Properties of Nanoscale Zn_(1-x)Co_хO Pigments

Purpose of research - characterization of microstructural, optical and electronic properties of synthesized samples of nanosized inorganic pigments of the composition Zn_(1-x)Co_xO (x = 0.02-0.15).

Methods. Inorganic powder pigments with the general formula Zn_(1-x)Co_xO (x = 0.02-0.15) were synthesized by the pyrochemical nitrate-urea method using crystalline hydrates of metal nitrates and urea. The initial reagents in the required stoichiometric ratio were thoroughly mixed with urea powder in a ceramic mortar and then thermolysis of the reaction mixture was carried out in ceramic crucibles with the decomposition of nitrate salts with the formation of colored green powders of varying color intensity. The microstructure of the prepared pigment powders was investigated using a JEOL JSM-7500F scanning electron microscope. The composition of the pigments was studied by energy dispersive microanalysis using an Inca X Sight EDX Spectrometer attachment. Optical diffuse reflectance spectra of synthesized pigment powders were measured on a Hitachi U-3900 spectrophotometer with a two-channel integrating sphere in the wavelength range from 300 to 900 nm.

Results. By means of particle SEM analysis of the synthesized Zn_(1-x)Co_xO pigments, it was taken into account that they are nanopowders with an average nanoparticle size from 20 to 45 nm and with varying degrees of nanoparticle agglomeration. The diffuse reflectance spectra of pigments doped with different amounts of cobalt ions in the wavelength range from 300 to 900 nm show a systematic increase in the intensity of the green color with an increase in the cobalt content. All studied samples of the synthesized pigments Zn_(1-x)Co_xO are semiconducting compounds with several direct-gap electronic transitions.

Conclusion. With an increase in the percentage of cobalt particles in the composition of the investigated green inorganic pigments with the general formula Zn_(1-x)Co_xO a decrease in reflectivity was observed in the entire investigated optical range, and especially in the range from 600 to 680 nm. The difference in color parameters for the studied inorganic oxide pigments of the composition Zn_(1-x)Co_xO is mainly associated with both a change in the fraction of chromogenic cobalt ions in them and a change in the nearest coordination of oxygen atoms in the Co-O_n coordination polyhedron, which affects the parameters of electronic transitions ion Co ⁺. The calculated color parameters in the CIE Lab color space allow you to guide the selection of the composition of Zn_(1-x)Co_xO pigments to achieve the desired color.

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