UV absorption and effects of local atomic disordering in the nickel oxide nanoparticles

The results of the investigation of optical absorption temperature behaviour for the NiO nanoparticles with sizes 25 and 10 nm are first presented. The spectral dependences of the NiO absorption coefficient in the near UV region are found to obey the Urbach rule. On the basis on independence and additivity of the static and dynamic disorders the information about energy and vibrational structures of nanoparticles is obtained. The fundamental parameters such as energy gap, optical vibrational modes, Debye temperature, deformation potential constant, strength of the exciton-phonon coupling, mean-square atomic displacement of the nanoscaled nickel oxide are determined in terms of the Cody's and Wasim's models. The role of the structural disorder and the size effect on the optical properties of nanoparticles is discussed.Based on the described approach it was established that the dynamic atomic displacements is dominant in the common structural disorder, however the decreasing of size leads to the increasing of static component. In addition there is a simultaneous growth of the energy gap for direct optical transitions and strength of the electron-phonon coupling. It was found that the characteristic feature of small NiO nanoparticles is participation of surface optical vibrational modes in the formation of optical absorption edge.

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