose surfaces are robust against side reactions (e.g., oxidation or detachment of ligands) when exposed to oxidizing/reducing agents. 35,39 Herein, we demonstrate a non-destructive opto-electrical method that permits direct evaluation of AR characteristics of positively and negatively charged excitons of QDs.…”

Improved performance of UV-blue dual-band Bi2O3/TiO2 photodetectors and application of visible light communication with UV light encryption

“…In order to achieve multi-target information recognition, PDs with different photoresponses are usually integrated, however integrated detection systems can hardly meet the demand for miniaturisation and convenience of devices, and therefore there is an urgent need to develop single PDs with multi-band photoresponse characteristics. 10,11 A single PD with multi-band light detection capabilities should include ultra-extra wavelengths from UV to terahertz (THZ), 12 dual wavelengths in IR or visible (both detection bands are in the IR or visible range), dual UV-visible or visible-IR wavelengths. 13 Compared with other narrow-band PDs, dual/multi-band PDs have a wider absorption spectrum, which is conducive to the development of multi-functionality of PDs.…”