Organic Lasers Research Articles

Autonomous Chemical Experiments: Challenges and Perspectives on Establishing a Self-Driving Lab.

We must accelerate the pace at which we make technological advancements to address climate change and disease risks worldwide. This swifter pace of discovery requires faster research and development cycles enabled by better integration between hypothesis generation, design, experimentation, and data analysis. Typical research cycles take months to years. However, data-driven automated laboratories, or self-driving laboratories, can significantly accelerate molecular and materials discovery. Recently, substantial advancements have been made in the areas of machine learning and optimization algorithms that have allowed researchers to extract valuable knowledge from multidimensional data sets. Machine learning models can be trained on large data sets from the literature or databases, but their performance can often be hampered by a lack of negative results or metadata. In contrast, data generated by self-driving laboratories can be information-rich, containing precise details of the experimental conditions and metadata. Consequently, much larger amounts of high-quality data are gathered in self-driving laboratories. When placed in open repositories, this data can be used by the research community to reproduce experiments, for more in-depth analysis, or as the basis for further investigation. Accordingly, high-quality open data sets will increase the accessibility and reproducibility of science, which is sorely needed.In this Account, we describe our efforts to build a self-driving lab for the development of a new class of materials: organic semiconductor lasers (OSLs). Since they have only recently been demonstrated, little is known about the molecular and material design rules for thin-film, electrically-pumped OSL devices as compared to other technologies such as organic light-emitting diodes or organic photovoltaics. To realize high-performing OSL materials, we are developing a flexible system for automated synthesis via iterative Suzuki-Miyaura cross-coupling reactions. This automated synthesis platform is directly coupled to the analysis and purification capabilities. Subsequently, the molecules of interest can be transferred to an optical characterization setup. We are currently limited to optical measurements of the OSL molecules in solution. However, material properties are ultimately most important in the solid state (e.g., as a thin-film device). To that end and for a different scientific goal, we are developing a self-driving lab for inorganic thin-film materials focused on the oxygen evolution reaction.While the future of self-driving laboratories is very promising, numerous challenges still need to be overcome. These challenges can be split into cognition and motor function. Generally, the cognitive challenges are related to optimization with constraints or unexpected outcomes for which general algorithmic solutions have yet to be developed. A more practical challenge that could be resolved in the near future is that of software control and integration because few instrument manufacturers design their products with self-driving laboratories in mind. Challenges in motor function are largely related to handling heterogeneous systems, such as dispensing solids or performing extractions. As a result, it is critical to understand that adapting experimental procedures that were designed for human experimenters is not as simple as transferring those same actions to an automated system, and there may be more efficient ways to achieve the same goal in an automated fashion. Accordingly, for self-driving laboratories, we need to carefully rethink the translation of manual experimental protocols.

Random lasing of the active organic nanocrystals of SFX-2-7-DDPA solution

In this paper, we demonstrated organic nanocrystals micro-lasers devices with different thickness from 0.4mm to 0.7mm. The N2, N2, N7, N7-tetraphenylspiro [fluorene-9,9-xanthene]-2,7-diamine, 95% (SFX-2-7-DDPA) structure (organic nanocrystals in a solution)- highly scattering medium is manipulated to generate a multiple light scattering. The manufacture technique can be used to a variety of water soluble SFX-2-7-DDPA, designed to work in the gain ethanol solution with SFX-2-7-DDPA nanocrystals devices, has been investigated at different input powers. A Nd-YAG laser based experiment tool has been measured including a from amplified spontaneous emission to random lasing. The analysis of photon travel distance has been thought about showing the random lasing behavior with particular attention on lasing tunability by using devices of different sizes. Particulary,for first time, we have demonstrated dye-doped SFX-2-7-DDPA nanocrystals based organic random lasers.

Effect of structural modifications on the spectral and lasing characteristics of truxene-cored starbursts with/without diphenylamine end-cappers

This study examined the effect of chemical modifications on the spectral and lasing characteristics of truxene-cored starbursts as gain media for organic lasers. A series of conjugated starburst materials, consisting of a truxene core and oligofluorene bridges with and without diphenylamine (DPA), namely, TrXD and TrX, were assessed as model molecules to investigate the influence of DPA on the photophysical characteristics and organic lasing behaviors. TrXD with DPA could effectively restrain the aggregation and greatly suppress the aggregation-induced emission quenching, yielding high photoluminescence efficiency. A higher radiative decay rate kr was observed for TrXD than for TrX, suggesting that DPA is beneficial for enhancing the radiative decay process. TrXD showed low amplified spontaneous emission thresholds of 2.1–4.3 μJ cm−2 with high net gain coefficients of 80–101 cm−1, rather low loss coefficients of 2.6–4.4 cm−1, compared with TrX. The best performance with a lasing threshold of 0.31 kW cm−2 was obtained for Tr3D, which was superior to that of Tr3 (0.86 kW cm−2). The molecular systems with DPA have a large potential as attractive molecules for organic lasers because of the superior lasing properties induced by kr.

High-Performance Organic Laser Semiconductor Enabling Efficient Light-Emitting Transistors and Low-Threshold Microcavity Lasers.

An organic light-emitting transistor (OLET) is a candidate device architecture for developing electrically pumped organic solid-state lasers, but it remains a critical challenge because of the lack of organic semiconductors that simultaneously possess a high solid-state emission efficiency (Φs), a high and balanced ambipolar mobility (μh,e), and a large stimulated emission cross-section. Here, we designed a molecule of 4,4'-bis(2-dibenzothiophenyl-vinyl)-biphenyl (DBTVB) and prepared its ultrathin single-crystal microplates with herringbone packing arrangements, which achieve balanced mobilities of μh = 3.55 ± 0.5 and μe = 2.37 ± 0.5 cm2 V-1 s-1, a high Φs of 85 ± 3%, and striking low-threshold laser characteristics. Theoretical and experimental investigations reveal that a strong electronic coupling and a small reorganization energy ensure efficient charge transport; meanwhile, the exciton-vibration effect and negligible π-π orbital overlap give rise to highly emissive H-aggregates and facilitate laser emission. Furthermore, OLET-based DBTVB crystals offer an internal quantum efficiency approaching 100% and a record-high electroluminescence external quantum efficiency of 4.03%.

Asymmetric AZA-BODIPY with Optical Gain in the Near-Infrared Region.

In recent years, there has been a lot of interest in the development of organic compounds emitting in the near-infrared (NIR) region due to their stimulating applications, such as biosensing and light detection and ranging (LiDAR). Moreover, a lot of effort has been devoted to finding organic emitters with optical gain in the NIR region for lasing applications. In this paper, we present the ultrafast spectroscopy of an asymmetric AZA-BODIPY molecule that shows relevant photophysical changes moving from a diluted solution to a concentrated solution and to a spin-coated film. The diluted solution and the spin-coated film show a bleaching band and a stimulated emission band in the visible region, while the very concentrated solution displays a broad (150 nm) and long-living (more than 400 ps) optical gain band in the NIR region, centered at 900 nm. Our results pave the way for a new organic laser system in a near-infrared spectral region.

Impact of excitonic and photonic loss mechanisms on the threshold and slope efficiency of organic semiconductor lasers

We investigated the impact of various excitonic and photonic losses on the lasing threshold and slope efficiency of organic semiconductor lasers (OSLs) under optical and electrical excitations. The rate equations are solved numerically using the Euler method for an OSL and an organic semiconductor laser diode, including 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) as a gain medium. The results showed that the loss mechanisms that affect the exciton and photon densities cause an increase in the laser threshold and a decrease in the slope efficiency. Further, we demonstrated that by using a thermally activated delayed fluorescence (TADF) emitter as a gain medium, the triplet excitons could be harvested by increasing the reverse intersystem crossing rate (k RISC ), resulting in an appreciable decrease of the laser threshold and an increase of the slope efficiency. Accordingly, the TADF emitters with a fast k RISC are expected to significantly reduce the current density required for electrical excitation.

Enhanced lasing properties of BUBD-1 film with multifunctional buffer layers doped with silver nanoparticles.

The organic semiconductor lasers (OSLs) have been seen as a promising light source for future applications. Achieving organic semiconductors with low amplified spontaneous emission (ASE) threshold is a key progress toward the electrically pumped OSLs. In this paper, the ASE properties of CBP: 2wt% BUBD-1 blend films were optimized using buffer layers containing silver nanoparticles (Ag NPs) with different ratios. Both photoluminescence intensity and ASE properties of blend films were optimized when the buffer layer with 25 vol% Ag NPs was introduced. The lowest ASE threshold is 0.47 µJ/Pulse (6.71 µJ/cm2), which reduces 67.6%, and the highest gain factor is 20.14 cm-1, which enhances 47.8% compared with that without buffer layers. The enhancement of ASE properties of blend films was ascribed to the four functions of the Ag NPs doped buffer layers, including the low refractive index of PMMA and the triple localized surface plasmon resonance (LSPR) effects of Ag NPs in buffer layers. The results show that the buffer layer modified by metal nanoparticles has great application potential in improving the lasing performance of organic small molecules.

Amplified Spontaneous Emission from Organic Phosphorescence Emitters.

Organic gain materials (OGMs) currently used in organic lasers and optical amplifiers are focused on singlet-fluorescence materials, while triplet-phosphorescence-based OGMs have hardly been developed yet. Herein, we report a novel pure organic phosphorescence gain molecule (SBP) for optical amplification by stimulated emission from triplet states. The introduction of the benzophenone carbonyl group and sulfur atoms increases the spin orbit coupling constant of SBP, which accelerates the intersystem crossing (ISC) and phosphorescence processes. Experimental and theoretical results verify that the formation of the H-type dimer aggregate decreases the fluorescence radiation rate while accelerating the ISC rate, also enhancing the phosphorescence emission of SBP. Doping SBP molecules into a PMMA matrix can stabilize triplet excitons, yielding the maximum phosphorescence quantum yield of 18.9%. We realized triplet phosphorescent amplified spontaneous emission (ASE) at 557 nm from 30.0 wt % SBP@PMMA samples. Our results provide a novel strategy to develop triplet phosphor OGMs.

Organic molecular crystal with a high ultra-deep-blue emission efficiency of ∼85% for low-threshold laser

Organic crystal with a high emission efficiency and excellent spectral stability is crucial for constructing low-threshold deep-blue organic laser. Here, we synthesized an organic lasing molecule (BPhDPF) with a steric diarylfluorene as the core building block, the single crystal of which has ultra-deep-blue emission with the photoluminescence quantum yield (PLQY) as high as 84.9%, as well as short lifetime and super-stable emission. Meanwhile, C-H ⋯ π interactions are easily observed in single crystal structure, contributing to the formation of BPhDPF polyhedral microcrystals by self-organize in solution. Interestingly, the intermolecular coupling and exited state were well inhibited by the large steric hindrance group at 9-position and 2-/7- flexible side-chain, which is critical to laser applications. Finally, the deep-blue emission organic laser was obtained with a peak located at 418 nm and very low threshold of Pth = 1.62 μJ cm−2. A novel organic lasing molecule has been developed, offering helpful information for further investigating organic lasers.

Optical Properties of Malachite Green Organic Laser Dye Doped with PMMA Polymer and Cu Nanoparticles

In this work, optical properties for a Malachite Green organic laser dye doped PMMA polymer and Cu nanoparticles were studied at concentrations (2×10-5,4×10-5,6×10-5 and 8×10-5) M in chloroform solvent. Absorption and transmission spectra of all samples has been recorded using UV-VIS spectrometer. When compared the samples of pure organic dye and dye doped PMMA polymer and with Cu nanoparticles, the results show that organic dye doped Cu nanoparticles have very high linear optical characteristics. This result showed that these organic dye doped with nanoparticles are very suitable for applications in optical and photonic devices.

Controlling triplet\u2013triplet upconversion and singlet-triplet annihilation in organic light-emitting diodes for injection lasing

Significant progress has recently been made in the field of organic solid-state lasers. However, achieving lasing action from organic semiconductors under electrical excitation remains challenging due to losses introduced by triplet excitons. Here, we report experimental and theoretical results that confirm a positive contribution of triplet excitons for electrically-driven organic lasing via a bimolecular triplet-triplet upconversion (TTU) mechanism. We study a model fluorescent material, 9-(9-phenylcarbazole-3-yl)-10-(naphthalene-1-yl)anthracene, revealing that TTU can lower the threshold current densities required to achieve lasing under current injection. However, to achieve the best performance, the singlet-triplet annihilation (STA) must be simultaneously minimized. Hence, an experimental strategy to simultaneously obtain high TTU with low STA is demonstrated in host-guest system with coumarin 545T as the guest laser dye. This system has a low amplified spontaneous emission threshold of 1.7 µJ cm−2 under nanosecond optical pumping, and a more than three orders of magnitude improvement in J50 in organic light-emitting diodes as compared to a reference blend.

Integrating Unexpected High Charge-Carrier Mobility and Low-Threshold Lasing Action in an Organic Semiconductor.

Integrating high charge-carrier mobility and low-threshold lasing action in an organic semiconductor is crucial for the realization of an electrically pumped laser, but remains a great challenge. Herein, we present an organic semiconductor, named as 2,7-di(2-naphthyl)-9H-fluorene (LD-2), which shows an unexpected high charge-carrier mobility of 2.7 cm2 V-1 s-1 and low-threshold lasing characteristic of 9.43 μJ cm-2 and 9.93 μJ cm-2 and high-quality factor (Q) of 2131 and 1684 at emission peaks of 420 and 443 nm, respectively. Detailed theoretical calculations and photophysical data analysis demonstrate that a large intermolecular transfer integral of 10.36-45.16 meV together with a fast radiative transition rate of 8.0×108 s-1 are responsible for the achievement of the superior integrated optoelectronic properties in the LD-2 crystal. These optoelectronic performances of LD-2 are among the highest reported low-threshold lasing organic semiconductors with efficient charge transport, suggesting its promise for research of electrically pumped organic lasers (EPOLs).

Integrating Unexpected High Charge‐Carrier Mobility and Low‐Threshold Lasing Action in an Organic Semiconductor

AbstractIntegrating high charge‐carrier mobility and low‐threshold lasing action in an organic semiconductor is crucial for the realization of an electrically pumped laser, but remains a great challenge. Herein, we present an organic semiconductor, named as 2,7‐di(2‐naphthyl)‐9H‐fluorene (LD‐2), which shows an unexpected high charge‐carrier mobility of 2.7 cm2 V−1 s−1 and low‐threshold lasing characteristic of 9.43 μJ cm−2 and 9.93 μJ cm−2 and high‐quality factor (Q) of 2131 and 1684 at emission peaks of 420 and 443 nm, respectively. Detailed theoretical calculations and photophysical data analysis demonstrate that a large intermolecular transfer integral of 10.36–45.16 meV together with a fast radiative transition rate of 8.0×108 s−1 are responsible for the achievement of the superior integrated optoelectronic properties in the LD‐2 crystal. These optoelectronic performances of LD‐2 are among the highest reported low‐threshold lasing organic semiconductors with efficient charge transport, suggesting its promise for research of electrically pumped organic lasers (EPOLs).

Octagonal Quasicrystal Defect Mode Laser-Based PVK: Ir(ppy)3 Polymer Driven by Optical Pumping.

Based on the conjugated complex PVK: Ir(ppy)3, a green-emitting organic quasicrystal microcavity laser is demonstrated driven by optical pumping. The organic laser adopts a sandwich structure of DBR/organic gain membrane/output Ag-layer for the vertical oscillation and an octagonal quasi-crystal for in-plane light localization. The experimental results show that the single-mode lasing action is observed at 521 nm with an FWHM of 0.8 nm. The threshold of lasing is lowered to 0.181 μJ/cm2.

Low Light Amplification Threshold and Reduced Efficiency Roll-Off in Thick Emissive Layer OLEDs from a Diketopyrrolopyrrole Derivative.

External quantum efficiency (EQE) roll-off under high current injection has been one of the major limiting factors toward the development of organic semiconductor laser diodes (OSLDs). While significant progress in this regard has been made on organic semiconductors (OSCs) emitting in the blue-green region of the visible spectrum, OSCs with longer wavelength emission (>600nm) have fallen behind in both material development and the advancement in device architectures suitable for the realization of OSLDs. Therefore, to make simultaneous incremental advancements, a host-guest system comprising of a high performing poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) polymer and an efficient small molecule laser dye, dithiophenyl diketopyrrolopyrrole (DT-DPP), is used. This combination provides an extremely low amplified spontaneous emission threshold of 4.2µJcm-2 at an emission wavelength of 620nm. The solution-processed organic light-emitting diodes (OLEDs) fabricated using this system exhibit a high external quantum efficiency (EQE) of 2.6% with low efficiency roll-off and high current injection up to 90Acm-2 to yield ultrahigh luminance of over 1.5millioncdm-2 .

Optically pumped lasing in a single crystal cavity of thiophene/phenylene co-oligomers grown via improved crystal growth methods in solution

Single crystals of thiophene/phenylene co-oligomers (TPCOs) are promising organic laser media. Owing to their poor solubility in solvents, single crystals of TPCOs have conventionally been grown using sublimation processes. However, the morphology of the grown crystals is not ideal for lasing by the self-cavity effect. In this report, single crystals of 5,5‴-bis(4-biphenylyl)-2,2′:5′,2″:5″,2‴-quaterthiophene (BP4T), which is one of the longest TPCOs, are grown through improved methods in solution to achieve lasing with a well-shaped single crystal cavity. The high quality factors (5.9 × 103) and group refractive indexes (>3.5) suggest that the obtained crystals are superior organic laser media.

Linear Optical Properties of Organic Laser Dye Doped with PMMA Polymer

In this work, linear optical characteristics of Azure B organic laser dye doped with PMMA polymer dissolved in DMF solvent at concentration (1×10-3 M) were studied. This research includes presenting the results and discussing the absorption spectra and linear optical properties (transmission, linear absorption and refraction coefficient), by studying the effect of adding polymer (PMMA) with different ratios on this pure dye. The result showed that possibility of using this dye in liquid state laser.

Highly photo-stable, kHz-repetition-rate, diode pumped circulation-free liquid dye laser with thermal lens management

Liquid dye lasers have long been considered as ideal tunable laser sources in the visible range but are bulky, expensive, and require a complex system for dye circulation. Here, we present a system that relies on a low-cost blue laser diode as the pump source and a sealed dye cell with no flowing circuitry, resulting in a device that combines the convenience and size of a solid-state device with the stability of a liquid organic laser. A very high photo-stability is obtained (up to 1.2 × 109 pulses or 12 days at 1 kHz), which is five orders of magnitude higher than a solid-state dye laser operated in similar conditions. The number of pulses obtainable at low repetition rates is found to be limited by molecular self-diffusion and, hence, related to the total cuvette volume. In contrast, the repetition rate is limited to a few kHz, which suggests that thermal effects play a bigger role than triplet population effects. Thermal effects participate in the suppression of lasing through the buildup of a strong negative thermal lens; correcting the non-aberrant part of this thermal lens by resonator design enables the repetition rate to be pushed up to 14 kHz with possible further optimization. This work shows a route for building off-the-shelf, compact, low-cost, and convenient tunable pulsed lasers in the visible range that have superior stability over organic solid-state lasers.

Single‐, Dual‐, Triple, and Quadruple‐Wavelength Surface‐Emitting Lasing in Blue‐Phase Liquid Crystal (Adv. Mater. 9/2022)

Organic Lasers Single-, dual-, triple- to quad-wavelength lasers can be flexibly manipulated based on polymer-stabilized blue-phase liquid-crystal film, by tuning the bandgap, resonance cavity, order parameter of the laser dye, and even the pump energy. The single-to-quad-wavelength surface-emitting lasers proposed by Feng Jin, Jingxia Wang, and co-workers in article number 2108330, can be employed as coherent light sources for next-generation optical devices.

Effect of dye on luminescent and nonlinear optical properties of bis(4-methoxybenzylammonium) tetra-chlorido cadmate (4MBA2CdCl4) perovskite

We report luminescence and optical limiting (OL) applications of pure and doped layered hybrid halide perovskite (LHHP). Rhodamine B (Rh B), an organic laser dye, was doped in bis(4-methoxybenzylammonium) tetra-chlorido cadmate (4MBA2CdCl4). A simple and cost-effective slow solvent evaporation technique was utilized for crystallization of the perovskites. Formation of both pure and doped 4MBA2CdCl4 were confirmed from the X-ray diffraction (XRD) and Fourier transform infrared (FTIR) studies. 4MBA2CdCl4 crystallized as a layered perovskite where organic layers (4MBA+) are sandwiched between the distorted inorganic CdCl4− octahedral layers. The perovskites are thermally stable up to 276 °C and are flexible up to a load of 50 g. Optical absorption of pure perovskite falls in UV region and is highly transparent for visible light. But, inclusion of Rh B reflected a new absorption peak in the visible region. Also, the luminescence under UV excitation of 4MBA2CdCl4 modified due to doping of dye and it exhibit strong golden yellow luminescence. Nonlinear optical (NLO) properties of pure and doped 4MBA2CdCl4 were also studied by Z-scan technique using 785 nm continuous wave (CW) laser. The perovskites exhibited reverse saturable absorption (RSA) and self-defocusing. Further, both perovskites demonstrate optical limiting properties with a low intensity threshold of 0.8 MW/m2. Rh B incorporated 4MBA2CdCl4 exhibit interesting and enhanced photoluminescence and OL behaviours.