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Currently there is a great interest in II–VI semiconductor nanoparticles, particularly organically capped soluble particles of cadmium or zinc sulphide and selenide, for their ready to use application in devices. For electroluminescence (EL) devices, it is expected to cover a broad spectrum and to tune various specific colours by preparing Cd1-xZnx Se instead of CdSe and ZnSe. Ternary alloys have composition dependent properties; therefore Cd1-xZnxSe has attracted much attention in the fields of luminescence and optoelectronic devices. It has wide optical band-gap and good stability with respect to environment. In this study, Cd1-xZnxSenanoparticles have been synthesized by using starch as a capping agent through a chemical synthesis route at room temperature. Samples have been prepared varying composition factor ‘x’ in ternary alloy Cd1-xZnxSe. Cubic structure of all has been confirmed by XRD. Crystallite size calculated from XRD was found in the range of 3-5 nm and it was observed that size reduces on increasing Zn content in ternary compound. Optical absorption spectra showed the blue shift in absorption edge with increasing Zn content. Band gap has been obtained by absorption studies and increase in band gap observed on increasing Zn content in the compound. Electroluminescence studies reveal that lower threshold voltage is required for samples with lower ‘x’ value. The Brightness increases on increasing the voltage above threshold voltage and the variation pattern is almost exponential for all samples. The voltage-current curve represents ohmic nature of the EL cell. Impedance was found to increase on increasing ‘x’ value. The increase in EL intensity is faster for higher frequency. EL spectra revealed that light emission is in violet-green region corresponding to band gap for both Cd0.75 Zn 0.25Se and Cd0.5 Zn 0.5Se, with a slight blue shift on increasing Zn content. A ternary system Cd1–xZnxSe, may be engineered better for application purpose by suitably choosing the composition parameter ‘x’.Contents of Paper

Sulfide based luminescent materials have attracted a lot of attention for a wide range of photo-and electroluminescence applications. Among the sulfides, ZnS is promising host material for development of phosphors in different visible emission bands. Doping of Ag can affect the electroluminescence of the host material. Incorporation of host ZnS into the polymer matrix is one of the best method to display their special functions, which stabilize the nanoparticles. Here we report a synthesis and electroluminescence of silver doped ZnS/PVK nanocomposites thin films. Reported films were prepared by using chemical route with varying Ag doping and ZnS loading in the composite. Structural and morphological characterization were carried out through XRD and SEM techniques, which confirmed the particles in nanoregime. Though optical absorption spectra and band gap of ZnS semiconductor nanoparticles in ZnS:Ag/PVK matrix were estimated, and using EMA model, particle size was calculated which supports the results of XRD. Electroluminescence of nanocomposite samples was studied and it was found that threshold voltage depends on doping of Ag and also on loading of ZnS. Voltage brightness characteristics support the production of EL by acceleration-collision mechanism.Contents of Paper

Several research groups have reported that nanocrystalline II-VI semiconductors show enhanced luminescence, increased oscillator strength and shorter response time. Nanocrystalline powder samples of CdS, CdSe, ZnS and ZnSe nanocrystals and their composites with PVA and PVK have been prepared by chemical route. SEM. TEM and AFM images indicate agglomeration of particles. XRD reveal the crystal structure and size in nanometer range and absorption spectra show increased band gap due to quantum confinement.The EL studies on nanocrystalline powder samples and nanocrystal/polymer composites have shown that the light emission starts at certain threshold voltage, different for different specimens and then increases with increasing voltage. It is found that smaller nanocrystals have lower threshold voltage and higher EL brightness. It is observed that nanocomposite give much higher electroluminescence starting at lower voltage and increasing very fast with the voltage as compared to nanocrystalline powder. The emission spectra are found to depend on the material, crystalline size and doping. Electroluminescence in undoped and doped chalcogenide nanocrystals and nanocomposites is reviewed in this paper. In nanosize regime, electroluminescence (EL) is governed by the size quantization effect. Contents of Paper