Amplified Spontaneous Emission Properties Research Articles

Optimized dual-band amplified spontaneous emission properties of PFO and BUBD-1 blend films based on AgNPs doped buffer layers

Dual-band amplified spontaneous emission (ASE) can be used as a spectral analysis technique to detect specific chemical or biological molecules. In this paper, the dual-band ASE properties of blend films containing a small organic molecule N,N’-(4,4′-(1E,1′E)-2, 2′-(1,4-phenylene) bis(ethene-2,1-diyl)) −bis(4,1-phenylene))-bis(2-ethyl-6-methyl-phenylaniline) (BUBD-1) and a conductive polymer Poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) were investigated and optimized. As the doping concentration of BUBD-1 in the PFO was increased from PFO: 1 wt% BUBD-1 to PFO: 5 wt% BUBD-1, the ASE emission wavelength shifted from single- to dual-band and then back. The dual-band ASE performance of the blend film was also improved by introducing a Poly(methyl methacrylate) (PMMA) buffer layer containing silver nanoparticles (AgNPs), which resulted in a significant decrease in the excitation energy threshold of both ASE peaks and a significant increase in the net gain. Due to the LSPR effect of AgNPs, the ASE thresholds for peaks at 460 nm (PFO) and 490 nm (BUBD-1) in the blend film decreased from 12.24 ± 0.49 μJ/pulse to 6.99 ± 0.28 μJ/pulse and from 12.75 ± 0.51 μJ/pulse to 7.03 ± 0.28 μJ/pulse, respectively. The experimental and theoretical simulation demonstrated that the incomplete energy transfer between PFO and BUBD-1 led to a dual-band ASE effect. In addition, the enhanced light absorption, emission, and scattering caused by LSPR in the AgNPs improved the threshold and gain for dual-band ASE. This provides a possibility of realizing dual-band organic semiconductor lasers.

Low‐Threshold Amplified Spontaneous Emission of Dion–Jacobson‐Phase Perovskite Films Achieved by Tuning Diamine Cation Size

Dion–Jacobson (DJ)‐phase perovskites have received attention in the field of amplified spontaneous emission (ASE) and lasers due to their excellent structural stability and charge‐transfer performance. However, the effect of the diamine cation size on the ASE properties of DJ‐phase perovskite has not been studied. Herein, the effect is systematically studied and in the results it is shown that tuning the size of the diamine cation can inhibit the formation of the small‐n phases, reduce the surface roughness, and passivate defects of DJ‐phase perovskite films. Based on those, the low‐threshold ASE (61 μJ cm−2 under nanosecond laser excitation) of the 1,3‐propylenediamine‐cation‐based DJ‐phase perovskite films is realized. Additionally, the film exhibits excellent photostability. The ASE intensity remains at 90% of the original value after a pulsed laser irradiation of 3000 μJ cm−2 for 120 min. In this work, a strategy is provided to realize high‐performance DJ‐phase perovskite ASE and lasers.

Investigation of the Amplified Spontaneous Emission Threshold of Cesium Lead Bromide Perovskite Quantum Dots at Different Excitation Wavelengths

The goal of this research is to see how excitation wavelength affects steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and amplified spontaneous emission (ASE) in CsPbBr3 perovskite quantum dots (PQD). At PL and ASE, a plausible mechanism for explaining the excitation wavelength-dependent phenomena was proposed. The PL and ASE properties of CsPbBr3 PQD as optical materials were examined experimentally at excitation wavelengths of 355–450 nm. An optical parametric amplifier system was used to accomplish optical pumping utilizing a laser pulse with a pulse duration of 70 ps. The ASE threshold was explored and compared the ratio of photons in the pump pulse to band gap energies. The excitation wavelength (λ ex) has a considerable influence on the ASE behavior, with high optical densities correlating to optimal excitation, as evidenced by the absorption spectrum, which has a larger absorption coefficient. Furthermore, the energy density at the ASE threshold was closely correlated with the λ ex following the absorption spectrum. Also, it has been demonstrated that changing the excitation wavelength reduces the PQD PL lifetime. Finally, electron-hole pairs can be produced at a reasonable depth from the film’s surface using the appropriate excitation wavelength.

Studies of the transition between amplified spontaneous emission and optical lasing in ultrahigh-Q polymeric micro-pedestals.

In this work, we demonstrate the properties of Rhodamine B-doped polymeric cylindrical microlasers to perform either as gain amplification devices through amplified spontaneous emission (ASE) or as optical lasing gain devices. A study based on different %wt concentrations of microcavity families with distinct geometrical features demonstrates the characteristic dependence on either gain amplification phenomena. Principal component analysis (PCA) discriminates the relationship between the main ASE and lasing properties and the geometrical aspects of the cavity families. ASE and optical lasing thresholds were found, respectively, as low as 0.2 μJcm-2 and 0.1 μJcm-2 passing the best-reported microlaser performances in literature for cylindrical cavities, even in comparison with those based on 2D patterns. Moreover, our microlasers showed ultrahigh Q-factor of ∼3 × 106, and for the first time, to the best of our knowledge, a visible emission comb constituted by above a hundred peaks at 40 μJcm-2 with a registered free spectral range (FSR) of 0.25 nm corroborated through the whispery gallery mode (WGM) theory.

Effect of surface ligand density on the amplified spontaneous emission properties of CsPbI2Br quantum dots

In recent years, amplified spontaneous emission (ASE) properties of all-inorganic perovskite quantum dots have attracted the interest of many researchers. Here, CsPbI2Br quantum dots (QDs) were synthesized by the hot injection method, and the effect of the purification process on the ASE properties of QDs has been investigated. In the purification process, n-hexane and ethyl acetate (EtOAc) are used as solvent and antisolvent, respectively. The results show that the volume ratio of n-hexane vs EtOAc has a remarkable effect on the optical performance. When the volume ratio is 1:5, the QDs have a larger size which increases the light scattering and absorption cross-section, thus achieving the lowest ASE threshold of 0.301 mJ/cm2. This work not only provides a facile strategy to obtain a low threshold of CsPbI2Br QDs but also enriches the application prospects of perovskite lasers.

High-performance all-inorganic CsPbBr3 quantum dots with a low-threshold amplified spontaneous emission.

All-inorganic halide perovskite CsPbX3(X = Br/Cl/I)quantum dots have gained a considerable attention in the optoelectronic fields. However, the high cost and poor stability of the prepared CsPbX3 quantum dots (QDs) are inevitable challenges for their future practical applications. And the high-performance CsPbX3 QDs are always needed. Herein, a facile and low-cost synthesis scheme was adopted to prepare the CsPbBr3 QDs modified by lead bromide (PbBr2) and tetraoctylammonium bromide (TOAB) ligands at room temperature in open air. The prepared CsPbBr3 QDs exhibited a high photoluminescence quantum yield (PLQY) of 96.6% and a low amplified spontaneous emission (ASE) threshold of 12.6 µJ/cm2. Stable ASE intensity with little degradation was also realized from the CsPbBr3 QDs doped with PMMA. Furthermore, the enhanced ASE properties of the CsPbBr3 QDs-doped PMMA based on distributed feedback (DFB) substrate was achieved with a lower threshold of 3.6 µJ/cm2, which is 28.6% of that of the (PbBr2 + TOAB)-treated CsPbBr3 QDs without PMMA. This work exhibits a promising potential in the on-chip light source.

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.

Dependence of amplified spontaneous emission threshold of BUBD-1 thin films on molecular orientation

The dependence of the amplified spontaneous emission (ASE) threshold on molecular orientation in vacuum deposited BUBD-1 films was investigated with the plane waveguide structure. The molecular orientations measured by the variable angle spectroscopic ellipsometry and the angular-dependent p-polarized PL spectra were optimized by varying the substrate temperature during deposition. Both of the optimized ASE threshold and the gain factor were obtained at the substrate temperature of 75 °C. The lowest ASE threshold of 3.3 μJ/pulse is only one third of that at 30 °C. The maximized net gain factor of 10.55 cm−1 is 1.7 times higher than that of 6.11 cm−1 at 30 °C. The enhancement of ASE performance of BUBD-1 film was ascribed to the lower horizontal ratio and surface roughness, which increased the total reflection and decreased the light scattering of light emission in the thin film light waveguide. It is an efficient way to optimize the molecular dipole orientation to enhance the ASE properties.

The differentiation procedure between amplified spontaneous emission and lasing phenomena

The lasing process emerges from an amplified spontaneous emission (ASE) when an optical resonator is present. The ASE is often observed during the laser emission, especially in random lasing studies. The differentiation between ASE and random lasing is difficult, particularly considering coherent and incoherent random lasing from polymeric dye-doped systems. In this article, we present the straightforward procedure of differentiation of both processes, in order to simultaneously designate the ASE and lasing emission properties and performance.

Near‐Infrared Lasing in Four‐Zigzag Edged Nanographenes by 1D versus 2D Electronic π‐Conjugation

AbstractThe search of compounds emitting in the near‐infrared (NIR) has been accelerated owing to their use in biomedical and telecommunications applications. In this regard, nanographenes (NGs) are attractive materials adequate for integration with other technologies, which have recently demonstrated amplified spontaneous emission (ASE) and lasing across the visible spectrum. Here, the optical and ASE properties of four‐zigzag edged NGs of the [m,n]peri‐acenoacene family are reported, whose size is increased through conjugation extension by varying n (from 3 to 5) while keeping m = 2. Results show that such 1D conjugation extension method is more efficient in terms of shifting the photoluminescence (PL) to the infrared (PL at 710 nm in the larger compound, PP‐Ar) than through 2D conjugation extension as in previously reported NGs (PL at 676 nm with the largest compound FZ3, with n = 3 and m = 4). Additionally, PP‐Ar shows dual‐ASE (at 726 and 787 nm), whose origin is elucidated through Raman and transient absorption spectroscopies. These compounds’ potential for red and NIR lasing is demonstrated through the fabrication of distributed feedback lasers with top‐layer resonators. This study paves the way towards the development of stable low‐cost all‐plastic NIR lasers.

Amplified spontaneous emission in thin films of quasi-2D BA3MA3Pb5Br16 lead halide perovskites.

Quasi-2D (two-dimensional) hybrid perovskites are emerging as a new class of materials with high photoluminescence yield and improved stability compared to their three-dimensional (3D) counterparts. Nevertheless, despite their outstanding emission properties, few studies have been reported on amplified spontaneous emission (ASE) and a thorough understanding of the photophysics of these layered materials is still lacking. In this work, we investigate the ASE properties of multilayered quasi-2D BA3MA3Pb5Br16 films through the dependence of the photoluminescence on temperature and provide a novel insight into the emission processes of quasi-2D lead bromide perovskites. We demonstrate that the PL and ASE properties are strongly affected by the presence, above 190 K, of a minor fraction of the high temperature (HT) phase. This phase dominates the PL spectra at low excitation density and strongly affects the ASE properties. In particular, ASE is only present between 13 K and 230 K, and, at higher temperatures, it is suppressed by absorption of charge transfer states of the HT phase. Our results improve the understanding of the difficulties to obtain ASE at room temperature from these quasi-2D materials and are expected to guide possible materials improvement in order to exploit their excellent emission properties also for the realization of low threshold optically pumped lasers.

The analysis of amplified spontaneous emission and luminescence enhancement of BUBD-1 based on host-guest system

The lowest amplified spontaneous emission (ASE) threshold (1.51 μJ/pulse) of CBP: 2 wt%BUBD-1 blend films was about 6 times lower than that of BUBD-1 neat film (9.25 μJ/pulse). The OLEDs with blend film as the emission layer (EML) exhibited an excellent photoelectric performance. In this regard, a series of theoretical analysis were carried out to explain the enhancement of ASE and luminescence performance of BUBD-1 in different aspects. Except for the reducing concentration quenching, a higher Stokes shift, energy transfer efficiency and radiation attenuation rate (kr) happened in the blend films. Moreover, the molecular dipole orientation of EML films at the interface and in thin films were analyzed based on the second-harmonic generation (SHG) method and angle-dependent PL spectra analysis. We find that not only the molecular dipole orientation angle alters in the blend film relative to the neat film, but also the angle is different when the films deposited with different methods. Based on the calculated molecular dipole orientation angle, we propose that the varied dipole angle in the blend film contributed to the device properties too. Our works provide a theory insight into the enhancement of ASE and luminescence properties based on host-guest system.

Single-Source Thermal Evaporation Growth and the Tuning Surface Passivation Layer Thickness Effect in Enhanced Amplified Spontaneous Emission Properties of CsPb(Br0.5Cl0.5)3 Perovskite Films.

High-quality inorganic cesium lead halide perovskite CsPb(Br0.5Cl0.5)3 thin films were successfully achieved through evaporation of the precursors and deposition sequentially by a single-source thermal evaporation system. The different melting points of the precursors were enabled us to evaporate precursors one by one in one trip. The resulting films through its fabrication were smooth and pinhole-free. Furthermore, this technique enabled complete surface coverage by high-quality perovskite crystallization and more moisture stability oppositely of that produce by solution-processed. Then the perovskite films were encapsulated by evaporated a polymethyl methacrylate (PMMA) polymer as a specialized surface passivation approach with various thicknesses. The blue emission, high photoluminescence quantum yield (PLQY), stable, and low threshold of amplified spontaneous emission (ASE) properties of CsPb(Br0.5Cl0.5)3 films in the bulk structure at room temperature were achieved. The effects of the surface-passivation layer and its thickness on the optical response were examined. Detailed analysis of the dependence of ASE properties on the surface passivation layer thickness was performed, and it was determined this achieves performance optimization. The ASE characteristics of bare perovskite thin film were influenced by the incorporation of the PMMA with various thicknesses. The improvement to the surface layer of perovskite thin films compared to that of the bare perovskite thin film was attributed to the combination of thermal evaporation deposition and surface encapsulation. The best results were achieved when using a low PMMA thickness up to 100 nm and reducing the ASE threshold by ~11 μJ/cm2 when compared with free-encapsulation and by ~13 μJ/cm2 when encapsulation occurs at 200 nm or thicker. Compared to the bare CsPb(Br0.5Cl0.5)3, ASE reduced 1.1 times when the PMMA thickness was 100 nm.

Cocrystallization Tailoring Multiple Radiative Decay Pathways for Amplified Spontaneous Emission.

Amplified spontaneous emission (ASE) is intrinsically associated with lasing applications. Inefficient photon energy transfer to ASE is a long-standing issue for organic semiconductors that consist of multiple competing radiative decay pathways, far from being rationally regulated from the perspective of molecular arrangements. Herein, we achieve controllable molecular packing motifs by halogen-bonded cocrystallization, leading to ten times increased radiative decay rate, four times larger ASE radiative decay selectivity and thus remarkable ASE threshold decrease from 223 to 22 μJ cm-2 , albeit with a low photoluminescence quantum yield. We have made an in-depth investigation on the relationship among molecular arrangements, vibration modes, radiative decay profiles and ASE properties. The results suggest that cocrystallization presents a powerful approach to tailor the radiative decay pathways, which is fundamentally important to the development of organic ASE and lasing materials.

Radiative energy transfer assisted amplified spontaneous emission in asymmetric-coupled-waveguide structures

We demonstrate the efficient amplified spontaneous emission (ASE) of rhodamine 640 in asymmetric-coupled-waveguides. In these structures, two active waveguides, one doped with [2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) and the other with rhodamine 640, are coupled by a passive layer of polyvinyl alcohol. Under a suitable pumping wavelength of 500 nm, the DCM waveguiding layer acts as the donor and rhodamine waveguiding layer acts as the acceptor. Time-resolved fluorescence measurements are employed to confirm that radiative energy transfer is the responsible mechanism for ASE when the waveguiding layers are separated by a thickness of less than 50 nm. In this case, the ASE threshold was found to be reduced by a factor of 16, associated with an intensity enhancement of 56 times, compared to that of the rhodamine waveguiding layer. Next, we investigate the ASE properties of asymmetric-coupled-waveguides as a function of coupling layer thickness. The thickness-dependent coupling constant is simulated using the coupled-mode theory, and its behavior is applied to understand the experimental results.

Determination of the Best Empiric Method to Quantify the Amplified Spontaneous Emission Threshold in Polymeric Active Waveguides.

Amplified Spontaneous Emission (ASE) threshold represents a crucial parameter often used to establish if a material is a good candidate for applications to lasers. Even if the ASE properties of conjugated polymers have been widely investigated, the specific literature is characterized by several methods to determine the ASE threshold, making comparison among the obtained values impossible. We quantitatively compare 9 different methods employed in literature to determine the ASE threshold, in order to find out the best candidate to determine the most accurate estimate of it. The experiment has been performed on thin films of an homopolymer, a copolymer and a host:guest polymer blend, namely poly(9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-cobenzothiadiazole) (F8BT) and F8BT:poly(3- hexylthiophene) (F8BT:rrP3HT), applying the Variable Pump Intensity (VPI) and the Variable Stripe Length (VSL) methods. We demonstrate that, among all the spectral features affected by the presence of ASE, the most sensitive is the spectral linewidth and that the best way to estimate the ASE threshold is to determine the excitation density at the beginning of the line narrowing. We also show that the methods most frequently used in literature always overestimate the threshold up to more than one order of magnitude.

Donor-Acceptor Type Pendant Conjugated Molecules Based on a Triazine Center with Depressed Intramolecular Charge Transfer Characteristics as Gain Media for Organic Semiconductor Lasers.

A set of fluorene-capped pendant conjugated molecules (T-m and T-p), which consist of a triazine center with three carbazole substituents as the donor-acceptor (D-A) type pendant structure, were designed, synthesized, and investigated as gain media for organic semiconductor lasers (OSLs). In particular, varying the capping positions of the fluorene units on the pendant core structures results in significantly different intramolecular charge transfer (ICT) properties, where T-m manifested depressed ICT characteristic and high fluorescence quantum yield. The lowest amplified spontaneous emission (ASE) threshold in neat films was recorded as 1.9 μJ cm-2 for T-m and 83.8 μJ cm-2 for T-p, which indicated that the depressed ICT characteristics in the case of T-m help to enhance the ASE properties. Remarkably, the ASE threshold remained almost unchanged and the ASE spectra showed very small shifts (within 1 nm) for T-m with film samples annealed up to 180 °C in open air. In contrast, its linear counterpart 2FEtCz-m showed a clearly increased ASE threshold upon annealing above 100 °C. The results suggest that the selective construction of conjugated pendant molecules with depressed ICT characteristics is beneficial for finely modulating the optical and electrical properties as well as improving the thermostability and photostability, which manifests the great potential as a robust gain media for OSLs.

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.

Charge Carrier Dynamics and Broad Wavelength Tunable Amplified Spontaneous Emission in ZnxCd1-xSe Nanowires.

ZnxCd1-xSe is regarded as a promising semiconducting material for optoelectronic devices. However, the tunable amplified spontaneous emission (ASE) properties and corresponding charge carrier recombination dynamics in ZnxCd1-xSe (0 ≤ x ≤ 1) nanowires (NWs) remain poorly understood. Herein, the charge carrier dynamics and ASE properties in ZnxCd1-xSe NWs were systematically investigated. In these NWs, the one/two-photon pumped ASE wavelength across the entire visible spectrum (480-725 nm) can be easily tuned via compositional engineering. The ASE threshold is closely related to the absorption coefficient and PL lifetime. At room temperature, free-carrier recombination is dominated in the low fluence pumped PL process. The ASE behavior is determined by exciton recombination in the high pump fluence (>1018 cm-3) region. These findings uncover the origin of the tunable PL/ASE properties in ZnxCd1-xSe NWs and establish them as having practical application as a series of lasing gain materials.

Simultaneous retrieval of optical gains, losses, and threshold in active waveguides

The generation of Amplified Spontaneous Emission (ASE) is routinely used to assess the performance of active materials prior to developing thin film lasers. The Variable Stripe Length method has been profusely used for decades to measure the optical gain in these materials and devices, but experimental and theoretical evidences cast doubts upon its reliability. With the advent of an ever increasing number of solution-processed laser compounds that can be implemented as low-cost, flexible, and/or integrated devices, there is now more than ever a need to develop an alternative and trustful method to delineate all their amplifying signatures. Herein, a new formalism to fully characterize the ASE properties, based on the most frequent Variable Pump Intensity method, is reported. An analytical expression taking into account the most relevant spatiotemporal and photophysical effects has been found that can be fitted to ASE spectra. This expression allows retrieving, from a single ASE experiment, the spectrally resolved losses coefficient and net optical gains at all pump values, as well as to calculate, instead of visually finding, the ASE threshold. The reported formalism serves as a tool to categorize the best candidates for a given laser application through a reliable, robust, time-saver, and standardized methodology.