Cobalt doping effects on photoluminescence, Raman scattering, crystal structure, and magnetic and piezoelectric properties in ZnO single crystals grown from molten hydrous LiOH and NaOH solutions

Transparent, olive-green single-crystal Zn1- xCoxO in the form of hexagonal lamellae grown from molten hydrous LiOH and NaOH solutions have been studied in terms of crystal structure, optical properties, Raman scattering, and magnetic and piezoelectric properties. Rietveld refinement shows that the lattice parameters and bond lengths decrease with increasing cobalt concentration. Cobalt doping results in slight changes to the piezoelectricity of ZnO, but leads to two new photoluminescence emission peaks at wavelengths of 443 and approx. 510 nm, along with the disappearance of certain Raman active modes. Furthermore, the ferromagnetic state is absent in all Zn1- xCoxO crystals, and they are all typically paramagnetic instead.