Construction Of CdTe Quantum Dot Composites And Study Of Their Ultrafast Carrier Dynamics

Semiconductor quantum dots have excellent optical and electrical properties,which make them show great application prospects in solar cells,triplet state sensitization,photocatalysis and so on.However,the strong quantum confinement effect makes the wave functions of photogenerated electrons and holes in semiconductor quantum dots overlap greatly in spatial distribution,which makes the electron-hole recombination rate higher and limits its application in photoelectric conversion and photocatalysis.Secondly,although a variety of mechanisms for quantum dot-sensitized triplet energy transfer have been proposed,there are still controversies and opinions have not yet reached a consensus.In view of the above problems,this paper uses ultrafast spectroscopy to study the effective charge separation in CdTe quantum dots-gold nanoclusters（Au NCs）composite system and the triplet energy transfer process in CdTe quantum dots-anthracenecarboxylic acid（ACA）hybrid system in detail.The main contents of this paper are as follows:（1）Colloidal semiconductor CdTe quantum dots were synthesized in the oil phase by high-temperature thermal injection method.Further,CdTe quantum dots with good water solubility were obtained by transferring CdTe quantum dots from the oil phase to the aqueous phase using mercaptopropionic acid by the ligand exchange method.Au clusters protected by L-arginine against 6-aza-2-thiothiazine were synthesized by the solvent method at room temperature（Arg/ATT-Au NCs）.The synthesized CdTe quantum dots and Au NCs were characterized by steady-state absorption spectroscopy,steady-state fluorescence spectroscopy,and transmission electron microscopy.The excitonic absorption and emission peaks of CdTe quantum dots were located at～620 nm and～640 nm,respectively,with a size of～5 nm.The Au NCs showed discrete energy-level absorption at 398 nm,467 nm,and 496 nm with a size of～1.7 nm.（2）Nanocomposites of CdTe QDs and Au NCs were constructed,and the ultrafast carrier dynamics and optoelectronic properties in the composites were investigated.The formation of a Type II energy band structural arrangement between CdTe QDs and Au NCs in the composites was demonstrated by steady-state fluorescence spectroscopy and time-resolved fluorescence spectroscopy,which effectively promoted the photogenerated charge transfer between CdTe QDs and Au NCs,thus improving the photocurrent response of the composites.The measurement of femtosecond transient absorption spectra directly observed the ultrafast thermal electron transfer process from CdTe QDs to Au NCs under optical excitation.Analysis of the data reveals that the thermal electron transfer rate from CdTe QDs to Au NCs under 530 nm excitation is1.01×10¹³ s^-1,with a transfer efficiency of 50%.This work has important implications for the development of light trapping and optoelectronic devices based on semiconductor quantum dots and Au clusters.（3）A hybrid system of CdTe QDs-ACA was constructed using CdTe quantum dots as the sensitizer and ACA molecules as the triplet state energy acceptor,and the triplet state energy transfer（TET）pathway and single-linear state oxygen generation properties were investigated in this system.The results of steady-state and time-resolved spectroscopy show that the TET efficiency of CdTe quantum dots to ACA molecules under optical excitation exceeds 80%.Kinetic analysis clearly reveals the presence of two TET channels mediated by hot and thermalised electron exchange in the CdTe QDs-ACA system.Under 530 nm excitation,the TET efficiencies mediated by the two channels are 27%and 85%,respectively.The efficient TET efficiencies gives the CdTe QDs-ACA hybrid system a good single-linear state oxygen production capability,with yields of～59%.These findings contribute to an in-depth understanding of the mechanism of TET action at the interface between semiconductor quantum dots and organic molecules,and are important for the design of efficient triplet state energy transfer systems based on semiconductor quantum dot sensitization.