Browsing by Author "Kumar, Jitendra"

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    Defect and adsorbate induced ferromagnetic spin-order in magnesium oxide nanocrystallites
    Kumar, Ashok; Kumar, Jitendra; Priya, Shashank (AIP Publishing, 2012-05-01)
    We report the correlation between d(0) ferromagnetism, photoluminescence (PL), and adsorbed hydrogen (H-) species in magnesium oxide (MgO) nanocrystallites. Our study suggests that the oxygen vacancies, namely singly ionized anionic vacancies (F+) and dimers (F-2(2+)) induce characteristic photoluminescence and the room-temperature ferromagnetic spin-order. Nanocrystallites with low population of oxygen vacancies have revealed diamagnetic behavior. Intriguingly, on adsorption of hydrogen (H-) species in the MgO nanocrystallites, ferromagnetic behavior was either enhanced (in the case of highly oxygen deficient nanocrystallites) or begun to percolate (in the case of nanocrystallite with low population density of oxygen vacancies). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712058]
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    Synthesis and Optical Characterization of Mg1-xNixO Nanostructures
    Budiredla, Nageswararao; Kumar, Ashok; Thota, Subhash; Kumar, Jitendra (Hindawi, 2012-11-20)
    An attempt has been made here to synthesize nano-powders via sol-gel process. These powders are shown to possess an f.c.c. (NaCl-type) structure with a typical lattice parameter of  Å for when decomposition of dried oxalate gel product is carried out at 600°C for 2 h in air. Moreover, they exhibit (i) clusters/agglomerates of nanosize particles and (ii) high BET specific surface area (123.0–135.5 m2/g). Also, the infrared absorption spectra reveal their strong affinity to water. The UV-Vis absorption peaks appearing at ~202 nm, 296 nm, and 379 nm are associated with oxygen defect centres and correspond to the electronic transitions (i) (, , or ), (ii) (, or ) and (iii) (), respectively. The incorporation of Ni2+ ions causes some modifications in the energy levels and the optical absorbance characteristics. The suppression of a strong broad emission peak at 440 nm and improvement of a weak band at 400 nm in the photoluminescence (PL) spectrum arise due to decrease in population density of centres (or F+ dimmers) and emergence of additional F+ centres, respectively with increase in nickel content.