• T N Misra

      Articles written in Bulletin of Materials Science

    • Spectroscopic, dark and photoconductive properties of some polyene-iodine charge-transfer complexes

      Dilip Ghosh Susmita Hazra Prabir Pal T N Misra

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      Spectroscopic evidence has been provided to confirm that zeaxanthin, lutein and fucoxanthin form molecular charge-transfer (CT) complexes with iodine in the solid state. The semiconductive and photoconductive properties of CT complexes have been investigated in polycrystals in a sandwich cell configuration. Both dark and photoconductivity increases by several orders of magnitude on complex formation. The identical values of thermal activation energies for dark and photoconduction have been obtained for the complexes and this has been attributed to spontaneous carrier generation by CT interaction and their migration by trapping and detrapping mechanisms. Photoconduction action spectra in pure polyene and in polyene-iodine complex suggest that photoinjection from the electrode and direct electron hole pair production are the two photocarrier generation mechanisms operative in these crystals. The second mechanism predominates in pure materials whereas the first one becomes important in the complexes.

    • Electrical properties of naphthyl polyenes

      Seema Sen Prabir Pal T N Misra

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      Dark and photoconductive properties ofα-ω-di-2-naphthyl polyenes were studied at different applied voltages and temperatures. These studies indicate that a single dominant trapping level is involved in both conduction processes. From this study some transport parameters are evaluated. Dependence of photocurrent on excitation light intensity indicates that the carrier generation process is a one-photon process and is trap-limited. The photocurrent decay study indicates that most of the photocarriers decay exponentially with time. Trap depths are calculated from the temperature dependence of decay constant and is found to be the same as that obtained from thermally stimulated current. The dependence of photocurrent on wavelength indicates two mechanisms of photocarrier generation process: one is excitonic and the other is intrinsic electron-hole pair production.

    • Studies of photoconductivity in β-Apo-8′ carotenal

      Seema Sen T N Misra

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      The photoconductive properties of a carotenoid polyene,β-Apo-8′ carotenal in polycrystalline form has been studied. The growth of the photocurrent shows an overshoot in the growth-time curve before steady state value is attained. This behaviour of photocurrent is proposed to be due to higher value of recombination coefficient than trapping coefficient. From the temperature dependence study it is observed that the steady state photocurrent, at first increases with increase of temperature, attains a maximum at a particular temperatureTmax and then decreases with temperature. TheTmax value agrees with the temperature above and below which steady state photocurrent is attained differently. Monomolecular and bimolecular recombination processes at two temperature regimes are proposed to account for the observed behaviour. The dependence of photocurrent with excitation light intensity and wavelength study provide information on the carrier generation processes. The fast decay of photocurrent have been observed at different temperatures and from this study the decay constant is calculated and it is found to be temperature independent.

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