Clustering-Induced White Light Emission from Carbonized Polymer Dots

Despite the advancements in synthetic methods, it is still challenging to prepare white light-emitting carbon dots for solid-state white light-emitting diodes (LEDs). Herein, the synthesis and characterization of a carbonized polymer dot (CPD) that emits white light in the solid state are presented. The reaction of an oxygen-rich precursor, trimethylolpropane tri(cyclic carbonate) ether, with nitrogen-rich melamine in an alcohol via a single-step solvothermal method affords CPDs with hydroxyurethane and CN groups. The morphology of the CPDs can be regulated by changing the reaction time. Transmission electron microscopy reveals structural evolution from flocculent polymers to dandelion-like and spherical particles with an increase in the carbonization time from 6 to 12 and 18 h, respectively. The dandelion-like CPDs exhibit a relatively high quantum yield of 7.5% in the solid state, which is ascribed to the abundant surface poly(hydroxyurethane) chains that restrict the aggregation-caused quenching of luminescence. It is proposed that multiple coexistent clusters generate different emission sites, thereby leading to white light emission. Loose clusters formed from hydroxyurethane and CN bonds, which have a low degree of conjugation, emit blue light, whereas compact clusters generated through interactions between the hydroxyurethane and CN bonds of poly(hydroxyurethane) and carbon cores emit yellow light.