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.

    • Einstein A-coefficients for rotational transitions in the HN2O+

      S Chandra A K Sharma

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      EinsteinA-values for the electric dipole transitions between the rotational levels up to 540 cm−1 andJ=11 in the ground vibrational state of the protonated N2O (i.e., HN2O+) are calculated. The coefficients are used to compute the mean radiative lifetimes of the levels. TheseA-values can be used for analysing the spectra from astronomical objects, if observed.

    • Two-stream plasma instability as a potential mechanism for particle escape from the Venusian ionosphere


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      In this work, we investigate the possibility of two-stream instability in the Venusian atmosphere leading to momentum transfer, then to the subsequent escape of hydrogen and oxygen ions from the ionosphere.We employthe hydrodynamic model and obtain the linear dispersion relation from which the two-stream instability is studied. Further, the interaction of solar wind with the ions of Venus ionosphere from which the instability sets in, has beenstudied using the data from ASPERA-4 of Venus express. The data support the fact that the two-stream instability can provide sufficient energy to accelerate ions to escape velocity of the planet and thus leave the Venusian ionosphere.

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