Emission gain narrowing has been observed for single crystals of a thiophene/phenylene co-oligomer. The hexagon flake crystals were placed on a quartz substrate with the crystals' face in close contact with the substrate plane. These crystals were irradiated with a N 2 laser with a 337.1 nm wavelength at a repetition rate 10 Hz that tuned its intensity to 100-1150 J/cm 2 . The emission gain narrowing takes place at 21490 ͑465.4 nm͒ and 20220 cm Ϫ1 ͑494.5 nm͒ with increased intensities, with their half width at half maxima reaching ϳ50 cm Ϫ1 . On the basis of the nonlinear relationship between the emission peak intensities and the laser light intensity, the gain narrowing has been attributed to the amplified spontaneous emission. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1435797͔ Conjugated semiconducting polymers and oligomers are currently attracting great attention as potentially useful materials for optoelectronic devices such as thin-film transistors and light-emitting diodes. 1 Solid-state lasing and amplified spontaneous emission ͑ASE͒ have been observed in these materials. 2 Since excitation through photopumping is a facile way to attain lasing and ASE, this method has long been used. [3][4][5] The earliest examples can be found for anthracene molecules embedded in host matrices of, e.g., fluorene. 6 Later this approach was more widely applied to dye-doped systems and polymer thin films. 7 Very recently solid-state injection lasing was achieved using a tetracene single crystal, vouching for the high practicality of organic semiconductors. 8 In view of current injection, crystals of high quality are more advantageous than any other systems that involve defects which may well act as carrier traps. Reported observation of lasing or ASE of the crystals, however, remains scarce even in the case of photopumping. This is partly because the photoluminescent efficiency of chromophores is decreased by higher concentrations, 9 even though their efficiency is high at dilution. Yet a typical examples for the ASE haves been verified by Fichou et al. 10 and by Horowitz et al. 11 using single crystals of octithiophene and sexithiophene, respectively.Yanagi and Morikawa 12 showed that self-waveguided emission takes place along the crystals' long axis of needleshaped crystals of p-sexiphenyl that are epitaxially grown on top of a single crystal substrate of potassium chloride. The molecular axes of p-sexiphenyl align perpendicular to the crystals' needle axis so that the propagation of the polarized emission can be enhanced with the transverse electric mode along that needle. The uniaxially aligned transition dipoles in the p-sexiphenyl crystals are responsible for the selfwaveguided emission. Recent progress demonstrated that this is analogous to the case of a newly emerging class of semiconducting molecular crystals, thiophene/phenylene co-oligomers. 13 These materials were developed by Hotta and co-workers 14 and are characterized by a variety of extensions of conjugation along the backbone. The conjugation ...

Recrystallization from the melt, performed directly on‐substrate, allows the exploitation of the amplified spontaneous emission (ASE) properties of oligo‐phenylene/‐thienylene organic semiconductors in a superior manner (see Figure for a micrograph of the thiophene BP1T on quartz). Upon laser irradiation, a gain‐narrowing of one or more emission lines is observed, partially due to molecular alignment in the recrystallized phase.

We report an organic solid-state distributed feedback laser consisting of an organic active layer and a Bragg grating without morphological change. The active layer consists of 4-͑dicyanomethylene͒-2-methyl-6-͑4-dimethylaminostryl͒-4H-pyran as a laser dye, tris͑8-hydroxyquinoline͒ aluminum as a host, and poly͑methyl methacrylate͒ as a binder. The threshold and linewidth of the laser are 400 J/cm 2 and 1.5 nm, respectively. With this laser, the Bragg grating exists out of the active layer and the grating surface is flat, which are very important for device fabrication and electric driving of the laser. © 2000 American Institute of Physics. ͓S0003-6951͑00͒03243-5͔Recent advances in the materials and structures of organic light-emitting diodes ͑OLEDs͒ ͑Refs. 1-6͒ have opened the door to a generation of light-emitting organic devices, namely, organic semiconductor lasers ͑OSLs͒. Optically pumped solid-state organic lasers are being investigated by many researchers for the realization of OSLs. [7][8][9][10][11][12] Many types of laser structures suitable for organic lasers, for example, microdisks and spheres, vertical-cavity surfaceemitting lasers, distributed Bragg reflectors ͑DBRs͒, and distributed feedback ͑DFB͒ have been demonstrated. The ultimate goal is to develop a ''current-driven'' OSL. Therefore, studies on light-pumped organic lasers should consider the aptitude for electric driving.The efficiency and luminosity of OLED devices have been improved in recent years, making them suitable as the emission mechanism of OSLs. When a resonator is implanted in the OLED, there are many constraints on the resonator. For example, because the OLED consists of thin laminated deposition layers ͑each about 50-80 nm thick͒, steps are not allowed on the substrate and the layers must be flat. In addition, the resonator should be separated from the lightemission part to facilitate fabrication.The DFB resonator is characterized by high efficiency, wavelength selectivity, and ease of fabrication. 13 The surface, however, is not flat. In this letter, we report an organic solid-state laser consisting of an organic active layer and a DFB resonator without morphological modification.A Bragg grating in a planar slab waveguide acting as a DFB resonator was fabricated using the planar lightwave circuit ͑PLC͒ method 14 as follows. First, the core layer was deposited by rf sputtering on a silica substrate. In this layer, germanium was doped to increase the refractive index. The relative refractive index between the core layer and the silica substrate is 0.8%. The thickness of the core layer is 6 m. The Bragg grating is a periodic change in the refractive index of the germanium-doped silica core, fabricated by UV irradiation. Before writing the Bragg grating, the planar slab waveguide was treated with hydrogen loading under high atmospheric pressure to enhance the photosensitivity of the core. The Bragg grating was fabricated in the core layer by irradiating a KrF excimer laser beam emitting light at 248 nm through a phase mask. The pitc...

We demonstrate that fluorescent styrylbenzene derivatives (SBDs) as a guest molecule (10 mol%) in an organic thin-film optical waveguide show excellent gain-narrowing performance by optical pumping. In particular, an extremely low threshold for gain narrowing is obtained with 4,4′-bis[4-(di-p-tolyl-amino)styryl]biphenyl (LD3). In addition, the incorporation of heterocyclic moieties into the styrylbenzene skeletons results in a higher threshold and also causes no spectral narrowing.

Organic microdots were self-organized by vapor deposition of emissive distyrylbenzene derivative molecules onto a cleaved surface of a KCl single crystal. When the deposition amounts were changed at an elevated substrate temperature, the microdot diameters were controlled from the submicrometer scale up to larger than 10 µm. Under optical pumping using a pulse laser, the microdots encapsulated in an MgF 2 layer exhibited amplified spontaneous emission depending on the microdot size. While the spontaneous fluorescence band of the microdots smaller than the cutoff diameter of around 8 µm never collapsed even at high excitation energy, those beyond this size exhibited a gain-narrowed emission peak above a certain threshold energy.