New Insight into Fluorescent Polymeric Carbon Dots for Solid-State Laser Device

Polymeric carbon dots (PCDs) are an astonishing classof fluorescentmaterials with distinctive structures, properties, and applications.However, the internal structures of PCDs are still unclear and arethe subject of considerable debate due to their complexity. Herein,a new type of pure blue light-emitting PCDs was synthesized hydrothermallyfrom & epsilon;-poly-l-lysine and citric acid. PCDs were observedby using scanning transmission electron microscopy coupled with electronenergy loss spectroscopy (STEM-EELS) on an atomically thin graphenesurface to determine the internal structure and compositional gradientscombined with other spectroscopic analyses. These methods revealedthat PCDs have a spongy, porous structure with uniform element distribution,reflecting organic polymeric frameworks that embrace fluorescent aromaticmoieties devoid of graphitic, inorganic carbon. The polymeric frameworkacts as a transparent matrix and effectively resists self-quenchingof photoluminescence (PL) in the solid state. Exploiting their excellentfluorescence properties, PCDs were embedded in a planar microcavitycomposed of two distributed Bragg reflectors (DBR), which was demonstratedas a single longitudinal solid-state blue laser. The results willfacilitate a detailed understanding of internal structures of PCDsand their efficient, solid-state emission toward the development ofrare-earth-free lighting devices. The internalstructure of polymeric carbon dots on atomicallythin graphene and their applicability as microcavity-integrated opticalgain media are reported.