• C P G Vallabhan

      Articles written in Bulletin of Materials Science

    • Effects of insulating layer on the performance of thin film electroluminescent devices

      M K Jayaraj C P G Vallabhan

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      Thin film electroluminescent devices were fabricated with active layer of ZnS:Mn and different insulators viz Sm2O3, Eu2O3, Na3A1F6, MgF2, CeO2 and SiO in MIS and MISIM structure. The threshold voltage for light emission in AC thin film electroluminescent devices of MIS and MISIM structures is found to depend on the dielectric properties of insulating materials. The observed threshold voltage for these devices and its variations for devices with different insulators are explained using the equivalent circuit for the device and the dielectric properties of the insulting material used for the preparation of device. Variation of threshold voltage with operating time is also studied for some of the devices.

    • Characteristics of laser-induced plasma from highTc superconductor

      G Padmaja A V Ravi Kumar V Vidyalal P Radhakrishnan V P N Nampoori C P G Vallabhan

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      The spectroscopic analysis of the emission from the plasma produced by irradiating a highTc superconducting GdBa2Cu3O7 target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential.

    • Damage threshold determination of bulk polymer samples using pulsed photothermal deflection technique

      K Rajasree A V Ravikumar P Radhakrishnan V P N Nampoori C P G Vallabhan

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      Photothermal deflection technique was used for determining the laser damage threshold of polymer samples of teflon (PTFE) and nylon. The experiment was conducted using a Q-switched Nd-YAG laser operating at its fundamental wavelength (1-06μm, pulse width 10 nS FWHM) as irradiation source and a He-Ne laser as the probe beam, along with a position sensitive detector. The damage threshold values determined by photothermal deflection method were in good agreement with those determined by other methods.

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