Efficient dipole-dipole coupling of Mott-Wannier and Frenkel excitons in (Ga,In)N quantum well/polyfluorene semiconductor heterostructures

Journal ArticleWe investigate interactions between Mott-Wannier (MW) and Frenkel excitons in a family of hybrid structures consisting of thin organic (polyfluorene) films placed in close proximity (systematically adjusted by GaN cap layer thickness) to single inorganic [(Ga, In)N/GaN] quantum wells (QWs). Characterization of the QW structures using Rutherford backscattering spectrometry and atomic force microscopy allows direct measurement of the thickness and the morphology of the GaN cap layers. Time-resolved photoluminescence experiments in the 8-75 K temperature range confirm our earlier demonstration that nonradiative energy transfer can occur between inorganic and organic semiconductors. We assign the transfer mechanism to resonant Förster (dipole-dipole) coupling between MW exciton energy donors and Frenkel exciton energy acceptors and at 15 K we find transfer efficiencies of up to 43%. The dependence of the energy transfer rate on the distance R between the inorganic QW donor dipole and organic film acceptor dipole indicates that a plane-plane interaction, characterized by a 1/R2 variation, best describes the situation found in our structures

Optimized production of coal fly ash derived synthetic zeolites for mercury removal from wastewater

Coal fly ash (CFA) derived synthetic zeolites have become popular with recent advances and its ever-expanding range of applications, particularly as an adsorbent for water and gas purification and as a binder or additive in the construction industry and agriculture. Among these applications, perpetual interest has been in utilization of CFA derived synthetic zeolites for removal of heavy metals from wastewater. We herein focus on utilization of locally available CFA for efficient adsorption of mercury from wastewater. To this end, experimental conditions were investigated so that to produce synthetic zeolites from Kazakhstani CFAs with conversion into zeolite up to 78%, which has remarkably high magnetite content. In particular, the effect of synthesis reaction temperature, reaction time, and loading of adsorbent were systematically investigated and optimized. All produced synthetic zeolites and the respective CFAs were characterized using XRD, XRF, PSA and porosimetric instruments to obtain microstructural and mineralogical data. Furthermore, the synthesized zeolites were studied for the removal of mercury from aqueous solutions. A comparison of removal eficiency and its relationship to the physical and chemical properties of the synthetic zeolites were analyzed and interpreted

Zeolite development from fly ASH and utilization in lignite mine-water treatment

The synthetic zeolitic materials were tested comparatively, showing that the more intense the zeolitic presence in the synthetic materials, the greater the uptake rates for certain groups of trace elements

Mineralogical, microstructural and thermal characterization of coal fly ash produced from Kazakhstani power plants

Coal fly ash (CFA) is a waste by-product of coal combustion. Kazakhstan has vast coal deposits and is major consumer of coal and hence produces huge amounts of CFA annually. The government aims to recycle and effectively utilize this waste by-product. Thus, a detailed study of the physical and chemical properties of material is required as the data available in literature is either outdated or not applicable for recently produced CFA samples. The full mineralogical, microstructural and thermal characterization of three types of coal fly ash (CFA) produced in two large Kazakhstani power plants is reported in this work. The properties of CFAs were compared between samples as well as with published values

Analysis of the Transport Process Providing Spin Injection through an Fe/AlGaAs Schottky Barrier

Electron spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single step tunneling is the dominant transport mechanism. The current-voltage data show a clear zero-bias anomaly and phonon signatures corresponding to the GaAs-like and AlAs-like longitudinal-optical phonon modes of the AlGaAs barrier, providing further evidence for tunneling. These results provide experimental confirmation of several theoretical analyses indicating that tunneling enables significant spin injection from a metal into a semiconductor.Comment: 4 pages, 4 figures, submitted to AP