Synthesis and fabrication of scattering Ag nanoparticle films
We are exploring the synthesis and development of monolayer Ag nanoparticle films for use in metal enhanced absorption and fluorescence applications. Depending on their morphology, Ag nanoparticles can scatter some parts of the optical spectrum significantly more than they absorb. In these studies we are exploring synthetic methods to control their scattering properties and chemically attach them to glass substrates.
Biosensing with DNA/Quantum dot conjugates
We have demonstrated a new method for quantum dot-based biosensing using DNA. Selective binding to an analyte induces particle aggregation, which is detected using single particle spectroscopy. This method does not rely on complex FRET or electron transfer interactions between the sensor and the quantum dot and can be applied generally to a wide range of target molecules
Colloidal core/shell Au/CdS and Au/ZnS nanoparticles
Au/CdS and Au/ZnS particles are proposed as a controllable way to exploit exciton-plasmon coupling to enhance absorption and emission rates of surface-attached chromophores including QDs (CdSe, PbS, etc) and molecules (porphyrins). In this project we explore ways to synthesize these nanoparticles (NPs) and develop strategies to selectively bind QDs and molecules to their surface.
Multi-pulse time-resolved fluorescence methods
Fluorescence decays from multiexcited states in colloidal QDs are difficult to separate from exciton fluorescence because they are usually weak and spectrally overlapping. In this project we are developing new ensemble multi-pulse time-resolved spectroscopic methods that allow us to distinguish multiexcited state fluorescence dynamics from exciton decays and assign the emitting states.
Single particle studies of QD fluorescence near Au NPs
Exciton-plasmon coupling between QDs and gold NPs can enhance QD absorption end emission rates. However, its dependence on interparticle distance and morphology is poorly understood. In this project we aim to fabricate layered structures that enable us to control the separation between Au NPs and QDs and measure their emission using confocal fluorescence microscopy.
Fluorescence dynamics in near-IR emitting QDs
Near IR emitting PbS and PbSe QDs have an ideal band gap for harvesting sunlight. Utilizing multiple exciton generation (MEG) PbSe solar cells have already achieved > 100% efficiencies for blue photons. Coupling IR QDs to gold NPs may enhance MEG efficiencies by increasing absorption rates above the MEG threshold. In this project we aim to synthesize PbS and PbSe QDs and study their time-dependent emission near gold NPs.
Carrier trapping and its affect on QD recombination dynamics
Fluorescence dynamics in II/VI and IV/VI QDs are affected by surface sites that can trap electrons or holes. These limit emission quantum yields and can slow carrier transport in QD films. In this project we use advanced kinetic analysis methods to model temperature-dependent time-resolved fluorescence and unravel the factors that control electron and hole trapping and detrapping rates in colloidal QDs.
Hole transfer dynamics in CdSe/thioether systems
Thioethers developed in collaboration with the Rabinovich group have been shown to act as hole acceptors when ligated to CdSe quantum dots (QDs). In this project we will use time-resolved fluorescence and isothermal titration calorimetry to determine the factors that control hole transfer rates between CdSe and several bis-thioether molecules with a range of HOMO energies.