Correlated quartic variation of band gap and NBE energy in sol-gel derived Zn1−xCoxO nanoparticles

Zn1−xCoxO (x = 0.0, 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized via sol-gel method. For structural parameters like lattice constants, bond length and particle size, XRD patterns have been analyzed. The particle sizes lie between 15.75 and 35.31 nm. The Williamson-Hall analysis has been performed for strain calculation. The UV–Visible spectra show high transparency in visible range with a dip in near UV region. The band gap calculation has been done using Tauc's plot method. The band gap values show a quartic variation with x. PL emission spectra exhibit NBE emission that too undergoes quartic variation with x. The correlation between both the quartic variations has been analyzed and it has been established that the B-M effect and sp-d exchange interaction both play their role alternately. M-H curves of the Co doped nanoparticles show room temperature ferromagnetism whereas the undoped one have the diamagnetic character. The electrical resistivity has been found to be high; in the range of 4.81 × 104 to 7.26 × 104 Ω-m. A increasing trend in resistivity is noticed with increasing the Co concentration in ZnO matrix. •Zn1−xCoxO (x = 0.0, 0.01, 0.03, 0.05, 0.07) NPs are synthesized via sol-gel method.•Quartic variation in band gap of Zn1-xCoxO nanoparticles has been observed.•NBE emission energy also follows the quartic variation but with opposite nature.•Room temperature ferromagnetism is observed in Co doped ZnO nanoparticles.•An increasing trend in resistivity is noticed with increasing the Co concentration.