Researchers report blue photoluminescence (PL) from solution-processed graphene oxide (GO). The emission arises from recombination of electron-hole pairs in small sp² carbon clusters embedded in an sp³ matrix. This finding suggests that GO can serve as a parent structure for chemically engineered fluorescent components while maintaining macroscopic integrity. The PL intensity increases with reduction treatment, reaching up to 10 times higher than as-synthesized material. Reduction of GO can be achieved through hydrazine vapor exposure, transforming it from an insulator to a semimetal. The PL peak remains around 390 nm despite reduction, with intensity increasing initially but decreasing after prolonged exposure. The blue emission is attributed to localized sp² clusters, which are crucial for radiative recombination. The energy gap between π and π* states in these clusters determines the PL wavelength. The study also shows that GO's optoelectronic properties, including a finite band gap, differ from mechanically exfoliated graphene. The results highlight the potential of GO for solution-processable optoelectronics, with applications in displays, lighting, and bio-sensing. The findings suggest that controlling the sp² fraction and cluster size can tune PL emission, offering a pathway to efficient and tunable blue PL for optoelectronic devices. The research was supported by the NSF CAREE Award and other funding sources.Researchers report blue photoluminescence (PL) from solution-processed graphene oxide (GO). The emission arises from recombination of electron-hole pairs in small sp² carbon clusters embedded in an sp³ matrix. This finding suggests that GO can serve as a parent structure for chemically engineered fluorescent components while maintaining macroscopic integrity. The PL intensity increases with reduction treatment, reaching up to 10 times higher than as-synthesized material. Reduction of GO can be achieved through hydrazine vapor exposure, transforming it from an insulator to a semimetal. The PL peak remains around 390 nm despite reduction, with intensity increasing initially but decreasing after prolonged exposure. The blue emission is attributed to localized sp² clusters, which are crucial for radiative recombination. The energy gap between π and π* states in these clusters determines the PL wavelength. The study also shows that GO's optoelectronic properties, including a finite band gap, differ from mechanically exfoliated graphene. The results highlight the potential of GO for solution-processable optoelectronics, with applications in displays, lighting, and bio-sensing. The findings suggest that controlling the sp² fraction and cluster size can tune PL emission, offering a pathway to efficient and tunable blue PL for optoelectronic devices. The research was supported by the NSF CAREE Award and other funding sources.