Herein, triplet–triplet annihilation upconversion (TTA-UC) from near-infrared (NIR, 785 nm) to visible (yellow, centered at 570 nm) regions has been demonstrated in the binary solid of condensed chromophores. Microparticles of the binary solid comprising rubrene as a matrix (emitter) and π-extended Pd-porphyrin as a dopant (sensitizer) in a mole ratio of 1000:1 were obtained by solution casting. Excitation intensity dependence and quantum yield (QY) of the upconverted emission were characterized for individual particles under a microscope and revealed a low threshold intensity (∼100 mW/cm2) as compared to the solution and moderate UC-QY (∼0.5%) in the NIR range. The factors contributing to the UC-QY were investigated by time-resolved and steady-state spectroscopies. It was found that the intersystem crossing of the sensitizer, triplet energy transfer, and TTA occurred efficiently in the binary solid, and the fluorescence QY of the emitter governed the UC-QY.

Peropyrene is a promising candidate molecule for use in organic solar cells based on singlet fission, because it fulfills the energy matching requirement for singlet fission. We prepare three 2,9-disubstitued peropyrene derivatives and investigate their crystal structures, photophysical properties, and singlet fission phenomenon. Although each derivative shows different molecular overlap motifs in solid state, no singlet fission occurs under normal exciton density conditions due to the substantial stabilization of the first excited singlet (S1) state. In contrast, under high exciton density conditions, singlet fission from highly excited singlet (Sn) states, which is generated by singlet–singlet exciton annihilation, takes place to produce a triplet exciton. We also investigate the reverse process of singlet fission, that is, triplet–triplet annihilation, of peropyrene in solution state to explore the possibility of photon upconversion.

Photon upconversion and the triplet energy transfer dynamics were studied for sensitizer-fixed nanoporous glass immersed in emitter solution.

We demonstrated a widely tunable 1-μm optical vortex laser formed from a 0.532-μm optical vortex pumpedoptical parametric oscillator with a singly-resonant cavity configuration employing cascaded non-critical phase-matching LiB₃O₅ crystals. With this system, the topological charge of the pump beam can be selectively transferred to the signal or idler output, and a vortex output in the wavelength range of 850-990 nmor 1130-1300 nm could be obtained.A maximum signal vortex output energy of 0.9 mJ was achieved, corresponding to an optical efficiency of 10%.