N. T. Q. Hoa, L. T. Hung, N. T. Minh, L. T. K. Nga, and N. H. Quang, “Microstructure and Optical Properties of Transition Metal \(\text{(Co, Ni)}\)-Doped \(\text{TiO}_2\) Nanowires Synthesized by Solvothermal Method”, Comm. Phys., vol. 22, no. 3, p. 247, Oct. 2012.