Spontaneous Emission Properties Research Articles

Optical and Amplified Spontaneous Emission Properties of 4H-Pyran-4-Ylidene-2-Cyanoacetate Fragment Containing 2-Cyanoacetic Acid Derivative in PVK, PSU, or PS Matrix

Organic solid-state lasers are highly promising devices known for their low-cost fabrication processes and compact sizes and the tunability of their emission spectrum. These lasers are in high demand across various industries including biomedicine, sensors, communications, spectroscopy, and military applications. A key requirement for light-emitting materials used in a light-amplifying medium is a low threshold value of the excitation energy of the amplified spontaneous emission (ASE). A newly synthesized non-symmetric red-light-emitting laser dye, Ethyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-tert butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTB), has shown great promise in meeting this requirement. KTB, with its attached bulky trityloxyethyl groups, has the ability to form amorphous thin films from a solution using a wet-casting method. Recent experiments have demonstrated that KTB exhibits a low ASE threshold value. This study focused on investigating the optical and amplified spontaneous emission properties of KTB in poly(N-vinylcarbazole) (PVK), polysulfone (PSU), and polystyrene (PS) matrices at various concentrations. The results showed that as the concentration of the dye increased, a redshift of the photoluminescence and ASE spectra occurred due to the solid-state solvation effect. The lowest ASE threshold value of 9 µJ/cm2 was achieved with a 20 wt% concentration of KTB in a PVK matrix, making it one of the lowest excitation threshold energies reported to date.

Multifunctional BiOCl: Sm3+ nanophosphors: A luminescent platform for solid-state lighting applications, optical thermometry, photocatalytic and forensic applications

Rare earth-activated phosphor materials have been widely used as active probes in optical materials for multidimensional applications. Here, we report a series of ultrahigh purity orange-red emitting BiOCl: xSm3+ (x= 0.5- 2.5 mol %) nanophosphors synthesized via conventional solid-state method at relatively low temperatures for various photonic and forensic applications. XRD and Rietveld refinement results confirmed the tetragonal crystal structure of the synthesized phosphor materials with space group P4/nmm. Fourier transform infrared (FT-IR) and Raman spectroscopy were used to perform the functional group analysis. The UV-Vis-NIR spectra were analyzed to determine the Judd-Ofelt (JO) intensity parameters (Ω2, Ω4, Ω6) and to identify the bonding structure and spontaneous emission properties of the samples. The prepared phosphors exhibit intense orange-red emission under 408 nm excitation and beyond 1 mol% doping of Sm3+ ions, the emission intensity decreases due to concentration quenching mechanism via, dipole-dipole interaction between the optically active Sm3+ ions in the phosphor sample. The synthesized BiOCl: Sm3+ nanophosphors possess low correlated color temperature (CCT), admirable high color purity (99.4%) and outstanding internal quantum efficiency (IQE) of 95.27%. The optical thermometry behavior of the optimized sample has been investigated in detail. Moreover, the optimized nanophosphor stains on porous and non-porous surfaces show clear ridge patterns with high sensitivity, efficiency, and minimal background hindrance for latent fingerprints and lip print detection in forensic applications and are used as security ink in anti-counterfeiting applications. Overall, the results revealed the potential prospects of BiOCl: Sm3+ nanophosphors in the field of display applications, optical thermometry, and forensic sciences.

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.

End Cap Effect on Solution-Processable Deep Blue Lasing Materials with Low-Amplified Spontaneous Emission Thresholds.

Organic lasers have attracted increasing attention owing to their superior characteristics such as lightweight, low-cost manufacturing, high mechanical flexibility, and high emission-wavelength tunability. Recent breakthroughs include electrically pumped organic laser diodes and an electrically driven organic laser, integrated with an organic light-emitting diode pumping. However, the availability of efficient deep blue organic laser chromophores remains limited. In this study, we develop two novel rigid oligophenylenes, end-capped with carbazole and phenylcarbazole groups, to demonstrate exceptional optical and amplified spontaneous emission (ASE) properties. These oligophenylenes are not only solution processable but also exhibit remarkably high solution photoluminescence quantum yields (PLQYs) of 90% and high radiative rates of 1.35 × 109 s-1 in the deep blue range. Our theoretical calculations confirm that the carbazole and phenylcarbazole end groups play a pivotal role in enhancing the optical transitions of the oligophenylene laser chromophores, thereby elevating their emission oscillator strengths. Remarkably, these materials demonstrate low solid-state ASE threshold values of 1.0 and 1.5 μJ/cm2 (at 431 and 418 nm, respectively). To the best of our knowledge, these ASE thresholds represent the lowest reported at these specific ASE wavelengths in the literature, regardless of whether they are solution-processed or thermally evaporated films. Furthermore, they exhibit excellent thermal and photostability, low triplet quantum yields, as well as negligible overlap of excited-state absorption within the ASE emission region, making them excellent candidates for a new class of deep blue materials for organic lasers. By integrating insights from theoretical calculations and experimental validation, our study provides a comprehensive understanding of the design principles behind these high-performing organic laser chromophores, paving the way for the development of advanced organic lasers with enhanced performance characteristics.

Polymeric laser rods based on modified poly(methyl methacrylate) matrix synthesized by FeIII complex catalyzed atom transfer radical polymerization with enhanced optical gain and Photostability

AbstractThe investigation of fabricating ultra‐compact solid‐state dye laser (SSDL) using N'N‐dimethylformamide (DMF) modified poly(methyl methacrylate) (PMMA) as the polymeric matrix was carried out. Atom transfer radical polymerization (ATRP) was introduced to manipulate the polymerization process of PMMA. By adjusting the additive amount of the FeIII complex (mixture of FeCl3 and 2,2’‐Bipyridyl (bPy)), the polymerization degree of PMMA was coordinated to gain better amplified spontaneous emission (ASE) properties of the embedded laser dye, Lumogen Orange 240 (LO). The ASE threshold of the FeIII complex catalyzed sample decreased as high as ~75%, from 225.3 ± 11.2 μJ cm−2 to 57.2 ± 2.9 μJ cm−2, comparing to that measured in common PMMA matrix. Additionally, a secondary dye, Stilbene 420 was added in the system for sharing excess excitation energy and oxidization damage, to overcome the photostability problem caused by the oxygen‐rich solvent, DMF. The operational lifetime of the resulted sample increased 200%, to the similar level of that without DMF component. Finally, by mechanical polishing and coating a thin film of silver at one end of the PMMA rod, an analogous Fabry‐Perot resonator was structured within the rod. Decent laser emission was obtained from the resulted SSDL without complex external cavities.

Quasi‐CW Amplified Spontaneous Emission in Air‐Processed Quasi‐2D Perovskite Thin Films with High Stability

AbstractDue to the hydrophobic organic cations, quasi‐two‐dimensional (quasi‐2D) lead halide perovskite materials have shown better moisture resistance. However, the inappropriate multiphase structure in the quasi‐2D perovskite films seriously affects the efficient transport of energy from low‐n domains to high‐n domains, especially when prepared in air. Herein, the study develops efficient quasi‐2D perovskite films in 30% ± 10% humidity and studies their amplified spontaneous emission (ASE) properties. It can be seen that the phase disproportionation of the quasi‐2D perovskite films prepared in air is greatly suppressed by manipulating the crystallization kinetics of the multiphase structure via using the organic additive benzimidazole (BI), thereby enabling a narrowed phase distribution. Due to the improvement in energy transfer efficiency, surface roughness, and humidity stability, the ASE with a low threshold of 13.4 µJ cm−2 is realized under the quasi‐continuous pumping condition, which is significantly <28.8 µJ cm−2 of the pristine film. Furthermore, the introduction of BI organic additive enhanced the number of peak intensity half‐decay pulses to as high as 5.6 × 107, indicating a good operating stability of the BI‐treated films. This work suggests that the BI‐treated quasi‐2D perovskite films provide the possibility for preparing high‐performance lasers in air.

Broadband 1.5-2.1 µm emission in gallo-germanate dual-core optical fiber co-doped with Er3+ and Yb3+/Tm3+/Ho3.

The near-infrared emission in fabricated low-phonon energy, gallo-germanate glass, and double-core optical fiber has been investigated. Broadband amplified spontaneous emission (ASE) was obtained in optical fiber with cores doped with: 1st - 0.2Er2O3 and 2nd - 0.5Yb2O3/0.4Tm2O3/0.05Ho2O3 as a result of the superposition of emission bands from both cores corresponding to the Er3+:4I13/2→4I15/2 (1st core) and Tm3+:3F4 → 3H6/Ho3+:5I7 → 5I8 (2nd core) transitions. The effect of fiber length and pump wavelength on the near-infrared amplified spontaneous emission (ASE) properties has been analyzed for 1 m and 5 m optical fiber. The widest emission bandwidth (355 nm - 3 dB level) was obtained for a 5 m length optical fiber pumped by a 940 nm laser.

Photonic Modulation Enabled by Controlling the Edge Structures of Boron‐Doped Molecular Carbons

AbstractControl over topological edges of molecular carbons (MCs) is of importance for achieving diverse molecular topologies and desirable physical properties. However, it remains very challenging for heteroatom‐doped MCs due to the synthetic difficulty. Herein, we report control over the edge structures of boron‐doped MCs (BMCs) via the sequential cyclization strategy. Three BMC molecules that feature the C56B2 or C84B2 polycyclic π‐skeletons with selective cove/fjord or cove/bay edges, respectively, were synthesized through the rational combination of Mallory photoreaction and Scholl reaction. We not only obtain the largest boron‐doped π‐system reported so far, but also disclose that fine control of their edges and length greatly affects electronic structures and thereby photonic properties of BMCs, such as tunable aromaticity, decreased band gaps, as well as redshifted absorptions and fluorescence. Remarkably, the C56B2 molecule exhibits stimulated emission behavior and amplified spontaneous emission property, both of which have never been reported for pristine boron‐doped π‐systems, thus demonstrating the potential of BMCs as optical gain materials for laser cavities.

Photonic Modulation Enabled by Controlling the Edge Structures of Boron-Doped Molecular Carbons.

Control over topological edges of molecular carbons (MCs) is of importance for achieving diverse molecular topologies and desirable physical properties. However, it remains very challenging for heteroatom-doped MCs due to the synthetic difficulty. Herein, we report control over the edge structures of boron-doped MCs (BMCs) via the sequential cyclization strategy. Three BMC molecules that feature the C56 B2 or C84 B2 polycyclic π-skeletons with selective cove/fjord or cove/bay edges, respectively, were synthesized through the rational combination of Mallory photoreaction and Scholl reaction. We not only obtain the largest boron-doped π-system reported so far, but also disclose that fine control of their edges and length greatly affects electronic structures and thereby photonic properties of BMCs, such as tunable aromaticity, decreased band gaps, as well as redshifted absorptions and fluorescence. Remarkably, the C56 B2 molecule exhibits stimulated emission behavior and amplified spontaneous emission property, both of which have never been reported for pristine boron-doped π-systems, thus demonstrating the potential of BMCs as optical gain materials for laser cavities.

Mixing Dion–Jacobson and Ruddlesden–Popper Structures in Quasi‐2D Perovskite Films for Thermal‐ and Photo‐Stable Stimulated Emission

AbstractQuasi‐two–dimensional (2D) perovskite films are promising candidates as a gain medium for stimulated emission owing to their hydrophobicity and efficient energy funneling that facilitates the population inversion. However, the commonly used Ruddlesden–Popper (R–P) perovskites still suffer from instability induced by high‐density pumping as well as the resulting heating effect. Here, quasi‐2D perovskite films with mixed Dion–Jacobson (D–J) and R–P phases are demonstrated with both excellent amplified spontaneous emission (ASE) properties and thermal‐ and photo‐stabilities under ambient conditions. In these films, octyl ammonium bulky organic cations are used to obtain the preferred crystal orientation and highly smooth surface for low‐threshold ASE, while 1,8‐octanedi ammonium cations contribute to the greatly improved stability. The films containing the D–J phase exhibit good structural stability even after 130 °C heat treatment for 48 h. The mixed‐ligands film maintains a low ASE threshold of 11.6 µJ cm−2 and a high optical gain of 413 cm−1 after environmental annealing. It is demonstrated that it is the diammonium that firmly bonds to the perovskite layer,allowing the maintenance of quasi‐2D perovskite structure and good ASE performances.

Air-sensitive amplified spontaneous emission in lecithin-capped CsPbBr3 nanocrystals thin films

Fully inorganic lead halide perovskite nanocrystals (NCs) are receiving great attention as active materials for photonic and optoelectronic devices. While the lack of long-term stability, due to their sensitivity to ambient air exposure, currently prevents their application to commercial devices, the presence of reversible environmental effects opens the way for possible applications of lead halide perovskites in resistive or optical sensors. In this work we investigate the Amplified Spontaneous Emission (ASE) properties and their dependence on the surrounding environment of lecithin-capped CsPbBr3 NCs thin films. We demonstrate low ASE threshold under nanosecond pumping, both in air and in vacuum, with emission intensity lower in air than in vacuum. We also show that the emission quenching induced by ambient air exposure, ascribed to moisture-induced surface solvation, is reversible and it is fully restored by a suited vacuum stint application. The ASE sensitivity is up to 6.5 larger than the spontaneous emission one, making lecithin-capped CsPbBr3 NCs thin films promising systems for the development of optical humidity sensors with high sensitivity.

Competition of Carrier Kinetics Contributes to Amplified Spontaneous Emission in Quasi-2D/3D (PBA)2MAn–1PbnBr3n+1 Thin Films under Strip Light Mode

Quasi-2D halide perovskites have potential in lasing due to their amplified spontaneous emission (ASE) properties. The ASE of (PBA)2MAn-1PbnBr3n+1 thin films has been confirmed by photoluminescence (PL) testing using stripe light excitation (SLE). The ASE threshold decreases with decreasing environmental temperature (TE) or increasing number of inorganic layers (n). Using the transient absorption technique, the Auger recombination and the cooling process of the high-activity carrier are accelerated with the decrease of n or TE. A new ASE mechanism is proposed where high-activity carriers directly emit photons under photon perturbation from adjacent sites, leading to the accumulation and amplification of emitted photons only in the SLE region for ASE to occur. In addition, the reduction of n promotes light scattering between nano-thin layers, which supports a rapid increase in the ASE signal after the ASE threshold is crossed.

Aprotic Solvent Effect in Preparation of Organo Lead Iodide Perovskite Nanowires by Two-Step Spin-Coating Procedure

Lead-iodide perovskite (CH3NH3PbI3 ≡ MAPbI3) nanowires (NWs) were prepared by a two-step spin-coating technique by modifying one of the perovskite precursors with a small amount of aprotic solvent. In the two-step spin-coating technique, the perovskite precursors are MAI and PbI2. The first MAI powder is dissolved in isopropanol (IPA) to produce an isopropanol-MAI solution, while the second PbI2 is used in N, N-dimethylformamide (DMF) as an aprotic solvent. Here, a small amount of DMF was used with an IPA solution of MAI to grow 1D NWs based on MAPbI3 perovskite. Then, the film was formed directly from the MAPbI3 perovskite nanowires (PNWs) by coating the PbI2 layer with an IPA solution of MAI modified by DMF. The amount of DMF in the MAI/IPA solution was adjusted in the range between 0 and 50 μl. One-dimensional (1D) PNWs (∼100 nm diameter) and three-dimensional (3D) perovskite nanocrystals are compared. The structural and optical properties of the PNWs films are systematically investigated using X-ray diffraction patterns (XRD), scanning electron microscopy images (SEM), UV–vis absorption, and photoluminescence (PL). The result is that the presence of an additional solvent and its optimized amount in the MAI/IPA solution can increase the length and efficiency of charge transfer by facilitating perovskite transformation, as evidenced by the intensity of PL and the formation of a high-quality perovskite film. Compact, hole-free films with low trap states (crystal defects) were obtained. Further investigation of the lead iodide perovskite showed that reducing the dimensionality from 3D to 1D resulted in shorter wavelengths of the absorption edge and the PL peak in both the absorption and PL spectra. The shorter wavelengths indicate more localized exciton states in NWs. Finally, the amplified spontaneous emission (ASE) properties were obtained under picosecond laser excitation and a low ASE threshold was found at 10 and 53 μJ/cm2 for 1D and 3D, respectively, at about 300 nm film thickness.

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.

Temperature-Dependent Amplified Spontaneous Emission in CsPbBr3 Thin Films Deposited by Single-Step RF-Magnetron Sputtering.

Due to their high optical efficiency, low-cost fabrication and wide variety in composition and bandgap, halide perovskites are recognized nowadays as real contenders for the development of the next generation of optoelectronic devices, which, among others, often require high quality over large areas which is readily attainable by vacuum deposition. Here, we report the amplified spontaneous emission (ASE) properties of two CsPbBr3 films obtained by single-step RF-magnetron sputtering from a target containing precursors with variable compositions. Both the samples show ASE over a broad range of temperatures from 10 K up to 270 K. The ASE threshold results strongly temperature dependent, with the best performance occurring at about 50 K (down to 100 µJ/cm2), whereas at higher temperatures, there is evidence of thermally induced optical quenching. The observed temperature dependence is consistent with exciton detrapping up to about 50 K. At higher temperatures, progressive free exciton dissociation favors higher carrier mobility and increases trapping at defect states with consequent emission reduction and increased thresholds. The reported results open the way for effective large-area, high quality, organic solution-free deposited perovskite thin films for optoelectronic applications, with a remarkable capability to finely tune their physical properties.

Spontaneous emission from Λ-type three-level atom driven by bichromatic field in anisotropic double-band photonic crystals

The spontaneous emission property of Λ-type three-level atom driven by the bichromatic field in the anisotropic double-band photonic crystal is calculated by n-times iteration method. The influence of different parameters on atomic spontaneous emission is studied, and the phenomena of atomic spontaneous emission are explained in the dressed state representation. It is found that the spontaneous emission spectra of the atom driven by the bichromatic field presents a multi-peak comb structure. The position of the emission peak is determined by the initial state of the atom, and the interval between the neighboring emission peaks is the detuning δ of the bichromatic field. When the ratio between Rabi frequency intensity and the detuning δ of the bichromatic field remains unchanged, the intensity of each emitted peak remains invariant. The spontaneously emitted peak can be annihilated in the band gap and enhanced near the band edge in the anisotropic photonic crystals. Meanwhile, we also observe the fluorescence quenching phenomenon in the spontaneous emission spectra. The research in this paper provides the theoretical guidance for the control of atomic spontaneous emission.

Low threshold amplified spontaneous emission and lasing from single crystals and polymer microspheres based on a blue aggregation-enhanced emission molecule

Organic semiconductors as a gain medium have attracted much attention in organic lasers due to their unique properties, i.e., large stimulated emission cross section, widely tunable spectrum region, and mechanical flexibility. Aggregation-caused quenching broadly exists in amorphous solid films and single crystals, which result in high threshold. Here, we studied amplified spontaneous emission (ASE) and lasing properties of an aggregation-enhanced emission (AEE) molecule, namely, 2PB-AC, who owns high photoluminescence quantum efficiency in a solid film and a single crystal. The grown long rod-like single crystals exhibited very good ASE characteristics with a threshold of 48 μJ cm−2 and a full width at half-maximum (FWHM) of 8.4 nm. Furthermore, when forming polymer microspheres by a surface tension-induced self-assembly method, a low lasing threshold of 0.32 mJ cm−2 and a FWHM of 0.41 nm were also obtained well, and their lasing modes could be modulated by changing the diameter of the microspheres. The investigations on transient photoluminescence dynamics and femtosecond transient absorption analysis demonstrated that the high radiative decay rate and the well separation between a stimulated emission band and an excited state absorption band are the main reasons of good lasing performance, indicating that AEE molecules are promising lasing materials.

Achieving Low Threshold and High Optical Gain Amplified Spontaneous Emission in MAPbI3 Perovskite Films via Symmetric Waveguide Effect

AbstractLead halide perovskites are attractive light source candidates for new amplifiers and lasers in the growing field of short‐distance data communication. However, the presence of plenty of defects and poor stability are the major obstacle to the production and application of perovskite optoelectronic devices. Three strategies are proposed to prepare MAPbI3 perovskite films with high stability and enhanced light amplification in this study: 1) MAPbI3 films are prepared with ionic liquid methylammonium acetate (MAAc) to improve the quality of the films; 2) a poly(methyl methacrylate) (PMMA) passivation layer is used to improve the optical and thermal stability of the MAPbI3 film; 3) a symmetric waveguide (SWG) structure is designed to enhance the amplified spontaneous emission (ASE) properties of the MAPbI3 film. The formed SWG exhibits increased mode confinement and reduced propagation loss, thus enabling a lower ASE threshold, a higher optical gain and improved photostability, thermal and humidity stability compared with the pristine MAPbI3 film. Femtosecond transient absorption spectroscopy and electric field distribution calculation are utilized to elucidate the carrier dynamics and carrier‐phonon effect and the microscopic origin of the observed effects of functionalization. This study indicates the possibility of simple and effective approaches for realizing efficient ASE and lasing.

Ultrafast resonant exciton-plasmon coupling for enhanced emission in lead halide perovskite with metallic Ag nanostructures.

Integrating metal halide perovskites onto plasmonic nanostructures has recently become a trending method of enabling superior emissive performance of perovskite nanophotonic devices. In this work, we present an in-depth study on the spontaneous emission properties of hybrid systems comprising CsPbBr3 nanocrystals and silver nanostructures. Specifically, a 5.7-fold increment of the photoluminescence (PL) intensity and a 1.65-fold enhancement of the PL relaxation rate is attained when the transition energy of CsPbBr3 is spectrally resonant with the oscillational frequency of Ag nanodisks (NDs), which is attributed to the intense exciton-plasmon coupling-induced Purcell effect. Furthermore, a 540-fs ultrafast energy transfer from the CsPbBr3 excitons to Ag plasmons is revealed by femtosecond pump-probe experiments, suggesting the key mechanism responsible for the Purcell-enhanced radiative emission. Our finding offers a unique understanding of the enhanced emissive behavior in the plasmon-coupled perovskite system and paves the way for further applications.

Amplified Spontaneous Emission Threshold Dependence on Determination Method in Dye-Doped Polymer and Lead Halide Perovskite Waveguides.

Nowadays, the search for novel active materials for laser devices is proceeding faster and faster thanks to the development of innovative materials able to combine excellent stimulated emission properties with low-cost synthesis and processing techniques. In this context, amplified spontaneous emission (ASE) properties are typically investigated to characterize the potentiality of a novel material for lasers, and a low ASE threshold is used as the key parameter to select the best candidate. However, several different methods are currently used to define the ASE threshold, hindering meaningful comparisons among various materials. In this work, we quantitatively investigate the ASE threshold dependence on the method used to determine it in thin films of dye-polymer blends and lead halide perovskites. We observe a systematic ASE threshold dependence on the method for all the different tested materials, and demonstrate that the best method choice depends on the kind of information one wants to extract. In particular, the methods that provide the lowest ASE threshold values are able to detect the excitation regime of early-stage ASE, whereas methods that are mostly spread in the literature return higher thresholds, detecting the excitation regime in which ASE becomes the dominant process in the sample emission. Finally, we propose a standard procedure to properly characterize the ASE threshold, in order to allow comparisons between different materials.