Magnetic field-driven photoluminescence modulation in graphene oxide quantum dots: Insights into enhancement mechanisms

•Magnetic brightening of graphene oxide quantum dots photoluminescence at low temperature.•The electron-hole exchange interaction generates a splitting between single-bright and triplet-dark states.•A large splitting energy can suppress non-radiative transition, enhancing fluorescence and fluorescence lifetime. The electron-hole exchange interaction governs the exciton dynamics in semiconductor quantum dots, which modulates the photoluminescence (PL) properties in various applications. Generally, the exciton dynamics exhibit significant dependence on temperature and magnetic field. Here, we demonstrate that the electron-hole exchange interaction in graphene oxide quantum dots (GOQDs) is enhanced by magnetic field at low temperatures, resulting in increased PL. Specifically, the exciton states can split into singlet-bright and triplet-dark states due to the strong electron-hole exchange interaction. The bright-dark splitting increases below 30 K and under a magnetic field up to 40 T, which suppresses the non-radiative transitions of triplet-dark state. Therefore, PL intensity and lifetimes also increase below 30 K. This study enriches the understanding of the fundamental magneto-optical properties in carbon-based quantum dots.