We report here the optical, photoluminescence (PL), and dielectric properties of Cd_0.40Ni_0.60ZnO₂ nanocomposites annealed between 200 and 600 °C. An increase in annealing temperature (T_ann) up to 600 °C correlates with a gradual increase in the crystallite and particle sizes. The surface area, pore radius, and pore volume are increased as T_ann increases from 200 °C to 300 °C, and then decreased, but still higher than of 200 °C. Similar behaviors were obtained for the absorbance carrier density, photocatlytic efficiency, degradation rate, PL intensity, dielectric constant, dielectric loss, ac conductivity, F-factor, series resistance, and electronic polarizability. While the energy gap, binding energy, impedance of grains and their boundaries, and effective capacitance show an opposite behavior. The relaxation times at the peak of dielectric parameters are between 11.54 and 159.24 ns and between 35.23 and 24273.73 ns, respectively. The Cole-Cole plot shows a single semicircle at T_ann < 400 °C and two successive semicircles at T_ann > 500 °C. The energy of PL °f visible emissions is independent on the chosen T_ann. These findings indicated that the nanocomposite annealed at 300 °C can be used for water purification, telecommunications, solar cells, supercapacitor, and white light-emitting diodes (LEDs).