Investigating charge accumulation mechanisms in organic materials via slow transient emission spectroscopy

Long-persistent luminescent (LPL) materials store photon energy as charges and emit light over extended periods via charge recombination. LPL decay typically follows a power law rather than an exponential decay, enabling confirmation of charge accumulation from emission decay characteristics. While charge generation in organic materials has been widely studied at donor-acceptor (D/A) interfaces, it remains underexplored in single-component luminescent materials. Here, we investigate charge generation in organic solids by dispersing a luminescent molecule in various hosts and performing slow transient emission analyses. This approach enables the evaluation of ionization through accumulated triplet excited states and the detection of weak charge accumulation, which are difficult to capture using conventional transient techniques. Our results show that ionization in single-component materials proceeds through resonance-enhanced multiphoton ionization, although it is less efficient than at D/A interfaces. This approach provides insight into long-term photophysical and photochemical processes such as photodegradation.