A new route for the preparation of CoAl₂O₄ nanoblue pigments with high uniformity and its optical properties

Gamma-ray irradiation assisted polyacrylamide gel route was used to prepare CoAl₂O₄ nanoblue pigments. In this route, citric acid was used as a carboxyl and hydroxyl type chelating agent. The phase purity, morphology, and optical and fluorescence properties of as-prepared samples were analyzed via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometer, transmission electron microscopy (TEM), UV–Visible spectrophotometer, and a confocal Raman system. XRD analysis indicates that the xerogel sintered at relatively low temperature (500 °C) to obtain single phase CoAl₂O₄ nanopowders. The primary crystal of CoAl₂O₄ nanoblue pigment is only 28 nm characterized by TEM, which is more likely to be realized with high uniformity than that the CoAl₂O₄ nanopowders prepared by conventional polyacrylamide gel route. Optical properties of CoAl₂O₄ nanoblue pigment shows that the optical energy gap (Eg) of nanoblue pigment increases with the decrease of crystallite size. The CIE parameter of CoAl₂O₄ nanoblue pigment indicates that a different sintering temperature causes a variation in the color of nanoparticles. The fluorescence spectra show that a major blue emission band around 400 nm and a weaker side band located at 430 nm are observed when the excitation wavelength is 325 nm. The chelation mechanism and fluorescence mechanism of the CoAl₂O₄ nanoblue pigment have been analyzed based on the experimental results.