Fluorescence dynamics and stochastic model for electronic interaction of graphene oxide with CdTe QD in graphene oxide-CdTe QD composite

Abstract

The development of graphene oxide (GO)/semiconductor quantum dots (QDs) hybrid composite remains a frontier area of research to design optoelectronic, photovoltaic, and light harvesting devices based on an electron transfer process. Therefore, the examination of the electron transfer process from QDs to GO as a function of the number of sites of QD and the mean fractional surface coverage of QD by GO sheet with changing the size of QD and concentration of GO is an important issue to manipulate the performance of devices. Here, we have assembled graphene oxide-CdTe QD composite by the attachment of positively charged cysteamine capped CdTe QDs with negatively charged GO. The structural changes due to electronic interaction of graphene oxide with QDs have been evaluated using Raman spectroscopy. The shifting of G-band and increase of I_D/I_G intensity ratio reveal the electron transfer from excited QDs to GO. The fluorescence dynamics of QD has been investigated by time-resolved fluorescence spectroscopy, and the electron transfer rate (2.24 × 10⁸ to 1.18 × 10⁸ s^-1) is found to be decreased with increasing the size of QDs. We analyze the decays of fluorescence by assuming a binomial distribution of number of available sites of QD and the mean fractional surface coverage of QD by GO sheet which control the quenching process. Analysis suggests that the average number of available sites (152 to 396) increases, the mean fractional surface coverage and the total quenching rate (1.3 × 10⁸ to 0.18 × 10⁸ s^-1) are decreased with increasing the size of QD. It is noteworthy that an ∼6 fold increase in the photocurrent is found in this composite device under light illumination. Such graphene oxide-QD functional materials open up new possibilities in solar energy conversion, photovoltaic, and various potential applications.