Research on lasers using organic materials and soft materials has a very long history, and the contributing to 'immediate realization of ideas for lasers' have been often provided by the organic material process. This“ Special Issue” will introduce innovative researches about organic soft-materials about laser and optoelectronics.

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We report low-threshold organic surface-emitting distributed feedback lasers that operate in a quasi continuous-wave regime at 80 MHz and under 30 ms. The stability of the device was significantly enhanced with the encapsulation of CYTOP, resulted in 3% loss even after 500 pulse shots.

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We proposed the use of light-emitting electrochemical cells (LECs) to demonstrate polymer injection lasers. We demonstrated optically pumped amplified spontaneous emission (ASE) in the active layer of LECs by a blend of a polymer and an ionic liquid. Using ionic liquid enabled the film blend to maintain a high degree of transparency with the flat surface, resulting in film as an optical slab waveguide that achieved a low ASE threshold energy of 4 μJ/cm2. A planar LEC based on the polymer:ionic liquid blend showed a fast turn-on, a bright linear shape emission in the middle of the two contacts, and a high current density over 1 kA/cm2 using a pulse driving technique. Furthermore, the application of short voltage pulses of 200 ns successfully avoided an efficiency roll off, which is a critical issue for laser oscillation by electrical excitation under high current density.

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This paper reports the photophysical properties of E,E-1,4-bis(4-trifluoromethylstyryl)benzene (4CF3) as a benchmark and discuss four other bis-styrylbenzene derivatives (BSDs): E,E-1,4-bis(2- trifluoromethylstyryl)benzene (2CF3), E,E-1,4-bis(3-trifluoromethylstyryl)benzene (3CF3), E,E-1,4- bis(4-cyanostyryl)benzene (4CN), and E,E-1,4-bis(4-nitrostyryl)benzene (4NO2.) The author confirmed the microcrystals of 4CF3 for amplified spontaneous emission. The fluorescence quantum efficiency of 2CF3 in its solid state was much higher than that in its solution, suggesting that 2CF3 showed aggregation-induced emission. The ionization potential values (IPs) of the BSDs were markedly affected by the introduction position of the trifluoromethyl (CF3) group; the IPs of 2CF3, 3CF3, and 4CF3 were ‒5.9 eV, ‒6.7 eV, and ‒6.5 eV, respectively. The IP of 4CF3 was lower than those of 4NO2 and 4CN, meaning the introduction of the CF3 group effectively lowered the IP.

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Microcavity devices using organic luminescent materials are highly promising for the cavity polariton formation and condensate at room temperature. Furthermore the state of cavity polariton might be also helpful to achieve the electrically driven organic laser owing to its half-matter and half-light nature. In this article we review recent progresses of the organic cavity polariton studies including some recent results presented by the authors’group, which are on a highly molecular oriented organic single crystal microcavity.

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We present self-assembled conjugated polymer microspheres that act as whispering gallery mode (WGM) resonators. For the preparation of conjugated polymer microspheres, vapor diffusion and miniemulsion methods are adopted. For the vapor diffusion method to obtain microspheres, amorphous aggregation of the polymers are crucial by introducing sterically bulky moieties that largely twists the polymer main chain. Focused laser irradiation to the perimeter of the microspheres excites WGM, where sharp and periodic lines appear in the PL spectrum. With a benefit of the high light confinement properties, we demonstrate long distance, directional, and efficient light energy transfer and wavelength conversion through bispheres. Furthermore, WGM lasing is achieved from conjugated polymer microspheres upon femtosecond pumping. Conjugated polymer microsphere resonators have advantages of high photoabsorptivity, high refractive index, and inherent conducting properties, as well as the simple fabrication process, which are valuable for applications to optical circuits, electrically-driven lightings, and chemical and biological sensors

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This article describes an overview of the developments in fabrication methodologies of colloidal crystals (CCs) as photonic crystals (PCs) and their laser applications. The CCs have intrinsic capabilities to selfassemble the 3D-PC structure of micro-particles. When the periodic length in the CC structures corresponds to several hundred nanometers of the visible light wavelength, the photonic band-gaps (PBGs) can be visualized as reflection colors according to Bragg’s law. When combining light-emitting organic dyes within the CC structures, the stimulated laser action at PBG wavelength edge or within PBG wavelength range can be generated by optical excitation due to the PBG effect. Moreover, we succeed in the demonstration of flexible and tunable laser action from the CC structures with lightemitting organic dyes. The preset review highlights not only the research backgrounds of CCs as PCs, but also the experimental results of our soft organic CC lasers.

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Horizontally oriented ter (9, 9’-spirobifluorene) (TSBF) based organic light-emitting diodes (OLEDs) were fabricated with the device structure that has no heterointerfaces (anode/n-TSBF/TSBF/p-TSBF/ cathode). Optimizing the doping concentration and the thicknesses of n-and p-doped TSBF layers, we found the possibility to suppress the efficiency roll-off characteristics. These results indicate the potential use of TSBF for realizing organic solid-state lasers.

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We experimentally demonstrated the fabrication and the fundamental lasing evaluation of a microdisk cavity by focusing on a fluorinated spherical polymer (FZ-001) to achieve a microdisk with small absorption loss in the visible range. In a translucency evaluation, FZ-001, which is a host material polymer of the microdisk, shows translucency over about 250 nm on the short wavelength. Transparency on the longer wavelength region over about 320 nm is 99% or more. The polymer concentration of the ink was set as high as 20 wt.%, and sufficient ejection was possible. In the WGM lasing evaluation, we observed a comb-shaped spectrum with a peak near the fluorescence peak wavelength of doped dye pyrromethene 597, and the obtained longitudinal mode spacing of 1.090 nm almost matched the theoretical spacing. For the first time, we achieved ink-jet printing and lasing of the microdisk cavity by FZ-001, a fluorine-based polymer.

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