Amplified Spontaneous Emission Peak Research Articles

Linearly Manipulating Color Emission via Anion Exchange Technology for High Performance Amplified Spontaneous Emission of Perovskites.

The most attractive advantages of all-inorganic cesium lead halide perovskites are their optical gain over broad spectral ranges through the visible spectrum, so are well suited to use in tunable lasers or broadband amplifiers. Most reported anion exchange reactions face a challenge to achieve the desired halogen-variable perovskites due to rapid and uncontrollable reactions and difficulty to synthesize directly. In this study, a simple vapor/solid anion exchange strategy is demonstrated for controlling the reaction process and realizing a wide range tuning of band gap and amplified spontaneous emission (ASE) wavelength, which exhibits a temperature-dependent anion exchange rate. By optimizing the reaction temperature at 90°C, the ASE wavelength can be linearly manipulated by just controlling the reaction time. A clear quantitative relationship between ASE peak position and reaction time is achieved. Compares with the CsPbClBr2 film obtained via the liquid phase anion exchange method, the fabricated perovskite films obtained by vapor/solid anion exchange technology exhibit superior film quality and enhanced ASE performance. This work may have applications in the future using facile and controllable techniques to develop high-quality full-color visible lasers.

Room temperature amplified spontaneous emissions in a sub-centimeter sized CsPbBr3 bulk single crystal.

All inorganic perovskite CsPbBr3 shows great potential in laser device because of its excellent luminescence characteristics, while the room temperature amplified spontaneous emission (ASE) in a large size CsPbBr3 bulk single crystal is still quite difficult. Herein, we have obtained the room temperature ASE in a sub-centimeter size CsPbBr3 bulk single crystal pumped with the single-photon excitation. Based on the reproducible light path within the CsPbBr3 bulk single crystal, the photonic feedback between the bottom and top facets naturally enhances the population inversion, which exhibits an amplified spontaneous emission threshold of ∼320 µJ/cm2. The blue shift of the ASE peak along with the increased pumping intensity is also observed and ascribed to the reduction of the refractive index and the energy band filling effect. These findings demonstrate the sub-centimeter size CsPbBr3 bulk single crystal to be an excellent candidate as an optical gain media for crystal lasers.

Optical gain properties of interfacial material PFN-Br and its application potentials in future electrically pumped organic lasers

In this paper, the optical gain properties of the 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)]) (PFN-Br) and its potential applications in future electrically pumped organic lasers are revealed and systematically studied. To the best of our knowledge, no studies on the optical gain properties of PFN-Br or its prototype, poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] have been reported before. These conjugated polyelectrolytes are widely used as the interlayers in organic light emitting diodes or organic solar cells. The thickness of such an interlayer is usually less than 10 nm, which is considered not sufficient for supporting light waveguiding. Therefore, the thickness of the PFN-Br layer used in this work is increased to more than 100 nm. Through careful study, the polymer is found to possess a low threshold of amplified spontaneous emission (ASE) (~11 μJ/cm<sup>2</sup>) and a small ASE cutoff thickness (<50 nm). It is an efficient blue emission (~456 nm) gain medium. The ASE peak of the PFN-Br film is red-shifted as the thickness increases from 50 to 220 nm. By utilizing the great resistance of PFN-Br against the organic solvent, such as toluene, PFN-Br/F8BT bilayer devices on quartz and PFN-Br/MEH-PPV bilayer devices on ITO glass are fabricated and characterized. In the PFN-Br/F8BT bilayer devices, it is found that the PFN-Br interlayer has very limited influence on F8BT. The ASE threshold of F8BT increases only twice, compared with that of F8BT monolayer device, when 100-nm-thick PFN-Br layer is introduced beneath the F8BT film. No significant change in optical gain or loss is observed. Most of the extra losses in F8BT due to the introduction of PFN-Br are attributed to the larger refractive index of PFN-Br than that of quartz substrate. Furthermore, in the PFN-Br/MEH-PPV bilayer devices on ITO glass, introducing PFN-Br interlayer resulting in optimal ASE performance of MEH-PPV compared with that on bare ITO surface. The ASE threshold of MEH-PPV is reduced as much as 60% (from 402 μJ/cm<sup>2</sup> to 160 μJ/cm<sup>2</sup>) while the PFN-Br layer is sandwiched between ITO and MEH-PPV. The PFN-Br layer modifies the waveguiding modes, and reduces the interaction between excitons and ITO electrodes. As a result, the ASE performance of MEH-PPV is improved. The findings of this report indicate that the PFN-Br is not only a good carrier transport material but also a highly-efficient gain medium. PFN-Br, combined with its advantages in different fields, is expected to play various roles in future organic electrically pumped lasers.

Synthesis, Crystal Structures, and Nonlinear Optical Properties of Chalcone Doped by Titanium Dioxide Nanoparticles for Solar Cell Application

In this work, we investigate the effects of titanium dioxide (TiO2) nanoparticle percentages on the optical and electrical properties of 3-(4-(dimethyl-amino)phenyl)-1-phenyl-(2E)-propen-1-one (DAAP). In order to achieve thin films, DAAP was dissolved in acetone and doped with different ratios of TiO2. The pure and composite mixtures were spin-coated onto a glass substrate. We investigated the influence of TiO2 on XRD patterns, absorption, energy band gaps, refractive indices, sheet resistance, resistivity, and Hall coefficients. We used the XRD technique to study the structure of DAAP pre- and post-doping with TiO2 nanoparticles. It was evident from the XRD patterns that the composite transformed from an amorphous to a polycrystalline nature and behaved similarly to titanium oxide crystals. The pure sample exhibited an absorption band of 409 nm. With the addition of TiO2, the whole absorption spectrum shifted to the blue region. For example, with a dopant percentage of 15%, the spectrum shifted to a wavelength of 368 nm. The energy band gap values increased with a dopant concentration from 2.65 eV of pure DAAP to 2.91 eV of maximum dopant percentage (15%). The refractive index decreased to its lowest value of 2.47 with the increase in TiO2 concentration. The impact of increasing TiO2 percentage highly improved electrical characteristics by reducing the sheet resistance and resistivity to 905 k(Ω/sq) and 230 k on the (Ω · cm), respectively. An optimized DAAP doped with 15% TiO2 has been used as an n-type layer on a p-type monocrystalline silicon wafer (Si (111)) to fabricate η = 0.23% efficient solar cells. On the other hand, the amplified spontaneous emission (ASE) of the DAAP and dopant mixture was excited by the third harmonic generation (λex = 355 nm). The pure DAAP exhibits an ASE peak at 535 nm. The intensity decreased rapidly with increased dopant concentration, whereas the full width at half-maximum (FWHM) increased slightly.

Amplified Spontaneous Emission from Zwitterionic Excited-State Intramolecular Proton Transfer.

The unique four-level photocycle characteristics of excited-state intramolecular proton transfer (ESIPT) materials enable population inversion and large spectral separation between absorption and emission through their respective enol and keto forms. This leads to minimal or no self-absorption losses, a favorable feature in acting as an optical gain medium. While conventional ESIPT materials with an enol-keto tautomerism process are widely known, zwitterionic ESIPT materials, particularly those with high photoluminescence, are scarce. Facilitated by the synthesis and characterization of a new family of 2-hydroxyphenyl benzothiazole (HBT) with fluorene substituents, HBT-Fl1 and HBT-Fl2, we herein report the first efficient zwitterionic ESIPT lasing material (HBT-Fl2). The zwitterionic ESIPT HBT-Fl2 not only shows a remarkably low solid-state amplified spontaneous emission (ASE) threshold of 5.3 μJ/cm2 with an ASE peak at 609 nm but also exhibits high ASE photostability. Coupled with its substantially large Stokes shift (≈236 nm ≈10,390 cm-1) and an extremely small overlap of excited-state absorption with ASE emission, comprehensive density functional theory (DFT) and time-dependent DFT studies reveal the zwitterionic characteristics of HBT-Fl2. In opposition to conventional ESIPT with π-delocalized tautomerism as observed in analogue HBT-Fl1 and parent HBT, HBT-Fl2 instead shows charge redistribution in the proton transfer through the fluorene conjugation. This structural motif provides a design tactic in the innovation of new zwitterionic ESIPT materials for efficient light amplification in red and longer-wavelength emission.

Investigation of Threshold Carrier Densities in the Optically Pumped Amplified Spontaneous Emission of Formamidinium Lead Bromide Perovskite Using Different Excitation Wavelengths

The high crystal quality of formamidium lead bromide perovskite (CH(NH2)2PbBr3 = FAPbBr3) was infiltrated in a mesoporous TiO2 network. Then, high-quality FAPbBr3 films were evaluated as active lasing media, and were irradiated with a picosecond pulsed laser to demonstrate amplified spontaneous emission (ASE), which is a better benchmark of its intrinsic suitability for gain applications. The behavior was investigated using two excitation wavelengths of 440 nm and 500 nm. Due to the wavelength-dependent absorbance spectrum and the presence of a surface adsorption layer that could be reduced using the shorter 440 nm wavelength, the ASE power dependence was strongly reliant on the excitation wavelength. The ASE state was achieved with a threshold energy density of ~200 µJ/cm2 under 440 nm excitation. Excitation at 500 nm, on the other hand, needed a higher threshold energy density of ~255 µJ/cm2. The ASE threshold carrier density, on the other hand, was expected to be ~4.5 × 1018 cm−3 for both excitations. A redshift of the ASE peak was detected as bandgap renormalization (BGR), and a BGR constant of ~5–7 × 10−9 eV cm was obtained.

Solid‐State Red Laser with a Single Longitudinal Mode from Carbon Dots

AbstractMiniaturized solid‐state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red‐emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High‐concentration doping alters the CDs’ emission from blue to red, while the electron‐donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs’ ASE peak, was constructed. Combining the CDs and microcavity produced a solid‐state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal‐to‐noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid‐state micro/nano lasers with potential use in practical photonics.

Solid-State Red Laser with a Single Longitudinal Mode from Carbon Dots.

Miniaturized solid-state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red-emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High-concentration doping alters the CDs' emission from blue to red, while the electron-donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs' ASE peak, was constructed. Combining the CDs and microcavity produced a solid-state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal-to-noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid-state micro/nano lasers with potential use in practical photonics.

Mixed Halide Perovskite Films by Vapor Anion Exchange for Spectrally Stable Blue Stimulated Emission.

Solution-processed all-inorganic CsPbX3 perovskites exhibit outstanding optoelectronic properties and are being considered as a promising optical gain medium, with impressive performance in the green and red region. However, the development of CsPbX3 for blue emission is still lagging far behind, owing to difficulties in thin films synthesis and spectral instability subject to light irradiation. Here, a facile vapor anion exchange (VAE) method that enables preparation of blue-emitting perovskite films with both excellent surface morphology and good photo-stability is reported. The mixed-Br/Cl quasi-2D perovskite films show spectrally stable pure blue emission (471nm) under continuous-wave laser irradiation with power density as high as 81Wcm-2 . Furthermore, optically pumped blue amplified spontaneous emission (ASE) is realized based on the mixed-Br/Cl perovskite films. By changing the duration of VAE treatment, the ASE peak can be tuned from 537nm down to 475nm. This work not only presents a facile method to prepare high quality mixed halide Cs-based perovskite films, but also pave the way for further exploration of stable blue perovskite lasing.

Ultralow Threshold Optical Gain Enabled by Quantum Rings of Inverted Type‐I CdS/CdSe Core/Crown Nanoplatelets in the Blue

AbstractAchieving low‐threshold optical gain for solution‐processed materials is crucial for their real‐life applications and deployment as gain media. However, the realization of low gain threshold in the blue region has shown to be technically an extremely challenging task using colloidal nanocrystals as a result of fast nonradiative Auger rates in smaller nanocrystals. Here, ultralow‐threshold blue amplified spontaneous emission (ASE) (≈2.7 µJ cm−2) accompanied with a large net modal gain coefficient of 360 cm−1 in the blue enabled by blue‐emitting (≈455–465 nm) colloidal quantum rings (QRs) of inverted type‐I CdS/CdSe core/crown nanoplatelets (NPLs) is proposed and demonstrated. The synthesized QRs with controlled crown size outperform the best reported ASE thresholds and net modal gain coefficients from the solution‐processed materials by ≈2.5‐ and ≈4‐fold, respectively, in the similar blue spectral window. Utilizing this QR architecture, it is also shown that the ASE peak can be spectrally tuned by controlling the lateral size of the crown and hence quantum confinement in the lateral direction. These outstanding results support the prospects of these solution‐processed QRs made of 2D hetero‐NPLs in the challenging blue region as colloidal gain.

Thickness-Tunable Self-Assembled Colloidal Nanoplatelet Films Enable Ultrathin Optical Gain Media.

We propose and demonstrate construction of highly uniform, multilayered superstructures of CdSe/CdZnS core/shell colloidal nanoplatelets (NPLs) using liquid interface self-assembly. These NPLs are sequentially deposited onto a solid substrate into slabs having monolayer-precise thickness across tens of cm2 areas. Because of near-unity surface coverage and excellent uniformity, amplified spontaneous emission (ASE) is observed from an uncharacteristically thin film having 6 NPL layers, corresponding to a mere 42 nm thickness. Furthermore, systematic studies on optical gain of these NPL superstructures having thicknesses ranging from 6 to 15 layers revealed the gradual reduction in gain threshold with increasing number of layers, along with a continuous spectral shift of the ASE peak (∼18 nm). These observations can be explained by the change in the optical mode confinement factor with the NPL waveguide thickness and propagation wavelength. This bottom-up construction technique for thickness-tunable, three-dimensional NPL superstructures can be used for large-area device fabrication.

Wavelength tuning of amplified spontaneous emission through onchip control of the droplet size

Wavelength tunable amplified spontaneous emission (ASE) based on dye-doped ‘unconventional microdroplets’ which do not support the whispering gallery modes is demonstrated using a microfluidic chip. A tunability of around 18 nm in the wavelength of ASE is achieved by tweaking the size and shape of the droplets through controlling the pressure given to the chip, thus by modifying the flow rate of the liquid through the channel. The shift in ASE peak wavelength observed upon changing the droplet configuration is attributed to the concentration-dependent redshift exhibited by the dye molecules. This assumption is confirmed by observing a blueshift in emission peak after reducing the region of illumination of the chip, thereby reducing the number of dye molecules under the illumination region. Also, the droplet configuration consisting of the largest droplets have shown around 270 times enhancement in the peak intensity at 3 mJ pump energy, and around 20% reduction in threshold compared to the stream of smallest possible droplets.

Spectral and ASE properties of an amino chalcone 1-phenyl-3-[4-(1-pyrrolidinyl) phenyl]-(2E)-propen-1-one

This work demonstrates the spectral and amplified spontaneous emission (ASE) properties of a new chalcone laser dye material of 1-phenyl-3-[4-(1-pyrrolidinyl) phenyl]-(2E)-propen-1-one (4-Pone) for the first time. The absorption, fluorescence, Stokes’ shift and quantum yield were obtained using different organic solvents. The energy band gap was calculated and compared with that of 3-[4-(dimethylamino) phenyl]-1-phenyl-(2E)-propen-1-one (DMAPPP). Under suitable concentrations and pump power excitation (Nd: YAG laser 355 nm), 4-Pone produced an intense ASE at 534 nm. Previously, we had reported that DMAPPP showed optical activities that were significantly better than that of coumarin 503. The results revealed that both chalcones had close fluorescence spectra; nevertheless, the absorption spectra were red-shifted for 4-Pone. Under pulsed laser excitation (Nd: YAG laser λex = 355 nm), 4-Pone produced an ASE peak at 535 nm. The most important feature is that 4-Pone has a low concentration threshold for laser action.

Restraining effect of film thickness on the behaviour of amplified spontaneous emission from methylammonium lead iodide perovskite

The authors report amplified spontaneous emission (ASE) behaviour from methylammonium lead iodide (CH 3 NH 3 PbI 3 ) perovskite films of different thicknesses. The ASE threshold carrier density noticeably decreased with thickness, indicating the existence of different traps with perovskite films of smaller thicknesses. We attribute this behaviour to the presence of surface states, whose origin can result from different practical fabrication steps with samples of small thicknesses. The ASE threshold carrier density increased from 3.29 × 10 18 cm -3 at a film thickness of 650 nm to 7.73 × 10 18 cm -3 at a film thickness of 80 nm. This work warns that while decreasing the film thickness is of practical importance to reduce the ASE threshold pump current, e.g. in electrically driven light-emitting diodes, the solution processing of perovskites, newly re-discovered for their potential photonic and photovoltaic applications, can be a restraining factor. Band gap renormalisation (BGR) is also observed in the prepared films as a redshift in the ASE peak with increasing the pump power, and the BGR coefficient is estimated to be ~ 6.3 × 10 -8 eV cm.

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

Electrically pumped organic lasing requires the integration of electrodes contact into the laser cavity in an organic light‐emitting diode (OLED) or organic field effect transistor configuration to enable charge injection. Efficient and balanced carrier injection requires in turn alignment of the energy levels of the organic active layers with the Fermi levels of the cathode and anode. This can be achieved through chemical substitution with specific aromatic functional groups, although paying the price for a substantial (and often detrimental) change in the emission and light amplifying properties of the organic gain medium. Here, using host–guest energy transfer mixtures with hosts bearing a systematic and gradual shift in molecular orbitals is proposed, which reduces the amplified spontaneous emission (ASE) threshold of the organic gain medium significantly while leaving the peak emission unaffected. By virtue of the low guest doping required for complete host‐to‐guest energy transfer, the injection levels in the blends are attributed to the host whereas the gain properties solely depend on the guest. It is demonstrated that the ASE peak and thresholds of blends with different hosts do not differ while the current efficiency of OLEDs devices is deeply influenced by molecular orbital tuning of the hosts.

Influence of solvents on the amplified spontaneous emission characteristics of LD-423

Influence of the solvent environments, pumping pulse energies and concentrations on the spectral properties of 1,2,3,8-tetrahydro-1,2,3,3,5-pentamethyl-7H-pyrrolo[3,2-g]quinolin-7-one (LD-423) have been investigated. The photophysical characteristics such as absorption, fluorescence spectra, Stokes’ shift, fluorescence quantum yield, absorption, emission cross sections, extinction coefficient and amplified spontaneous emission (ASE) were measured. Here, LD-423 showed two ASE in a certain organic solution under pulsed laser excitation (Nd: YAG λex = 355 nm). One of these peaks corresponds to the fluorescence, while the other peak is an anomalous peak which does not have a corresponding fluorescence peak. This abnormal ASE peak can be ascribed to the fact that the excited molecules are connected in the excited state and the solvent acts as a link between them.

Temperature Dependence of the Amplified Spontaneous Emission from CsPbBr3 Nanocrystal Thin Films

Cesius lead halide perovskite colloidal nanocrystals are among the most promising perovskite systems for light-emitting devices applications due to their high fluorescence quantum yield and high optical gain at room temperature. In this letter, we report on the first investigation of temperature dependence of amplified spontaneous emission (ASE) properties of thin films of CsPbBr3 nanocrystals. We demonstrate that ASE is strongly temperature-dependent, with a complex variation in temperature of the ASE intensity, threshold, and peak wavelength. The joint investigation of the photoluminescence (PL) spectra below and above the ASE threshold allows us to conclude that the temperature increase results in the formation of disordered subdomains emitting in the low-energy tail of the PL spectra, leading to the existence of three emission regimes with transitions at about 90 and 170 K, with individually different temperature dependences.

A highly sensitive chemosensor for solution based on organic semiconductor laser gain media

Laser has been widely applied in the scientific and engineering areas including communications, medical treatment, industry, and military due to its extremely strict monochromaticity, high coherence and high energy density. Organic laser based on solution processable polymer gain media has attracted considerable attention in various applications due to its easy fabrication, compact system and flexibility. At present, the chemosensors based on organic semiconductor laser have been widely developed. It has been reported to achieve solution monitoring by organic DFB (distributed feedback) laser. Although the method has its own advantages, there are still many operability and craftsmanship problems to be resolved. In this paper we introduce a new type of the real-time monitoring for various solution. The monitor is realized by using amplified spontaneous emission (ASE) from optically pumped organic semiconductor gain media. The gain media comprising blends of poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(3-hexylthiophene) (P3HT) at a ratio of 15:85 wt.% is dissolved into toluene (25 mg/mL). Thin films (90 nm thickness) of P3HT/F8BT are obtained by spin coating (2000 rpm) from solution onto pre-cleaned quartz substrates. The P3HT/F8BT film demonstrates the absorption peak at 471 nm, the PL peak at 622 nm, and the ASE peak at 661 nm with FWHM (full-width-at-half-maximum) linewidth of ～ 10 nm under the stripe laser pumping. The thin films are, then, covered by droplet of solution to form planar waveguide structure with variable effective refractive index. Upon analyte binding, a change in refractive index at the P3HT/F8BT film surface results in a change in the effective refractive index of the planar waveguide and in turn induces shift of the ASE mode wavelength and variation of ASE threshold of the organic gain media. The changes in ASE wavelength and threshold can be monitored for sensing. The red shift of 4.5 nm in the ASE spectrum is from 661 to 665.5 nm and the threshold increases from 0.579 J/pulse to 1.447 J/pulse which can be detected with the concentration of sodium chloride increasing from 0 to 25 wt.% in pure water. Our experimental results show that this method is easy to detect the concentration grads of 1 wt.% sodium chloride solution. The measurement sensitivity of solution reaches 97.8 nm/RIU (refractive index unit), and accuracy reaches 141.9 nm/RIU. Furthermore, we demonstrate that the chemosensor could be used for detecting different kinds of solution in the same concentration. The ASE peak position and threshold display clearly different when the droplet 10 wt.% sodium, chloride solution and hydromel solution onto P3HT/F8BT film. Our study suggests that the organic gain media films have potentiality to be developed as a high sensitivity and high accuracy chemosensor to detect solution due to the high sensitivity of the ASE peak position and threshold to the refractive index of the solution.

Mono- to few-layered graphene oxide embedded randomness assisted microcavity amplified spontaneous emission source

The realization of optoelectronic devices using two-dimensional materials such as graphene and its intermediate product graphene oxide (GO) is extremely challenging owing to the zero band gap of the former. Here, a novel amplified spontaneous emission (ASE) system based on a GO-embedded all-dielectric one-dimensional photonic crystal (1DPhC) micro-resonator is presented. The mono- to few-layered GO sheet is inserted within a microcavity formed by two 5-bilayered SiO2/SnO2 Bragg reflectors. Significantly enhanced photoluminescence (PL) emission of GO embedded in 1DPhC is explicated by studying the electric field confined within the micro-resonator using the transfer matrix method. The inherent randomness, due to fabrication limitations, in the on-average periodic 1DPhC is exploited to further enhance the PL of the optically active micro-resonator. The 1DPhC and randomness assisted field confinement reduces the ASE threshold of the mono- to few-layered weak emitter making the realization of an ASE source feasible. Consequently, ASE at the microcavity resonance and at the low-frequency band-edge of photonic stop-band is demonstrated. Variation of the detection angle from 5° to 30°, with respect to the sample surface normal allows reallocation of the defect mode ASE peak over a spectral range of 558–542 nm, making the GO-incorporated 1DPhC a novel and attractive system for integrated optic applications.

High power amplified spontaneous emission from an oligomer in solution

The laser action from a conductive oligomer 9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene (HOTF) has been demonstrated in this study. First absorption spectra were studied for HOTF in benzene under a wide range of concentrations. The spectra showed that there was only one peak at 355nm under a wide range of concentrations indicating the absence of dimerization. The fluorescence spectra for low concentrations showed two peaks, at 390nm and 410nm, which could be attributed to the monomer and the excimer. At higher concentrations, the peak at 390nm almost vanished and the dominant peak was at 410nm with a hump at 435nm. Laser action was tested in a transverse pumping configuration where the conducting oligomer was pumped by laser pulses from the third harmonic of an Nd:YAG laser (355nm). It could be seen that there were two amplified spontaneous emission (ASE) peaks, at 390 and 410nm. These peaks could be attributed to the monomer and excimer of the HOTF oligomer; but, even after our best efforts, we were not able observe the ASE peak at 435nm corresponding to the hump in the fluorescence spectra. The power of ASE and the photo-chemical stability were remarkably high. This trend for the oligomer is entirely different from its conjugated polymer counterpart poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO). This is perhaps the first report on ASE from an excimeric state of the conjugated oligomer HOTF in liquid solution.