Organic solid-state lasers are essential for various photonic applications, yet current-driven lasing remains a great challenge. Charge transfer (CT) complexes formed with p-/n-type organic semiconductors show great potential in electrically pumped lasers, but it is still difficult to achieve population inversion owing to substantial nonradiative loss from delocalized CT states. Here, we demonstrate the lasing action of CT complexes based on exciton funneling in p-type organic microcrystals with n-type doping. The CT complexes with narrow bandgap were locally formed and surrounded by the hosts with high-lying energy levels, which behave as artificial light-harvesting systems. Excitation light energy captured by the hosts was delivered to the CT complexes, functioning as exciton funnels to benefit lasing actions. The lasing wavelength of such composite microcrystals was further modulated by varying the degree of CT. The results offer a comprehensive understanding of exciton funneling in light-harvesting systems for the development of high-performance organic lasing devices.

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One-dimensional photonic crystal (PC) slabs are capable of enhancing the excitation of fluorescent material adsorbed on their surface. In this report, we demonstrate and verify by electromagnetic computer simulations that resonant leaky modes spectrally overlapping the laser wavelength used for fluorescent excitation are responsible for the enhanced excitation, and that the Q-factor of the PC resonance is proportional to the resonant electric field intensity and thus proportional to the fluorescent enhancement factor. As a demonstration, we have fabricated a single PC slab surface with an intentional spatial gradient in the resonant wavelength and demonstrate enhanced fluorescence only from locations on the PC surface with a leaky mode corresponding to a 633 nm HeNe laser used to excite Cyanine 5 dye deposited uniformly across the PC. The results show that enhanced fluorescence signals for one-dimensional PC slabs originate from increased excitation of the fluorescent dye.