Spectroscopic properties of $$\hbox {Cr}^{3+}$$ Cr 3 + in the spinel solid solution $$\hbox {ZnAl}_{2-x}\hbox {Cr}_{x}\hbox {O}_4$$ ZnAl 2 - x Cr x O 4

Abstract

The evolution of the structural environment of $$\hbox {Cr}{^{3+}}$$ along the solid solution $$\hbox {ZnAl}_{2-x}\hbox {Cr}_{x}\hbox {O}_4$$ has been investigated using a multi-analytical approach. X-ray diffraction confirms that the system follows Vegard’s law. Diffuse reflectance spectra show a decrease of the crystal field parameter with the Cr content, usually related to the increase of the Cr–O bond length in a point charge model. This interpretation is discussed and compared to the data obtained by first-principle calculations based on density functional theory. X-ray absorption near edge structure spectra at the Cr K-edge show a pronounced evolution in the pre-edge with the Cr content, characterised by the appearance of a third feature. Calculations enable to assign the origin of this feature to Cr neighbours. The colour change from pink to brownish pink and eventually green along the solid solution has also been quantified by calculating the L*, a*, b* and x, y coefficients in the system defined by the International Commission on Illumination.