• S Bhushan

      Articles written in Pramana – Journal of Physics

    • Photo and electroluminescence of ZnO : Er and ZnO : Ag, Er electroluminors

      S Bhushan M Saleem S Chandra

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      A number of ZnO : Er and ZnO : Ag, Er electroluminors have been prepared and their photo (PL) and electroluminescent (EL) properties investigated. While the addition of Ag slightly shifts the PL spectra towards longer wavelength side, the EL spectra not only shift but consist of some new transitions. In ZnO : Er electroluminors, additional transitions also exist at higher frequencies of excitations. Brightness waves for this system consist of two secondary peaks during each half cycle of exciting field. Temperature dependence shows two broad peaks. While voltage dependence of ZnO : Er satisfies the relationB=B0 exp(−b/V1/2), the relationB=B0V exp(−b/V1/2) is found to be suitable for ZnO : Ag, Er electroluminor. Possible mechanisms for these phenomena have been proposed.

    • Some optical properties of rare earth (Dy, Nd and Sm) activated ZnO phosphors

      S Bhushan Balakrishna Rao Kaza A N Pandey

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      Some rare earth (Dy, Nd and Sm) doped ZnO electroluminors have been prepared in vacuum (1 torr) and their photo (PL) and electroluminescence (EL) spectra investigated at room temperature at different concentrations of rare earth (RE) ions. Compared to the spectra of undoped ZnO, these spectra consist of the same bands shifted either towards low or high energy side and the intensity of high energy band is decreased while that of low energy band is enhanced. In any case no additional band or line was observed. The experimental results have been explained on the basis of donor-acceptor pair model of recombination process where donor levels are due to RE ions and the acceptors are the luminescent centres of undoped ZnO electroluminors. The mechanism of excitation is of acceleration-collision type.

    • Brightness waves of electroluminescence in ZnO:Nd electroluminor

      S Bhushan Balakrishna Rao Kaza A N Pandey

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      Brightness waves due to sinusoidal excitations for ZnO:Nd electroluminor have been investigated for a temperature range 93°K to 363°K. During each cycle of excitation it consists of two primary waves each associated with a secondary wave, which grow and disappear twice in this temperature range. These results have been discussed in terms of existing models.

    • Preparation of ZnO phosphors by a new technique

      S Bhushan R P Asare

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      Photo and electroluminescent properties of ZnO phosphors prepared by burning zinc in an atmosphere of pure oxygen have been reported. The peak positions obtained by resolving the experimental curves into Gaussian profiles are explained by assuming that the rare earths form the donor levels while the acceptor levels cause the emission of undoped phosphors. Voltage dependence of electroluminescent brightness shows that the mechanism of excitation consists of acceleration-collision. Brightness waves at different concentrations of rare earths and frequency of excitation are also studied and discussed.

    • ac anddc electroluminescence in CaS:Cu, Sm phosphors

      S Bhushan F S Chandra

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      Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B0 exp (−b/V1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.

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