Concurrent Optical Gain Optimization and Electrical Tuning in Novel Oligomer:Polymer Blends with Yellow-Green Laser Emission

Dual-Color Lasers in Interlayer-Free Solution Processed Polymeric Bilayer Devices

Multiwavelength organic lasers have attracted considerable interest in recent years due to the cost efficiency, wide luminescence coverage, and simple processability of organics. In this work, by simply spin coating immiscible polymeric gain media in sequence, dual-wavelength (blue-green or blue-red) amplified spontaneous emission (ASE) was achieved in bilayer devices. The blue emission, water/alcohol-soluble conjugated polyelectrolyte, poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide (PFN-Br), was used as the bottom layer. The commercially available nonpolar solvent soluble polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and its blend with poly(3-hexylthiophene) (P3HT) were used as the top active layers offering green and red emission, respectively. This novel compact configuration, without interlayers between the two active layers, offers potential for developing various applications. The carefully selected top and bottom layer polymers not only meet the conditions of immiscibility and different emission wavelength range but also have a common absorption band in UV, which allows simultaneous blue-green or blue-red dual-color ASE behaviors observed in the bilayer devices under the same 390 nm laser excitation. By introducing two-dimension (2D) square distributed feedback (DFB) gratings with different periods (300 nm for blue, 330 nm for green, and 390 nm for red) as cavities, single mode blue-green (Eth = 245 μJ cm-2) and blue-red (Eth = 189 μJ cm-2) lasers were achieved by focusing the excitation laser spot on different 2D DFB gratings area. Furthermore, we found it possible to gain sufficient light confinement for red emission along its diagonal direction (Λ ∼424 nm), whereas the 2D DFB gratings offer feedback for blue emission from the 300 nm period along the rectangle direction. Therefore, both blue and red lasers were eventually achieved in the same PFN-Br/F8BT:P3HT bilayer device on the single 2D DFB gratings with a period of 300 nm in this work.

Process intensified synthesis of luminescent poly(9,9-dioctylfluorene-alt-benzothiadiazole) and polyvinyl alcohol based shape memory polymeric nanocomposite sensors toward cold chain logistics information monitoring

Luminescent shape memory polymeric nanocomposite sensors prepared using poly(9,9-dioctylfluorene-alt-benzothiadiazole) and polyvinyl alcohol for cold chain logistics information monitoring.

Organic Semiconductor Micro/Nanocrystals for Laser Applications

Organic semiconductor micro/nanocrystals (OSMCs) have attracted great attention due to their numerous advantages such us free grain boundaries, minimal defects and traps, molecular diversity, low cost, flexibility and solution processability. Due to all these characteristics, they are strong candidates for the next generation of electronic and optoelectronic devices. In this review, we present a comprehensive overview of these OSMCs, discussing molecular packing, the methods to control crystallization and their applications to the area of organic solid-state lasers. Special emphasis is given to OSMC lasers which self-assemble into geometrically defined optical resonators owing to their attractive prospects for tuning/control of light emission properties through geometrical resonator design. The most recent developments together with novel strategies for light emission tuning and effective light extraction are presented.

F8BT Oligomers for Organic Solid-State Lasers

The yellow-green emissive poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) polymer is widely used because of its suitability for a variety of applications. However, we have found that F8BT shows huge performance variations that depend on the chemical supplier, with photoluminescence quantum yields (PLQYs) ranging from 7 to 60% in neat films. Polymers generally face problems including purity, polydispersity, and reproducibility, which also affect F8BT polymers. Therefore, to overcome these problems, we investigated oligomers of F8BT, which can easily be purified and can thus be obtained in a high-purity form. In the three oligomers (M1-M3) that we synthesized, the PLQYs were much higher than those of conventional F8BT (>80% in their neat films) although their PL spectra were nearly the same as that of F8BT, and their amplified spontaneous emission (ASE) thresholds were lower than that of the polymer (e.g., 1.9 μJ cm^-2 for M3 and 2.7 μJ cm^-2 for F8BT) because of a higher net gain and better film morphology. Furthermore, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies of the oligomers were found to be similar to those of F8BT, making them candidate materials for use as hosts in light-emitting devices. The ASE using a near-infrared laser emitter doped in F8BT and oligomer hosts showed a clear difference despite nearly the same properties for steady-state emission.