Synthesis, Characterization and Optical Behavior of Nanocrystalline CoWO4

Nanocrystalline CoWO4 sampled were synthesized using a simple mechanochemical approach and a solid-state reaction, respectively. The formation of nanocrystalline CoWO4 was characterized by X-ray diffraction (XRD) and infrared spectroscopy (IR). The optical properties of the obtained samples were explored by diffuse reflectance UV–visible (DRS) and photoluminescence (PL) techniques. A milling speed of 850 rpm led to the direct synthesis of monoclinic CoWO4 with a short reaction time (1 h). The complete reaction did not occur in the solid-state synthesis. The obtained samples had monoclinic crystal systems with different lattice parameters. The average crystallite sizes of CoWO4 were in the range of 20 to 180 nm. The TEM investigation showed that the morphology of the CoWO4 particles differed depending on the preparation conditions. The values of the determined optical bandgap of CoWO4 were the range of 1.89 to 2.18 eV, according to diffusion reflectance spectroscopy in the ultraviolet-to-visible range. Broader blue–green emission spectra with peaks at 430 nm were observed for samples prepared via both routes. The CIE color coordinates of the CoWO4 samples lay in the blue and purple regions. The quantum yields of the CoWO4 samples synthesized after 1 h and 5 h milling times at 850 rom were 0.34 and 0.67%, respectively. This study proposes an affordable mechanochemical approach for blue–green phosphors that could possibly be used in various light-emitting diodes (LEDs).