Revealing Charge Accumulation Mechanisms in Organic Materials via Slow Transient Emission Spectroscopy

Long-persistent luminescent (LPL) materials store photon energy as charge and emit light over extended periods due to charge recombination. The LPL decay profiles follow a power-law rather than an exponential decay, enabling the confirmation of charge accumulation from the emission decay characteristics. While charge generation in organic materials has primarily been discussed in the context of photo-induced charge separation at electron donor-acceptor (D/A) interfaces, charge generation in single-component luminescent materials has not been extensively addressed. Here, we investigated the mechanism of charge generation in organic solids by dispersing the same luminescent material in various host media and performing slow transient emission analyses. This approach allowed us to evaluate ionization through accumulated triplet excited states and detect extremely weak charge accumulation, which is challenging with conventional transient analyses.