Novel yellow solid-state fluorescent-emitting carbon dots with high quantum yield for white light-emitting diodes.

Fluorescence quenching of carbon dots (CDs) occurs in their aggregated state ascribed to direct π-π interactions or excessive resonance energy transfer (RET). Thus, CDs have been severely restricted for applications requiring phosphors that emit in the solid state, such as the fabrication of white light-emitting diodes (WLEDs). In this report, novel CDs with bright solid-state fluorescence (SSF) were synthesized by simple microwave-assisted synthesis method, using 1,4,7,10-tetraazacyclododecane (cyclen) and citric acid as precursors. Under 365 nm UV light, these CDs emit bright yellow SSF, indicating they successfully overcome the aggregation-induced fluorescence quenching (ACQ) effect. When the excitation wavelength (λex) is fixed at 450 nm, the emission peak of the CDs is centered at 546 nm with the Commission Internationale de l'Eclairage chromaticity (CIE) coordinates of (0.43, 0.55), which means that they can be combined with a blue-emitting chip in order to fabricate WLEDs. More importantly, the absolute quantum yield (QY) of these CDs powder reached 48% at λex of 450 nm, which was much higher than many previously reported SSF-emitting CDs and indicating their high light conversion ability in solid-state. Thanks to the excellent optical property of these CDs powder, they were successfully used in the preparation of high-performance WLEDs. This study not only enriches SSF-emitting CD-based nanomaterials with good prospects for application, but also provides valuable reference for subsequent research on the synthesis of solid-state fluorescent CDs.