Low‐Threshold Distributed‐Feedback Lasers Based on Pyrene‐Cored Starburst Molecules with 1,3,6,8‐Attached Oligo(9,9‐Dialkylfluorene) Arms

Here, a detailed characterization of the optical gain properties of sky‐blue‐light‐emitting pyrene‐cored 9,9‐dialkylfluorene starbursts is reported; it is shown that these materials possess encouragingly low laser thresholds and relatively high thermal and environmental stability. The materials exhibit high solid‐state photoluminescence (PL) quantum efficiencies (>90%) and near‐single‐exponential PL decay transients with excited state lifetimes of ～1.4 ns. The thin‐film slab waveguide amplified spontaneous emission (ASE)‐measured net gain reaches 75–78 cm^?1. The ASE threshold energy is found to remain unaffected by heating at temperatures up to 130 °C, 40 to 50 °C above T_g. The ASE remained observable for annealing temperatures up to 170 or 200 °C. 1D distributed feedback lasers with 75% fill factor and 320 nm period show optical pumping thresholds down to 38–65 Wcm^?2, laser slope efficiencies up to 3.9%, and wavelength tuning ranges of ～40 nm around 471–512 nm. In addition, these lasers have relatively long operational lifetimes, with N_1/2 ≥ 1.1 × 10⁵ pulses for unencapsulated devices operated at ten times threshold in air.     

Covalently Tethered Polyoxometalate–Pyrene Hybrids for Noncovalent Sidewall Functionalization of Single‐Walled Carbon Nanotubes as High‐Performance Anode Material

A covalently tethered polyoxometalate (POM)–pyrene hybrid (Py–SiW₁₁) is utilized for the noncovalent functionalization of single‐walled carbon nanotubes (SWNTs). The resulting SWNTs/Py–SiW₁₁ nanocomposite shows that both SiW₁₁ and pyrene moieties could interact with SWNTs without causing any chemical decomposition. When used as anode material in lithium‐ion batteries, the SWNTs/Py–SiW₁₁ nanocomposite exhibits higher discharge capacities, and better rate capacity and cycling stability than the individual components. When the current density is 0.5 mA cm^?2, the nanocomposite exhibits the initial discharge capacity of 1569.8 mAh g^?1, and a high discharge capacity of 580 mAh g^?1 for up to 100 cycles.     

Low-Threshold,External-Cavity-Free Flexible Perovskite Lasers

A distinct advantage of halide perovskite semiconductors is their potential as gain media in high-performance, all-solution-processed flexible lasers. However, most perovskite microlasers employ external optical resonators with rigid and high-temperature/vaccum-processed structures unsuitable for flexible applications. Here, low-threshold, external-cavity-free perovskite lasers (≈550 nm, linewidth: ≈0.3 nm, quality factor: ≈1900, room temperature), prepared with excellent reproducibility using simple one-step spin-coating and low-temperature annealing, are demonstrated. Exceptionally low lasing thresholds of 9.3 and 14.6 µJ cm⁻² are achieved for external-cavity-free perovskite lasers on rigid and flexible substrates, respectively. The thresholds and quality factors are on par with that of high-performance perovskite microlasers with well-designed external cavities. The lasers exhibit good operational stability, showing half-life of >1.8 × 10⁸ pulses under optical pumping in air. Transient optical experiments reveal that the low thresholds stem from enhanced band-to-band spontaneous and stimulated emission processes in the high-quality microcrystalline perovskite, effectively out-pacing trap-mediated and Auger processes detrimental to the lasing action. The flexible perovskite lasers retain >95% of the initial intensity after 10000 bending cycles, showing outstanding mechanical durability. As these lasers can be produced from solution within minutes at low costs, the findings are expected to enable high-throughput, scalable fabrication of perovskite lasers for emerging applications.     

Coreless Fiber‐Based Whispering‐Gallery‐Mode Assisted Lasing from Colloidal Quantum Well Solids

Whispering gallery mode (WGM) resonators are shown to hold great promise to achieve high‐performance lasing using colloidal semiconductor nanocrystals (NCs) in solution phase. However, the low packing density of such colloidal gain media in the solution phase results in increased lasing thresholds and poor lasing stability in these WGM lasers. To address these issues, here optical gain in colloidal quantum wells (CQWs) is proposed and shown in the form of high‐density close‐packed solid films constructed around a coreless fiber incorporating the resulting whispering gallery modes to induce gain and waveguiding modes of the fiber to funnel and collect light. In this work, a practical method is presented to produce the first CQW‐WGM laser using an optical fiber as the WGM cavity platform operating at low thresholds of ≈188 µJ cm^?2 and ≈1.39 mJ cm^?2 under one‐ and two‐photon absorption pumped, respectively, accompanied with a record low waveguide loss coefficient of ≈7 cm^?1 and a high net modal gain coefficient of ≈485 cm^?1. The spectral characteristics of the proposed CQW‐WGM resonator are supported with a numerical model of full electromagnetic solution. This unique CQW‐WGM cavity architecture offers new opportunities to achieve simple high‐performance optical resonators for colloidal lasers.     

Fluorescent,Carrier‐Trapping Dopants for Highly Efficient Single‐Layer Polyfluorene LEDs

Two fluorescent molecules with an alkynylanthracene core and pyrene end‐cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enhance the hole‐transport ability of the molecule and to reduce intermolecular interactions. Both compounds exhibit high thermal stabilities and narrow energy bandgaps. Single‐layer polymer light‐emitting diodes (PLEDs) based on poly(9,9‐dioctylfluorene) (PFO) doped with the synthesized compounds exhibit excellent performance. A PLED with 0.2 % of dopant 7 had a high luminance efficiency of 10.7 ± 0.3 cd A^–1 as well as a brightness of 1400 cd m^–2 at a current density of 13 mA cm^–2, and a low turn on voltage (3.1 V) at a brightness of 10 cd m^–2. A maximum brightness of 20 500 ± 1400 cd m^–2 at 7 V was also measured. The high efficiency of the device's performance is attributed to the good electron and hole trapping ability of the dopants, which possess suitable energy levels as compared to those of PFO.     

Lasing in Cd(Zn)Se/ZnMgSSe heterostructures pumped by nitrogen and InGaN/GaN lasers

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm², a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T ₀=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.     

Ambient‐Stable,Annealing‐Free,and Ambipolar Organic Field‐Effect Transistors Based on Solution‐Processable Poly(2,2′‐bis(trifluoromethyl)biphenyl‐alt‐2,5‐divinylthiophene) without Long Alkyl Side Chains

An ambipolar conjugated polymer CF₃‐PBTV, poly(2,2′‐bis(trifluoromethyl)biphenyl‐alt‐2,5‐divinylthiophene), consisting of thienylenevinylene as the donor and trifluoromethyl‐substituted biphenyl as the acceptor has been successfully synthesized. CF₃‐PBTV shows solution‐processability without electrically insulating long alkyl side chains. Grazing incidence X‐ray diffraction results suggest a nearly equal population of flat‐on and end‐on domains in CF₃‐PBTV thin film. The excellent ambipolarity of CF₃‐PBTV is demonstrated by well‐equivalent charge mobilities of 0.065 and 0.078 cm² V^?1 s^?1 for p‐ and n‐channel, respectively. The organic field‐effect transistors (OFET) also shows very high on/off ratio (≈10⁷) which is attributed to the relatively large bandgap and low‐lying highest occupied molecular orbital (HOMO) of CF₃‐PBTV. The OFET performance barely changes after the device is stored in ambient conditions for 90 days. The ambient‐stability is attributed to the enhanced oxidative stability from its low‐lying HOMO and the better moisture resistance from its fluorine contents. The performance of CF₃‐PBTV based OFET is annealing independent. It is noteworthy that the solution‐processable, ambipolar, and thienylenevinylene‐containing conjugated polymer without any long alkyl side chains is reported for the first time. And to the best of our knowledge, it is the first ambient‐stable, annealing‐free OFET with well‐equivalent ambipolarity.     

Multiphoton‐Pumped Highly Polarized Polariton Microlasers from Single Crystals of a Dye‐Coordinated Metal–Organic Framework

Room‐temperature, low‐threshold, photostable, cost‐effective, efficient, miniaturized, and all‐solid‐state lasers are highly desirable in many technological and medicinal applications. Here, an archetypical dye laser is introduced, with the above attributes, based on single‐crystalline microplates of a dye‐coordinated metal–organic framework (MOF) without an external cavity, holding a potential to be the next‐generation laser. With an exciton–polariton lasing mechanism combined with large multiphoton absorption cross sections, the lasing thresholds of the three microplates are in the range from 0.34 to 0.12 µJ cm^?2 under various optical pumping schemes. The lasing threshold is observed to be reduced with an increment in the order of optical nonlinearity involved in the pumping scheme. Lasing at an extreme‐red region is demonstrated, with a high photostability (with a drop in lasing output as low as 25% after 1.8 × 10⁶ cycles), a large degree of polarization (up to 92%), and an excellent conversion efficiency (up to 12%), thereby realizing a crucial milestone in the field of laser technology.     

Red,Green, and Blue Light‐Emitting Polyfluorenes Containing a Dibenzothiophene‐S,S‐Dioxide Unit and Efficient High‐Color‐Rendering‐Index White‐Light‐Emitting Diodes Made Therefrom

A series of blue (B), green (G) and red (R) light‐emitting, 9,9‐bis(4‐(2‐ethyl‐hexyloxy)phenyl)fluorene (PPF) based polymers containing a dibenzothiophene‐S,S‐dioxide (SO) unit (PPF‐SO polymer), with an additional benzothiadiazole (BT) unit (PPF‐SO‐BT polymer) or a 4,7‐di(4‐hexylthien‐2‐yl)‐benzothiadiazole (DHTBT) unit (PPF‐SO‐DHTBT polymer) are synthesized. These polymers exhibit high fluorescence yields and good thermal stability. Light‐emitting diodes (LEDs) using PPF‐SO25, PPF‐SO15‐BT1, and PPF‐SO15‐DHTBT1 as emission polymers have maximum efficiencies LE_max = 7.0, 17.6 and 6.1 cd A^?1 with CIE coordinates (0.15, 0.17), (0.37, 0.56) and (0.62, 0.36), respectively. 1D distributed feedback lasers using PPF‐SO30 as the gain medium are demonstrated, with a wavelength tuning range 467 to 487 nm and low pump energy thresholds (≥18 nJ). Blending different ratios of B (PPF‐SO), G (PPF‐SO‐BT) and R (PPF‐SO‐DHTBT) polymers allows highly efficient white polymer light‐emitting diodes (WPLEDs) to be realized. The optimized devices have an attractive color temperature close to 4700 K and an excellent color rendering index (CRI) ≥90. They are relatively stable, with the emission color remaining almost unchanged when the current densities increase from 20 to 260 mA cm^?2. The use of these polymers enables WPLEDs with a superior trade‐off between device efficiency, CRI, and color stability.     

Cyano‐Substituted Oligo(p‐phenylene vinylene) Single Crystals: A Promising Laser Material

Organic crystals that combine high charge‐carrier mobility and excellent light‐emission characteristics are expected to be of interest for light‐emitting transistors and diodes, and may offer renewed hope for electrically pumped laser action. High‐luminescence‐efficiency cyano‐substituted oligo(p‐ phenylene vinylene) (CN‐DPDSB) crystals (η ≈ 95%) grown by the physical vapor transport method is reported here, with high mobilities (at ≈10^?2 cm² V^?1 s^?1 order of magnitude) as measured by time‐of‐flight. The CN‐DPDSB crystals have well‐balanced bipolar carrier‐transport characteristics (μ_hole≈ 2.5–5.5 × 10^?2 cm² V^?1 s^?1; μ_electron ≈ 0.9–1.3 × 10^?2 cm² V^?1 s^?1) and excellent optically pumped laser properties. The threshold for amplified spontaneous emission (ASE) is about 4.6 μJ per pulse (23 KW cm^?2), while the gain coefficient at the peak wavelength of ASE and the loss coefficient caused by scattering are ≈35 and ≈1.7 cm^?1, respectively. This indicates that CN‐DPDSB crystals are promising candidates for organic laser diodes.     

MOVPE of ZnMgSSe heterostructures for optically pumped blue-green lasers

We report on the growth of ZnMgSSe/ZnSSe/ZnSe heterostructures in a low pressure metalorganic vapor phase epitaxy (MOVPE) system at 400 hPa and a growth temperature of 330°C. The precursor combination was dimethylzinc(triethylamine adduct), ditertiarybutylselenium, ditertiarybutylsulphur, and bismethylcyclopentadienylmagnesium. This combination allows the reproducible adjustment of the alloy composition in a wide range (currently up to 40% S and 32% Mg) maintaining high crystal homogeneity and almost lattice matched growth. Undoped separate confinement heterostructure (SCH) lasers with ZnMgSSe cladding and ZnSSe guiding layers were deposited on GaAs substrates. X-ray diffraction (reciprocal space mapping), photoluminescence (PL) at 14–300K, PL excitation, and optical pumping experiments were performed. The quantum wells show a high luminescence efficiency up to room temperature. Optical pumping experiments were carried out at various temperatures (77, 300–375K) and excitation densities using a nitrogen laser. The lasing threshold could be determined to be less than 20 kW/cm² at 77K, and even room temperature lasing was observed at an excitation density which was below 200 kW/cm².     

Controlled Growth of ZnO Nanowires and Their Optical Properties

This article surveys recent developments in the rational synthesis of single‐crystalline zinc oxide nanowires and their unique optical properties. The growth of ZnO nanowires was carried out in a simple chemical vapor transport and condensation (CVTC) system. Based on our fundamental understanding of the vapor–liquid–solid (VLS) nanowire growth mechanism, different levels of growth controls (including positional, orientational, diameter, and density control) have been achieved. Power‐dependent emission has been examined and lasing action was observed in these ZnO nanowires when the excitation intensity exceeds a threshold (∼40 kW cm^–2). These short‐wavelength nanolasers operate at room temperature and the areal density of these nanolasers on substrate readily reaches 1 × 10¹⁰ cm^–2. The observation of lasing action in these nanowire arrays without any fabricated mirrors indicates these single‐crystalline, well‐facetted nanowires can function as self‐contained optical resonance cavities. This argument is further supported by our recent near‐field scanning optical microscopy (NSOM) studies on single nanowires.     

A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N′‐Ditridecyl Perylene Diimide Based Field‐Effect Transistors: Improving Performance and Stability with Thermal Treatment

A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO₂ gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO₂ gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm² V^?1 s^?1 in the 20 V saturation regime and long‐term stability with respect to H₂O/O₂ degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.     

Low threshold,room temperature pulsed and quasi-continuous lasing in optically pumped CdZnTe/ZnTe quantum wells

We report room temperature optically pumped lasing with a threshold of 6 kW/ cm² in a CdZnTe/ZnTe multiple quantum well. Quasi-continuous optically pumped lasing at room temperature has also been achieved. We discuss the influence of composition on mode confinement and show that the lowest thresholds are expected in samples in which the active layer is slightly zinc-rich compared to the cladding layers.     

Solution‐Processed Low Threshold Vertical Cavity Surface Emitting Lasers from All‐Inorganic Perovskite Nanocrystals

Recently, newly engineered all‐inorganic cesium lead halide perovskite nanocrystals (IPNCs) (CsPbX₃, X = Cl, Br, I) are discovered to possess superior optical gain properties appealing for solution‐processed cost‐effective lasers. Yet, the potential of such materials has not been exploited for practical laser devices, rendering the prospect as laser media elusive. Herein, the challenging but practically desirable vertical cavity surface emitting lasers (VCSELs) based on the CsPbX₃ IPNCs, featuring low threshold (9 µJ cm^?2), directional output (beam divergence of ≈3.6°), and favorable stability, are realized for the first time. Notably, the lasing wavelength can be tuned across the red, green, and blue region maintaining comparable thresholds, which is promising in developing single‐source‐pumped full‐color visible lasers. It is fully demonstrated that the characteristics of the VCSELs can be versatilely engineered by independent adjustment of the cavity and solution‐processable nanocrystals. The results unambiguously reveal the feasibility of the emerging CsPbX₃ IPNCs as practical laser media and represent a significant leap toward CsPbX₃ IPNC‐based laser devices.     

Organic Electronics: High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N′‐Ditridecyl Perylene Diimide Based Field‐Effect Transistors: Improving Performance and Stability with Thermal Treatment (Adv. Funct. Mater. 16/2010)

A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO₂ gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO₂ gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm² V^?1 s^?1 in the 20 V saturation regime and long‐term stability with respect to H₂O/O₂ degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.     

Lasing in the vertical direction in InGaN/GaN/AlGaN structures with InGaN quantum dots

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (～ 10⁵ cm^?1) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm².     

Manipulable and Hybridized,Ultralow‐Threshold Lasing in a Plasmonic Laser Using Elliptical InGaN/GaN Nanorods

Manipulating stimulated‐emission light in nanophotonic devices on scales smaller than their emission wavelengths to meet the requirements for optoelectronic integrations is a challenging but important step. Surface plasmon polaritons (SPPs) are one of the most promising candidates for sub‐wavelength optical confinement. In this study, based on the principle of surface plasmon amplification by the stimulated emission of radiation (SPASER), III‐Nitride‐based plasmonic nanolaser with hybrid metal–oxide–semiconductor (MOS) structures is designed. Using geometrically elliptical nanostructures fabricated by nanoimprint lithography, elliptical nanolasers able to demonstrate single‐mode and multimode lasing with an optical pumping power density as low as 0.3 kW cm^?2 at room temperature and a quality Q factor of up to 123 at a wavelength of ≈490 nm are achieved. The ultralow lasing threshold is attributed to the SPP‐coupling‐induced strong electric‐field‐confinement in the elliptical MOS structures. In accordance with the theoretical and experimental results, the size and shape of the nanorod are the keys for manipulating hybridization of the plasmonic and photonic lasing modes in the SPASER. This finding provides innovative insight that will contribute to realizing a new generation of optoelectronic and information devices.     

Low threshold melt-processed two-photon organic surface emitting upconversion lasers

Herein, a low threshold, wavelength-tunable, compact, two-photon pumped upconversion laser is presented. The surface emitting lasers are composed of melt-processed 1,4-bis[2-[4-[N,N-di(p-totyl)amino]phenyl]vinyl]benzene (DADSB) as active media and two designed distributed bragg reflectors. The melting fabrication process is very simple, and the lasing threshold is as low as 150 μJ cm^?2 pulse^?1, when pumped by a Ti:sapphire amplifier operating at 800 nm with a 150 fs pulse width. To the best of our knowledge, it is one of the lowest values for two-photon lasers. Lasing from multimode to single-mode oscillation is demonstrated. Tunable single mode oscillation was obtained at wavelength from 514 nm to 523 nm with a spectral width of less than 0.2 nm.