The graphene-oxide (GO) nanosheets were synthesized by varying the degree of oxidation levels in which the observation of different domain size (sp2) of GO and their relationship in photoluminescence (PL) characteristics were investigated. GO consists of two unique carbon domains sp2 and sp3, in which each domain have different charge carrier recombination pathway within the domain. As-prepared GO sample shows the broad emission peak ranging from 350 nm to 600 nm. The PL emission has been tuned from blue to yellow and the emission is directly proportional to corresponding size of sp2 cluster. The Gaussian peaks are centered at different wavelength region for various sizes of sp2 cluster. While increasing the degree of oxidation, the concentration of functional groups are found to be increased resulting the enlargement of sp2 domain size from 15.96 nm to 16.28 nm, due to this, the red shift was observed in the emission spectra. Our results show a basic understanding in photoluminescence characteristics of GO with the effect of oxygenated functional groups.