Systematic investigation of the structure and photophysical properties of CdSe, CdSe/ZnS QDs and their hybrid with β-carotene

Abstract

A systematic investigation was conducted to determine the excitation energy dependent emission characteristics of CdSe quantum dot-b-carotene and CdSe/ZnS core-shell quantum dot-b-carotene hybrid samples. The emission intensity was recorded at different excitation energies by continuously varying the excitation energy from the band edge value of the QDs to a maximum value. In both the hybrids, the emission intensity increased with an increase of the excitation energy and then a sudden quenching occurred, which is in contrast with the results from bare samples, where the emission intensity showed a decreasing trend at all excitation energies. The quantum yields corresponding to the maximum emission are 47.12% and 69%, for CdSe QD-bC and CdSe/ZnS core-shell QD-bC hybrids, respectively. At higher excitation energy, electrons were transferred to the molecule's LUMO level, leaving behind holes in the valance band of the QD, and thus the produced charge separated state became responsible for the PL quenching in the hybrid sample. We have confirmed this charge separated state by lifetime measurements. It is because of this PL quenching behaviour of the hybrids that the nature of the interface band structure was deduced as type I. Furthermore, because of the involvement of higher energy photons in the quenching process, the transferred electrons in the LUMO level of the molecule were known as hot electrons. The present paper discusses the excited state electron dynamics across the interface between the two hybrid materials in detail.

Highly Photoluminescent InP Based Core Alloy Shell QDs from Air-Stable Precursors: Excitation Wavelength Dependent Photoluminescence Quantum Yield, Photoluminescence Decay Dynamics, and Single Particle Blinking Dynamics

“…Our results indicate that, with increasing excitation/exciton energy, the surface mediated nonradiative pathways predominate over relaxation of the charge carrier to the emitting lowest energy states. Similar observation has been observed for CdSe based QDs. − The high energy charge carrier perhaps undergoes nonradiative barrierless tunneling to the trap states of the surface passivating ligands of the QDs, ,, and thus, contribute to the decrease of the PLQYs observed for excitations at shorter wavelength range. A sudden decrease in PLQY is observed at about 375 nm (or below) excitation.…”

“…Interestingly, PLQY has been observed to increase monotonically with increasing excitation wavelength for all four different QDs (Figure ). Excitation wavelength dependent PLQY has been reported recently for the CdSe based QD; − however, this is the first report of excitation dependent PLQY for InP based CAS QD. Please recall that the same observation was expected from the observed deviation of the PL excitation spectrum from the absorption spectrum .…”

Paper-Based Simplified Visual Detection of Cry2Ab Insecticide from Transgenic Cottonseed Samples Using Integrated Quantum Dots–IgY Antibodies

“…The increase in R H and ζ was due to the agglomeration of QDs by the conjugation of antibodies on the surface and the detachment of carboxyl ligands from the surface of the QDs . The comparison of emission spectra (Figure c) of both QDs and antibody-conjugated QDs has proven that the conjugation of antibodies on the surface of quantum dots caused photoluminescence (PL) quenching by nonradiative electron hole recombination of the QDs . This electron trapping by the antibodies could be reversed when an analyte was added to the solution, leading to PL enhancement.…”

“…28 The comparison of emission spectra (Figure 1c) of both QDs and antibodyconjugated QDs has proven that the conjugation of antibodies on the surface of quantum dots caused photoluminescence (PL) quenching by nonradiative electron hole recombination of the QDs. 29 This electron trapping by the antibodies could be reversed when an analyte was added to the solution, leading to PL enhancement. MPA-capped CdTe QDs exhibit a strong emission peak with unchanged full width at half-maximum after conjugation of antibodies that supports the strong conjugation of QDs with IgY antibodies.…”

Luminous block copolymer–quantum dots hybrids formed by cooperative assembly in a selective solvent

“…In addition to their better photostability, semiconductor nanocrystals are superior to organic dyes in other aspects, such as broader excitation and narrower emission spectra, which can be easily tuned. [38][39][40] Cooperative selfassembly of amphiphilic BCPs and semiconductor NPs offers a powerful route to fabricate functional hybrid materials.…”