Unveiling the emission mechanism in analog-doped carbazole-based organic afterglow materials

Abstract

Afterglow from purely organic solids has drawn increasing attention over the past decade. In carbazole-based systems, recent studies revised earlier aggregation-state explanations and implicated trace carbazole analog impurities as the origin. However, the widely assumed charge-trapping mechanism cannot account for exponential decay kinetics, lacks robust experimental validation and leaves some photophysical features unexplained. Here we establish the mechanism by revisiting two representative series of carbazole–analog host–guest systems. Quantitative spectral decomposition and comparative photophysics reveal that the afterglow is dominated by guest phosphorescence, accompanied by an extremely weak power-law long-persistent luminescence. The analog guests are confirmed to act as deep triplet exciton traps and shallow hole traps, the latter of which can enhance hole-transport-type long-persistent luminescence. These insights clarify previously unresolved mechanisms and establish a unified framework for luminescence that integrates energy transfer, exciton diffusion, and three afterglow pathways (delayed fluorescence, room-temperature phosphorescence and long-persistent luminescence), offering design principles for brighter and more persistent purely organic afterglow materials.