Photocurrent derivative spectra of ZnCdSe-ZnSe double multi-quantum wells

Photocurrent (PC) spectra of ZnCdSe-ZnSe double multi-quantum wells are measured at different temperature. Its corresponding photocurrent derivative (PCD) spectra are obtained by computing, and the PCD spectra have greatly enhanced the sensitivity of the relative weak PC signals. The polarization dependence of the PC spectra shows that the transitions observed in the PC spectra are heavy-hole related, and the transition energy coincide well with the results obtained by envelope function approximation including strain. The temperature dependence of the photocurrent curves indicates that the thermal activation is the dominant transport mechanism of the carriers in our samples. The concept of saturation temperature region is introduced to explain why the PC spectra have different temperature dependence in the samples with different structure parameters. It is found to be very useful in designing photovoltaic devices.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

Total-internal-reflection fluorescence microscopy with W-shaped axicon mirrors

A scheme based on a W-shaped axicon mirror device for total-internal-reflection fluorescence microscopy (TIRFM) is presented. This approach combines the advantages of higher efficiency compared with traditional TIRFM, adjustable illumination area, and simple switching between wide-field and TIRF imaging modes. TIRF images obtained with this approach are free of shadow artifacts and of interference fringes. Example micrographs of fluorescently labeled polystyrene beads, of Convallaria majalis tissue, and of Propidium-iodide-labeled Chinese hamster ovary cells are shown, and the capabilities of the scheme are discussed. (C) 2010 Optical Society of America

Multifunctional darkfield microscopy using an axicon

We present a multifunctional darkfield microscopy using an axicon. It combines the functions of a darkfield microscope, fluorescence microscope, and microspectrophotometer in one platform. The advantage of the system over conventional darkfield microscopy includes the high transmittance of the illuminating flux, the high contrast of the image, and the convenient toggle between darkfield and brightfield microscopy. Examples of dark, bright, and fluorescent micrographs as well as concerned spectra of microsized specimens implemented in this apparatus are demonstrated. (C) 2008 Society of Photo-Optical Instrumentation Engineers.

Fluorescence Hydrogen Peroxide Probe Based on a Microstructured Polymer Optical Fiber Modified with a Titanium Dioxide Film

A highly sensitive microstructured polymer optical fiber (MPOF) probe for hydrogen peroxide was made by forming a rhodamine 6G-doped titanium dioxide film on the side walls of array holes in an MPOF. It was found that hydrogen peroxide only has a response to the MPOF probe in a certain concentration of potassium iodide in sulfuric acid solution. The calibration graph of fluorescence intensity versus hydrogen peroxide concentration is linear in the range of 1.6 x 10(-7) mol/L to 9.6 x 10(-5) mol/L. The method, with high sensitivity and a wide linear range, has been applied to the determination of trace amounts of hydrogen peroxide in a few real samples, such as rain water and contact lens disinfectant, with satisfactory results.

Detection of Copper Ion with Laser-Induced Fluorescence in A Capillary Electrophoresis Microchip

A capillary electrophoresis microchip coupled with a confocal laser-induced fluorescence (LIF) detector was successfully constructed for the analysis of trace amounts of heavy metals in environmental sources. A new fluorescence dye, RBPhOH, synthesized from rhodamine B, was utilized in a glass microchip to selectively determine copper with high sensitivity. A series of factors including running buffer concentration, detection voltage, and sample loading time were optimized for maximum LIF detector response and, hence, method sensitivity.