Optical properties and complex refractive index of Co-doped ZnO waveguide thin films elaborated by spray pyrolysis

$${\text{Co}}_{x}{\text{Zn}}_{1-x}{\text{O}}$$ (x = 0.00, 0.04, 0.08, and 0.10) thin films were sprayed pyrolysis onto ordinary glass substrates. The micro-Raman spectroscopy revealed the presence of wurtzite structure in all films. UV–Vis investigation showed good optical transmittance visible region with increase absorption bands related to internal $${\text{Co}}^{+2}$$ d–d transitions over Co concentration. gap energy decreased by 0.34 eV as doping increased, contrary Urbach which increased 230 meV. SEM observation indicated grain shape modification surface morphology addition slight decrease size. M-lines measured refractive index was found 0.0156 increased. Cobalt provoked extinction light coupling propagation manifested an full width at half maximum guided peaks a reflected intensity. This due coefficient spectroscopy.