Microstructural, optical and magnetic properties study of nanocrystalline MgO

Nanocrystalline MgO is prepared by precipitation method. It has a crystallite size of 13 nm. The particles are agglomerated with varied size ranges. N₂ adsorption–desorption isotherm confirms the mesoporous structure of MgO nanoparticles with a surface area of 145 m² g⁻¹. MgO contains hydride related impurities as evidenced from the Fourier transform infrared (FTIR) spectroscopy results. The UV-vis absorption spectrum of MgO contains several visible absorption peaks mostly associated with oxygen vacancies. These oxygen vacancies trap electrons and form color centers such as F, F ⁺, F ²⁺, F ₂ ²⁺, etc. Photoluminescence (PL) and photoluminescence excitation (PLE) results have revealed that the UV and visible emission peaks of MgO result from these color centers. MgO also exhibits room temperature ferromagnetism. Vacuum annealing, however, reduces the magnetization. Thus, the observed magnetism may not be associated with oxygen vacancies. It is the Mg vacancy which is most likely promoting ferromagnetism in nanoscale MgO. (papers)