Low Amplified Spontaneous Emission Threshold from Organic Dyes Based on Bis‐stilbene

While noteworthy progress has been made on organic solid‐state lasers with low amplified spontaneous emission (ASE) thresholds and high optical gains in blue and green colors, the same advancement has not been achieved for red laser dyes. This is mainly due to their low photoluminescence quantum yields (PLQYs) because of “energy bandgap law.” Here, a new family of solution‐processable organic semiconductor laser dyes based on a bay‐annulated indigo derivative (Cibalackrot) with deep‐red emission is reported. They exhibit excellent PLQYs and low ASE thresholds (9.6 µJ cm−2) with deep‐red emission when blended in a mixed host of 1,3‐bis(N‐carbazolyl)benzene (mCP) and 2‐hydroxyphenylbenzothiazole (HBT). In contrast to a single blend in mCP, the co‐blend films are found to significantly enhance the photostability by retaining 90% of initial ASE intensity even after continuous pumping with over 9000 pulses at a pump input energy twice that of the ASE threshold, which can be attributed to efficient cascade energy transfer from mCP to HBT and then to the Cibalackrot chromophore. Low lasing threshold of 6 µJ cm−2 is further achieved at 641 nm by using distributed feedback gratings. Transient absorption spectroscopy measurements indicate that the dye has extremely low yield of triplet excited‐state under optical excitation. The results show Cibalackrot derivatives to be a promising new family of organic deep‐red laser dyes.

Section: Resultssupporting

confidence: 86%

Deep‐Red Lasing and Amplified Spontaneous Emission from Nature Inspired Bay‐Annulated Indigo Derivatives

Shukla

Wallwork

et al. 2019

“…Nevertheless, ASE threshold recorded for doped bifluorene crystals is among the lowest reported for organic crystalline materials. [12,14] Although ASE threshold in doped crystals are still below best performing amorphous blend films, [66,67] population inversion can be achieved at significantly lower doping concentrations owing to enhanced energy transfer in well-ordered crystalline materials.…”

Section: Amplified Spontaneous Emissionmentioning

confidence: 99%

Enhanced Energy Transfer in Doped Bifluorene Single Crystals: Prospects for Organic Lasers

Baronas

Kreiza

Mamada

et al. 2019

Self Cite

Organic single crystals with long‐range molecular order ensure enhanced carrier mobility and stability as well as emission outcoupling, which makes them attractive as gain medium for electrically pumped organic lasers. Unfortunately, effects of excitonic coupling introduce losses degrading optical performance in crystals, hence higher lasing thresholds are observed compared to amorphous films. Here, crystal doping strategy is investigated as a method to avoid pronounced reabsorption and annihilation losses associated with J‐type excitonic coupling, while taking advantage of enhanced exciton transport for efficient energy transfer. Bifluorene‐based derivatives linked with acetylene and ethylene rigid bridges are suitable as host and dopant system forming high‐quality crystals doped at various concentrations (0.5–11.0%). Enhanced exciton transport in host crystal mediates picosecond host–dopant energy transfer enabling 100% transfer efficiency at lower doping concentrations compared to amorphous films. Amplified spontaneous emission threshold of 1.9 µJ cm−2 in 3.5% doped crystal is enabled by minimized exciton annihilation and emission reabsorption losses at optimal doping concentration.

“…Among them, 4,4′‐bis[(N‐carbazole)styryl] biphenyl (BSB‐Cz) based on the structure of bis‐stilbene has excellent photophysical properties, including high photoluminescence quantum yield (PLQY) in solid state, high radiative rate constant (kr, 10 9 S −1 ), and very low excited‐state absorption and thus considered to be a very promising candidate for high‐efficiency deep‐blue OLEDs. BSB‐Cz possesses a high PLQY even in neat films, which is contrary to the strong concentration quenching exhibited by many organic dyes . This characteristic property is advantageous to adjust the natural spontaneous emission by utilizing optical microcavity.…”

Section: Introductionmentioning

confidence: 99%

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

Lin

Liu

2020

Despite their rapid development, organic light‐emitting diodes (OLEDs) are limited to display and lighting applications, and exploiting the application and development of OLEDs has become one of the critical issues. In this study, a new type of distributed Bragg reflector (DBR) with low absorption spacer as a bottom mirror is developed through nonquarterwave structural design. Different factors affecting the electroluminescence (EL) properties of microcavity OLEDs (MOLEDs) are investigated by using the optical microcavities with different structures to regulate the EL properties of 4,4′‐bis[(N‐carbazole)styryl] biphenyl (BSB‐Cz). The optimized MOLEDs with quarterwave DBRs exhibited a maximum external quantum efficiency of 8.86 ± 0.06%, demonstrating an enhancement of 79% compared to a reference device. Under the premise of almost not changing the electrical injection of the functional layer materials in the cavity, the spectral full‐width at half maximum of MOLEDs with a nonquarterwave structural design is as narrow as 2 ± 0.05 nm. These improvements are not only suitable for small organic molecules or polymeric materials, but also for novel nanoluminescent materials, such as quantum dots, perovskites, etc. Overall, the current study suggests the general applicability of this novel concept to obtain high‐quality monochromatic light, irrespective of the type of materials used.