Time-Resolved Spectroscopic Study of Charge Transfer Dynamics of Quantum Dots and Au-rod-TiO2 Nanocomposite

Abstract

Time resolved spectroscopic technique has been applied for study of photo physical properties and photo dynamics of transient species. This technique has its own distinct advantage which enables us to study transient species including excited states, intermediates and transition state. The focus of this work has been probed in charge transfer dynamics and carrier relaxation of QDs and semiconductor by time resolved spectroscopic techniques which are fully employed to study and understand excited state dynamics and their novel chemical properties.

Quantum dots are tiny particles, or nanoparticles, of a semiconductor material, traditionally chalcogenides (selenides or sulfides) of metals like cadmium or zinc (CdSe or ZnS, for example), which range from 2 to 10 nanometers in diameter. Because of their small size, quantum dots display unique optical and electrical properties that are different in character to those of the corresponding bulk material. Moreover, the wavelength of emissions depends not on the composition of the quantum dot, but its size. Quantum dots can therefore be tuned during production to emit any color of light desired by changing its size. We synthesized a new highly QDs using multi shell structures and investigated its stability and photo properties. Passivation of QDs such as InP is reported to increase the quantum efficiency and stabilize its structure by protecting the core from external environments. We verified the charge transfer dynamics of InP QDs passivated with GaP and ZnS shell by using time-correlated single photon counting spectroscopy.

Semiconductor and metal nanoparticles display unique size dependent photo physical, electrochemical, photo catalytic and optical properties. The presence of metal facilitates electron transfer from photo excited semiconductor to the surroundings and decreases recombination rate between the electrons-holes in the semiconductor. The focus of this work provides mechanistic explanation for the size-dependent charge recombination rate of TiO2 and Au rod/TiO2 composite in UV region. We have found that the TiO2 shell thickness and Au rod have influenced the charge recombination of TiO2 by transient absorption spectroscopy.