Quynh, Ta Duy, et al. “On the Contribution Factors of Enhanced Photocatalytic Activity of Doped Semiconductors: Structural and Optical Investigation of Cu2+ Doped ZnO Nanoparticles”. Vietnam Journal of Science and Technology, vol. 59, no. 3, May 2021, pp. 277-89, doi:10.15625/2525-2518/59/3/15490.