Effective mass model supported band gap variation in cobalt-doped ZnO nanoparticles obtained by co-precipitation

Zn$_{1-x}$ Co$_x$ O ($x$ = 0.0, 0.01, 0.03, 0.05) nanoparticles were synthesized using co-precipitation method. Shift in peaks of XRD patterns for 2$\theta$ values has been observed. The changes in 2$\theta$ value for different peaks for different samples are studied systematically. Dislocation densities $(\delta)$ for the samples are calculated and correlated with observed shift in 2$\theta$ values for all the samples. UV-Vis study has been performed to understand the effect of cobalt doping on optical band gap. The band gap shows a cubic variation with dopant concentration $(x)$. The nature of band gap variation has been explained and supported by effective mass model. Samples are also characterized by SEM and EDX to understand the surface morphology and elemental composition.