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The energy band gap of Zn 0.75 Cd 0.25 S 1− z Se z ( x = 0, 0.25, 0.5, 0.75 and 1.0) quaternary alloys have been calculated by using the full-potential linearized augmented plane wave (FPLAPW) method and the Tran–Blaha modified Becke–Johnson (TBmBJ) potential. The lattice volume was first relaxed within the generalized gradient approximation (GGA). The obtained values of the band gaps are found to decrease linearly from 3.61 eV down to 2.83 eV as the content of the Se ion increases in the lattice. These values are in agreement with those reported experimentally for some of ZnS and ZnSe structures. The energies of the interband transitions were determined from the dielectric functions. It is seen that the main interband transitions peaks obtained after the TBmBJ potential is comparable with some reported experimental data. These finding supports the use of the TBmBJ potential as an accurate method in obtaining the energy band gap and the optical constants of semiconductors. [ABSTRACT FROM AUTHOR]

Abstract: Blends made of poly[2-methyl-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conducting polymer and cresyl violet 670 (CV) and coumarin 460 (C460) have been utilized for preparation of organic Schottky diodes. The I–V characteristics of these diodes are then determined and interpreted in terms of thermoionic emission (TIE) conduction process. Upon blending MEH-PPV with CV and C460 dyes, the conduction is seen to completely be through TIE conduction. The turn on voltage for MEH-PPV diode is found to be 2.0V and decreases with CV blending in contrast to the blend of MEH-PPV-C460. The Schottky parameters are determined where the potential barrier is found to be around 0.75V which is consistent with reported values. The charge densities of the respective blends are calculated and found to reduce by in MEH-PPV-C460 blends while it has been enhanced in the CV samples by an order of magnitude compared that of MEH-PPV. The correlation between the ideality factor with the dielectric constant and the charge density is inspected. It is found that the ratio between the charge density of the polymeric blend and the charge density of the Al-electrode is crucial for obtaining low ideality factor. [Copyright &y& Elsevier]

In this work, the spectral, and morphological properties of a conjugated polymer poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with Cresyl Violet (CV) in thin films have been studied. First, MEH-PPV was dissolved in benzene for different concentrations. The solutions were then deposited on glass substrates as thin films using spin coating with thicknesses ranging from 0.85 to 1.40 μm. The photoluminescence (PL) spectrum for the thickness 0.85 μm showed dominated peak at 572 nm and at 615 nm as shoulder peak. By increasing the thickness, the intensity of the peak at 572 nm decreased and the intensity of the peak at 611 nm increased. At a thickness of 1.40 μm there was only one peak at 615 nm and the peak at 572 nm was almost vanished. In general, absorption spectra indicate no aggregation in these films as no new peaks appears by changing the thickness. The morphology of the spin coated conjugated polymer MEH-PPV thin films was measured using Atomic Force Microscopy (AFM). All films examined by AFM, showed a dense structure with average roughness of 7–14 nm. Finally, we reported results of a single layer structure LED with MEH-PPV: CV blend as an active organic layer. The current–voltage ( I – V ) characteristics of these diodes were determined. By blending MEH-PPV with CV dye, we found that the turn on voltage for MEH-PPV diode is 2.0 V and decreases with CV blending. [ABSTRACT FROM AUTHOR]