Surface‐State‐Mediated Charge‐Transfer Dynamics in CdTe/CdSe Core–Shell Quantum Dots

Abstract

Herein, we report the synthesis of aqueous CdTe/CdSe type-II core-shell quantum dots (QDs) in which 3-mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core-shell QDs are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), steady-state absorption, and emission spectroscopy. A red shift in the steady-state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR-TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time-resolved emission studies, we observe that the average emission lifetime (τ(av)) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (τ(av) =12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type-II CdTe/CdSe core-shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge-transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core-shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core-shell QDs.

Ultrafast exciton dynamics in Type II ZnTe–ZnSe colloidal quantum dots

“…6 Secondly, they are the only Type II CQD yet demonstrated to emit at wavelengths less than 500 nm, thus enabling gain in the blue part of the spectrum. [11][12][13][14][15][16][17][18][19][20][21] Lastly, they are also unique amongst Type II CQDs in being free of toxic elements such as Cd and Pb, the use of which is heavily restricted by legislation. 22 This study has shown, as for CdSe and PbSe CQDs, that the surface-trapping of photogenerated charges can play an important role in the sub-nanosecond exciton dynamics of ZnTe-ZnSe CQDs.…”

“…[8][9][10] To date ultrafast exciton dynamics have been studied in Type II CQDs utilising CdE (E = Se, S or Te) for either the core or shell material, or both. These core-shell structures have included CdS-ZnSe, 6 ZnTe-CdSe, 11 CdTe-CdSe, [12][13][14][15][16] ZnSe-CdS, 17 CdTe-CdS, 18 CdSe-ZnTe, 19 CdTe-ZnTe 20 and CdSe-ZnS. 21 However, the use of cadmium is heavily regulated because of its toxicity by, for instance, the Restriction of Hazardous Substances Directive of the European Union; 22 other jurisdictions have similar legislation.…”

“…>500 nm). [11][12][13][14][15][16][17][18][19][20][21]24 The synthesis of a Type II CQD based entirely on ZnE (E = Se, S and Te) has only recently been reported. 23,25 In the first of those works, the authors fabricated and characterised both ZnTe-ZnSe core-shell and ZnTe-ZnSe-ZnS core-shell-shell heterostructures, and also investigated the performance of hybrid CQD/polymer photovoltaic cells incorporating them.…”

Ultrafast Charge Separation for Full Solar Spectrum-Activated Photocatalytic H2 Generation in a Black Phosphorus–Au–CdS Heterostructure

“…This could probably be explained by the more intense electron−hole feature from the dangling bond of BP as a result of the aggregation of BP on the CdS surface. 37 Comparison between the normalized transient absorption dynamics for the bleach recovery at 737 nm is presented in Figure 4b for the different BP-mediated materials. In bare BP QDs, as summarized in Table 1, two fast decay components were observed, which could be ascribed to the exciton recovery to the ground state (1.7 ps) and residual cooling of the trapped electrons in superficial defect states of BP (10 ps), respectively.…”

Preparation and Fluorescence Properties of Aqueous Soluble Thiourea Modified ZnSe:Cu Quantum Dots

“…点,[18][19][20] 近年来也有关于 ZnSe/ZnS 量子点的报道,[21][22][23] 但目前对 Cu 掺杂的 ZnSe 量子点表面修饰的研究报 道 较 少, 主 要 是 以 TAA 和 Na2S 24,25 为 硫 源 制 得 的 ZnSe:Cu/ZnS 量子点为主,…”