Facile synthesis of highly graphitized nitrogen-doped carbon dots and carbon sheets with solid-state white-light emission

We report the hydrothermal synthesis of nitrogen-doped carbon dots (NCDs) and carbon sheets (NCSs) with glucose and ammonia as precursors. The formation and N-doping of NCSs were one-step obtained. NCSs are highly graphitized with six-fold symmetry single-crystal character. The optical properties of NCDs and their application as single-phase solid-state phosphors toward white light-emitting diodes (LEDs) were thoroughly investigated. NCDs solutions exhibit strong blue-green emission under ultraviolet (UV) light illumination and possess excitation-dependent photoluminescence (PL) behavior. Irradiated by UV LEDs, NCDs solutions show broad PL in visible spectral region. To resist self-quenching of NCDs powder resulting from aggregations, poly (vinyl alcohol) (PVA) was added into NCDs solution. Without adding any other phosphors, solid-state NCDs/PVA composite demonstrates direct white-light emission. Our research offers a valuable reference for growing highly graphitized NCSs by facile hydrothermal method and developing white UV-LEDs with environment-friendly and metal-free NCDs phosphors.