Charge Transfer Dynamics and Auger Recombination of CdTe/CdS Core/Shell Quantum Dots

Abstract

Core/shell semiconductor nanocrystals can be designed to afford type I, quasi-type II, or type II energy-band alignments, differing in the nature of the carrier-relaxation processes. In this study, we synthesized CdTe/CdS core/shell quantum dots (QDs) from four differently sized CdTe core QDs by a hydrothermal method, and we examined their exciton-relaxation dynamics by time-resolved luminescence and transient absorption (TA) spectroscopies. We performed core/shell-selective excitation experiments on large CdTe/CdS core/shell QDs with tetrahedral structures. The relative bleach TA intensities at the 1S state against the lowest exciton state of the CdS shell are different for the core and the shell excitations. We interpret this phenomenon in terms of a small potential barrier in the conduction band, induced by grain boundaries at the core/shell interface of CdTe/CdS core/shell QDs. The evolution of the band alignment from type I to quasi-type II is confirmed by increased luminescence lifetimes, hole localization in the core, and electron delocalization throughout the QD. Moreover, the biexciton Auger recombination lifetime (τ Auger ) of CdTe/CdS core/shell QDs represents a luminescence wavelength dependence that is similar to that of CdTe QDs, which is further support for the quasi-type II band alignment. In the present of potential energy barrier, τ Auger of the large CdTe/CdS core/shell QDs becomes elongated. This study offers a useful guideline for determining the energy-band alignment of semiconductor nanoheterostructures not only according to luminescence lifetimes and exciton-relaxation kinetics but also τ Auger .

Shell effects on hole-coupled electron transfer dynamics from CdSe/CdS quantum dots to methyl viologen

“…25 The use of small core QDs, thereby increasing the wavefunction energies, allows for clear distinction of these two states separated by 110 meV, which was not the case in the work of Dworak et al, 17 but was achieved in the work of Liu et al 24 The increasing absorbance in the blue (<550 nm) with increasing CdS shelling is due to the large extinction coefficient of CdS in this spectral region. 12,26 3.2 Femtosecond transient absorption spectroscopy Fig. 2a-c show TA spectra at different delay times up to 700 ps after 400 nm excitation of different core/shell QDs in the absence and presence of MV 2+ .…”

Breaking Out the Traditional Polymerization: Tailoring the Shape, Structure, and Optical Properties of Polydopamine by Using CdTe Quantum Dots

“…On the other hand, the core–shell CdTe@CdS QDs maintain the traditional growing of spherical PDA particles (see Figure S6c, Supporting Information). The covering of CdTe core with CdS leads to recombination of an electron in CdS and a hole in CdTe, which could affect the necessary charge transfer between QDs and polydopamine to obtain the blue particles.…”

Core–shell structured CdTe/CdS@SiO2@CdTe@SiO2 composite fluorescent spheres: Synthesis and application for Cd2+ detection

“…Red‐emissive CdTe/CdS QDs were obtained by depositing CdS on the as‐prepared CdTe QDs core . The CdTe precursor was refluxed for 2 h to produce the CdTe core.…”

“…After heating and stirring for 1 h at 70°C, the colorless ethanol solution of NaHTe produced was mixed with 5 ml of Red-emissive CdTe/CdS QDs were obtained by depositing CdS on the as-prepared CdTe QDs core. [28][29][30] The CdTe precursor was refluxed for 2 h to produce the CdTe core. Then, 20 mg of CdCl 2 ·2.5H 2 O and 20 μl of MPA were added to the cooled CdTe core solution at pH 9.5, followed by heating to 50°C.…”