Absorption color and spatial structure of lead monoxide nanoparticles

Abstract

The results of theoretical modeling of the spatial structure and electronic absorption spectra of isolated small particles of polymorphic modifications of lead monoxide - litharge and massicot, which are characterized by the presence of hypercoordinated atoms, have been analyzed. The optical properties of many oligomers of lead oxide are systematically considered in the work. The results of quantum chemical calculations by the methods of electron density functional theory (DFT and TDDFT) on the spatial structure and energy characteristics, as well as the electronic absorption spectra of the considered models, are discussed. Theoretical results are compared with available experimental data. The calculation method used and the proposed cluster models with or without attached (chemisorbed) water molecules allow us to reproduce the spatial structure and energy characteristics of polymorphic modifications of lead oxide at a semi-quantitative level. It has been found that the addition of water molecules to models for α-lead oxide nanoparticles contributes to their stabilization. The calculated values of the cohesion energy for litharge nanoparticles are greater than those for massicot ones, which corresponds to the experimental data for lead monoxide crystals. The calculated electronic spectra of the litharge nanoparticle models are characterized by absorption bands which lie in the region that corresponds to the red color, and those of massicot relate to yellow; the corresponding values of the width of the energy gap for the litharge models are smaller than for the massicot ones, which is consistent with the experimental data for crystals. The results of calculations show that the presence of hydroxyl groups in nanoparticle models leads to a hypsochromic shift of absorption maxima, so that with a sufficient number of such groups, these species may lose their color.