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In this paper we report the design of high room temperature photoluminescence internal efficiency InGaN-based quantum well structures emitting in the near ultraviolet at 380 nm. To counter the effects of nonradiative recombination the quantum wells were designed to have a large indium fraction, high barriers, and a small quantum well thickness. To minimize the interwell and interbarrier thickness fluctuations we used Al0.2In0.005Ga0.795N barriers, where the inclusion of the small fraction of indium was found to lead to fewer structural defects and a reduction in the layer thickness fluctuations. This approach has led us to achieve, for an In0.08Ga0.92N/Al0.2In0.005Ga0.795N multiple quantum well structure with a well width of 1.5 nm, a photoluminescence internal efficiency of 67% for peak emission at 382 nm at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the optical properties of a series of InGaN/AlInGaN 10-period multiple quantum wells (MQW) with differing well thickness grown by metal-organic vapor-phase epitaxy that emit at around 380nm. The aim of this investigation was to optimise the room temperature internal quantum efficiency, thus the quantum well (QW) thicknesses were accordingly chosen so that the overlap of the electron/hole wave function was maximised. At low temperature, we observed a reduction of the photoluminescence decay time with decreasing well width in line with the theoretical predictions. For a structure with well thicknesses of 1.5nm, we measured a photoluminescence internal quantum efficiency of 67% at room temperature with a peak emission wavelength of 382nm. [Copyright &y& Elsevier]

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N′-bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)) zinc-pyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular π–π stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via π–π stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9  ×  6.9  Å) formed through intermolecular π–π stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454  nm, and 480  nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred π–π* transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands. [ABSTRACT FROM AUTHOR]

A strong and stable ultraviolet photoluminescence (PL) band (370 nm) together with a red luminescence band around 670 nm with a 730 nm shoulder were observed in Mn-passivated porous silicon (PS) prepared by the hydrothermal technique. The surface structure is examined by Fourier infrared and x-ray photoelectron spectroscopy analysis. The 670 nm band was confirmed to be the usually observed PL band in PS, and the appearance of the 370 nm band and 730 nm shoulder peak was interpreted based on surface structure characterization and spectroscopy measurements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A WO3/TiO2 composite film was in-situ prepared in tungstate electrolyte and characterized by Electron microscopy, X-ray diffraction, UV–Vis spectrophotometer and Photoluminescence. The oxide film consists of mixture phases of anatase and rutile, showing porous structures and metallurgical bond with substrate. With the incorporation of WO3 into TiO2, the optical absorption edge of TiO2 film was shifted to longer wavelength slightly and the separation between electrons and holes was promoted effectively. WO3/TiO2 composite film with increased photo quantum efficiency will be promising in the treatment of environmental pollutants. [ABSTRACT FROM AUTHOR]