Femtosecond Time-resolved Studies of Quantum Dots-Based Energy Transfer
Energy transfer (ET) is one of the fundamental processes for photoexcited systems. Fluorescent semiconductor quantum dots (QDs) are promising inorganic fluorophores for ET applications due to their unique optical and spectroscopic properties. Some of the outstanding properties of QDs for ET related studies include broad tunable absorption spectra with high molar-extinction coefficients, narrow and symmetric emission spectra providing better spectral resolution, ability to modify the surface of the QDs, tunable emission spectra from UV to near IR spectral range with high fluorescence quantum yields. In addition, QDs also provide high-resistance to photobleaching and large Stokes’ shift between absorption and emission spectra leading to better spectral resolution.
On the other hand, QDs are an order of magnitude larger than molecules and consist of ~100-10000 atoms per QD. They also have very high surface to volume ratio and surface energy that may have some significant effect and channels for ET in QD-based systems. Recent reports show that QD exhibit deviation from ET theories developed for both molecules and bulk materials.
In this dissertation, we focus on the fundamental issues related to these QD-based ET pairs and investigate the influence of various parameters such as: donor-acceptor distance, spectral overlap integral, electronic coupling and the donor quantum yield on ET efficiency and dynamics. The conjugates of QD with silicon-phthalocyanine derivatives are synthesized as ET donor-acceptor pair and the mechanism of the ET process in these systems is investigated by steady state and femtosecond time-resolved absorption spectroscopy with a resolution of 120 fs. Compared to molecular system, studied QD-conjugate DA pairs are found to be unique and show deviations from the ET theories derived for molecular system.
QDs also provide the opportunity of the near Infrared excitation for the biomedical applications such as imaging and labeling. We demonstrate the two-photon excitation of the QDs followed by sensitization of acceptor molecule with near IR wavelengths. In addition, the composition tunability of ternary QDs CdSexTe1-x¬ fluorescence leading to near IR emission is explored. These ternary nanoparticles show far red and near infrared fluorescence properties compared to binary CdSe and CdTe nanoparticles and are potential candidates for biological imaging and labeling applications.
School:Case Western Reserve University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:quantum dots energy transfer two photon excitation
Date of Publication:01/01/2008