Two-photon absorption in CdSe colloidal quantum dots compared to organic molecules.

We discuss fundamental differences in electronic structure as reflected in one- and two-photon absorption spectra of semiconductor quantum dots and organic molecules by performing systematic experimental and theoretical studies of the size-dependent spectra of colloidal quantum dots. Quantum-chemical and effective-mass calculations are used to model the one- and two-photon absorption spectra and compare them with the experimental results. Currently, quantum-chemical calculations are limited to only small-sized quantum dots (nanoclusters) but allow one to study various environmental effects on the optical spectra such as solvation and various surface functionalizations.

An effective nanosensor for organic molecules based on water-soluble mercaptopropionic acid-capped CdTe nanocrystals with potential application in high-throughput screening and high-resolution optical microscopy.

Specially-treated glass substrates coated with a thin film of water soluble mercaptopropionic acid (MPA) capped CdTe nanocrystals (NCs) were prepared and found to undergo photoluminescence changes by as much as 40% when micro-droplets of organic molecules were placed in the nanometer-range proximity of the NCs. This imaging technique involving close proximity between a nano-crystal and an organic molecule is found to provide a 2 × -3 × enhanced contrast ratio over the conventional method of fluorescence imaging. Photoluminescence of NCs is recoverable upon removal of the organic molecules, therefore validating these NCs as potential all-optical organic molecular nanosensors.

Thermally robust and blinking suppressed core/graded-shell CdSe/CdSe1-xSx/CdS 'giant' multishell semiconductor nanocrystals.

We demonstrate that core/graded-shell CdSe/CdSe1-xSx/CdS giant semiconductor nanocrystals (g-NCs) have robust photoluminescence (PL) temperature response. At a size of 10.2 nm in diameter, these g-NCs undergo a PL drop of only 30% at 355 K relative to their PL intensity at 85 K.

An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals.

CdTe semiconductor nanocrystals (NCs) with 3-mercaptopropionic acid as the ligand exhibit a reversible response towards inter-switching oxygen and argon environments. The photoluminescence response is investigated at multiple oxygen concentrations, NC coverage and excitation intensities, in which all conditions exhibit full recovery upon exposure to flowing argon. The CdTe NC's large surface-to-volume ratio results in high sensitivity towards oxygen molecules with significant photoluminescence quenching at a concentration of 40 ppm.