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Easily disrupted: Micelles of a new amphiphilic block copolymer that bear coumarin groups are sensitive to near infrared light by two-photon absorption of the chromophore. Disruption of the micelles under irradiation at 794 nm results in release of both photocleaved coumarin and encapsulated nile red from the hydrophobic core of micelle into aqueous solution, which results in opposing changes in fluorescence emission intensity.

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Carrier relaxation processes are investigated in self-assembled InAs/GaAs quantum dots using time-resolved photoluminescence spectroscopy. The quantum-dot photoluminescence rise time has been measured as functions of carrier excitation density and excitation wavelengths. The measured relaxation time is about 32 ps at low excitation density and decreases by 1 over the excitation density from about 3 W/cm2, under nonresonant laser excitation. The threshold of this density-dependent regime occurs at a slightly higher density as the excitation wavelength increases and it disappears when the photon pumping energy is below the wetting layer barrier energy. These results clearly establish the regime where Auger processes become the dominant carrier relaxation mechanism in these self-assembled quantum dots.

Photocorrosion of semiconductors is strongly sensitive to the presence of surface states, and it could be influenced by electrically charged molecules immobilized near the semiconductor/electrolyte interface. The underlying mechanism is related to band bending of the semiconductor structure near the surface and the associated distribution of excited electrons and holes. The authors have employed photoluminescence of GaAs/AlGaAs quantum heterostructures for monitoring in situ the photocorrosion effect, and demonstrating detection of nongrowing Legionella pneumophila suspended in phosphate buffered saline solution. Antibody functionalized samples allowed direct detection of these bacteria at 10(4) bacteria/ml. The authors discuss the sensitivity of the process related to the ability of creating conditions suitable for photocorrosion proceeding at extremely slow rates and the interaction of an electric charge of bacteria with the surface of a biofunctionalized semiconductor.