Effective synthesis of green nano‐sized ceramic pigments by co‐doping Zn ²⁺ , Cr ³⁺ and Sm ³⁺ into the cobalt‐aluminate

Abstract A green nano‐sized ceramic pigment Co _0.6 Zn _0.4 Al _0.8 Cr _{1.2‐ x} Sm _x O ₄ has been successfully prepared by doping ions Zn ²⁺ , Cr ³⁺ , and Sm ³⁺ into the crystalline CoAl ₂ O ₄ spinel and using the complex‐gel method along with agar as complexing and combustion agent. The Infrared Spectroscopy, X‐ray diffraction, Thermo‐gravimeter, High resolution transmission electron microscopy, Automatic color reader, and UV Vis diffuse reflectance were applied to characterize the pigment power and its gel precursor. The results reveal that the introduction of Zn ²⁺ , Cr ³⁺ , and Sm ³⁺ could change the occupation status of ions in the tetrahedral and octahedral framework of CoAl ₂ O ₄ spinel, leading to the colorant variation of the blue cobalt pigment CoAl ₂ O ₄ , With increasing the content of Sm ³⁺ ion, the reflection peak position of the pigments in visible spectrum appeared a red‐shift, ie the color transition from blue green to yellow green, and the average reflectivity in the violet region decreased to 13.31%, and the band gap energy also changed from 3.47 to 3.20 eV. This illustrates the better UV absorption of this green pigment and can be used as UV shielding material. With the hydrochloric acid or sodium hydroxide solution treatment, this pigment was found to be durable in chemical stability.