Comment on: A significant enhancement in visible-light photodetection properties of chemical spray pyrolysis fabricated CdS thin films by novel Eu doping concentrations [Sens. Actuator. A Phys. 301 (2020) 111749]

In a recent paper [Sens. Actuator. A Phys. 301 (2020) 111749] Shkir et al. have studied the structural, optical and photo-electrical properties of the CdS thin films as a function of Eu doping concentration. The authors have used a wrong equation to calculate the refractive index and obtained values are incorrect. Consequently, the optical properties obtained based on the refractive index such as real and imaginary parts of dielectric constant, dielectric loss, optical conductivity, nonlinear refractive index (n2), linear and third-order non-linear optical susceptibility are wrong.