Synthesis and Optical Characterization of Mg1-xNixO Nanostructures

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 ？？ 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. 1. Introduction Magnesium oxide (MgO) exhibits an f.c.c. (NaCl-type) crystal structure, high thermal stability, predominantly ionic nature, and insulating behaviour [1]. MgO has been extensively used in catalysis, toxic waste remediation, antibacterial materials, refractories, paints, and superconductors due to its unique optical, electronic, magnetic, thermal, mechanical, and chemical properties [2–8]. Recently, it has found promising application in plasma display panels [9]. Of particular interest is MgO nanopowder because of inherent size effects, for example, large surface area-to-volume ratio [10]. Various investigations have been undertaken earlier on its optical and electrical properties [2, 8, 11]. Surface anions with low coordination, considered to be chemically active sites, form excitons and give rise to specific optical transitions in the UV range [5, 8]. The processes usually used to synthesize MgO nanopowders include thermal evaporation, flame spray pyrolysis, laser vaporization, chemical gas phase deposition, combustion, aqueous wet chemical, vapor-phase transport, sol-gel, and hydrothermal reaction [5, 8, 12–15]. The incorporation of another element into a parent phase (i.e., oxide matrix) leads to crystal defects (e.g., vacancies, interstitials, and antisites) which, in turn, can modify the useful characteristics [16, 17]. Recently, interest arose in transition metal and rare earth-doped oxides mainly due to their excellent luminescence