Solid-state N,P-doped carbon dots conquer aggregation-caused fluorescence quenching and couple with europium metal-organic frameworks toward white light-emitting diodes

As a newly discovered photoluminescent material, carbon dots (CDs) have shown promising performance in many fields. However, due to aggregation-caused fluorescence quenching, most of CDs are poorly emissive in the solid state, which severely restricts their wide applications, especially in the optoelectronic devices. To overcome this problem, herein, we design a novel kind of self-quenching-resistant N,P-doped CDs, using polyethyleneimine (PEI), phosphoric acid, and ethanol as raw ingredients. The as-synthesized CDs are amorphous and contain abundant surface PEI chains which properly separate the individual carbon core and prevent the direct pi-pi interaction. Such a unique structure conquers self-quenching during aggregation, and gives CDs a bright blue fluorescence in solid state without any other additional matrices. By taking advantage of their excellent optical properties, the CD powers, combined with red emissive europium metal-organic frameworks, are successfully employed as hybrid phosphors for construction of white light-emitting diodes exhibiting a Commission Internationale de L'Eclairage (CIE) coordinate of (0.33, 0.33)