Superfluorescence (SF) is a cooperative quantum emission process characterized by intense, ultrafast bursts of light, with promising applications in quantum photonics. In solid-state systems, SF typically requires cryogenic conditions, with quasi-2D hybrid metal halide perovskites being a notable exception where room-temperature SF has been reported. However, the mechanisms enabling high-temperature SF in these materials remain poorly understood, and the distinction between SF and amplified spontaneous emission (ASE) is often overlooked. Here, SF in hybrid quasi-2D perovskite phenylbutylammonium cesium lead bromide (PBA:CsPbBr3) is reported with the lowest threshold fluence recorded to date in perovskites, observed across 78-180 K. The phase behavior of emission under varying temperature and excitation fluence is mapped, identifying transitions between SF, ASE, and spontaneous emission regimes. A simple ab-initio model has been developed to predict the emission density, correlation, and trace distance for understanding the cooperative phenomena and the unified theory of SF and ASE. The analysis reveals the underlying dynamics that differentiate cooperative from non-cooperative emission, offering new insight into light-matter interactions in perovskites. These findings deepen the understanding of SF in solid-state systems and inform the design of quantum optical materials operable at elevated temperatures.

Unravel the impacts of deep-level defects on Auger recombination in nanocrystals for realizing low-threshold blue amplified spontaneous emission

Spontaneous emission controlled by the twisted α-MoO3 bilayers

Quantum hydrodynamic theory modeling of spontaneous emission and energy level shift in plasmonic nanostructures: Impact of energy functional choices

ABSTRACT Hybrid organic–inorganic perovskites have emerged as promising gain media for coherent light sources, yet defect‐mediated losses and phase instability limit their practical applications. Here, we synergistically integrate triple‐cation compositional engineering (Cs 0.05 FA 0.85 MA 0.1 PbI 3 ) with piperazine hydroiodide (PI) bifunctional molecular passivation to achieve ultralow‐threshold near‐infrared amplified spontaneous emission (ASE). Structural analyses reveal that this dual strategy suppresses PbI 2 impurities, enlarges grain sizes, and reduces surface roughness. Optical characterization demonstrates photoluminescence enhancement and reduced Urbach energy, confirming effective defect passivation. Under 532 nm excitation, PI‐treated film exhibits a record‐low ASE threshold of 1.05 µJ cm −2 . Besides, a 1.7‐fold higher net gain (143.8 cm −1 ) and 65.8% reduced optical loss (1.15 cm −1 ) are also observed compared with the Control film. Furthermore, femtosecond transient spectroscopy results indicate prolonged optical gain lifetimes (762 ps vs. 468 ps). Power‐dependent time‐resolved photoluminescence analysis shows that PI‐treated perovskite films exhibit a lower trap‐assisted monomolecular recombination constant and an increased bimolecular recombination constant, which is responsible for the enhancement of its radiative recombination efficiency and thereby the significantly positive role in promoting ASE. Meanwhile, the passivated triple‐cation perovskite films can maintain an ultra‐stable ASE output. This work establishes an effective strategy for designing high‐performance perovskite lasers through synergistic compositional and interfacial optimization.

Quasi-two-dimensional (quasi-2D) Dion-Jacobson (DJ)-type perovskites have recently received growing attention in photoelectronics for their excellent photophysical properties. However, the uncontrollable nature of the crystallization process increases the density of defect states, constraining further improvement in device efficiency. In this study, we investigated the phase distribution, energy transfer, and Auger recombination in quasi-2D perovskite HDAD(FA0.8Cs0.2)4Pb5Br16 thin films through additive methods. The results demonstrate that the incorporation of EABr enhances the radiative recombination efficiency of DJ-type perovskites. More importantly, we realized green amplified spontaneous emission and single-mode vertical-cavity surface-emitting lasing with low thresholds of 8.5 and 12.67 μJ/cm2, respectively. This study presents an approach for fabricating high-performance green lasers.

Two-dimensional colloidal nanoplatelets of cadmium selenide demonstrate significant absorption cross sections and homogeneously broadened band-edge transitions, making them highly useful for a variety of optoelectronic applications. We investigated the temperature dependence of amplified spontaneous emission (ASE) in nanoplatelets that are 4- and 5-monolayers thick. Our findings reveal that the ASE threshold for close-packed (neat) films decreases by a factor of 2–10 as the temperature decreases from ambient levels. This reduction is attributed to both extrinsic factors, such as trapping, and intrinsic factors, like phonon-derived line width.Interestingly, when pump intensities exceed the ASE threshold, we observed the emergence of intense, lower-energy emission at film temperatures of ≤200 K. In contrast, for nanoplatelets dispersed in an inert polymer, both biexcitonic ASE and low-energy emission are suppressed. This suggests that the phenomena observed in neat films depend on high chromophore density and rapid, collective processes. Transient emission spectra show ultrafast red-shifting over time for the lower-energy emission.Collectively, these findings suggest a previously unreported process of amplified stimulated emission from polyexciton states, consistent with the formation of quantum droplets and indicative of an exciton condensate. In the samples studied, quantum droplets form when approximately 17 meV or less of thermal energy is available, which we hypothesize is related to polyexciton binding energy. Polyexciton ASE can result in pump-fluence-tunable, red-shifted ASE, reaching energy levels up to 120 meV lower than biexciton ASE.Our research highlights the crucial role of biexciton and polyexciton populations in nanoplatelets and demonstrates that quantum droplets can achieve light amplification at significantly lower photon energies than biexcitonic ASE.

The properties of neutron excess gallium nuclei are predicted utilizing a single-particle model. The single particle model calculations include alpha, beta, positron, electron capture, and spontaneous fission decay modes. Neutron emission decay modes that have short half-lives are not readily determined by the model. However, estimates of the neutron decay mode were evaluated using the methodology of Chowdhury et al. Using that model, spontaneous neutron emission is predicted to occur in the range of A = 97 – 99. The Japanese Nuclear Data Compilation calculations terminate their calculations at A = 92. Given these results, single-particle model calculations are extended to encompass these values, and were extended to A = 101. Single particle model calculations predict that A = 87 – 101 neutron excess gallium systems form bound systems that have limiting beta decay half-lives in the range of 0.707 – 28.6 ms. Model half-life results for the A = 87 – 92 gallium nuclei are within a factor of about two of the predictions of the Japanese Nuclear Data Compilation calculations.

In this study, we assessed the impact of exposure to scalar coherence fields on the vitality of various organic and inorganic compounds, as measured by their biophoton emission. Samples were irradiated with scalar waves for different exposure durations—30 minutes, 2 days, and 7 days. The results show that prolonged exposure (particularly at 2 and 7 days) maintains or even enhances the intensity of spontaneous photon emission, which serves as an indicator of a high energetic state or sustained vitality.

Ultranarrow emission linewidths and high spectral purity are essential for next-generation displays and advanced optoelectronic/photonic applications. A red photoluminescence (PL) peak with a full width at half-maximum (FWHM) of 3.2nm at 625nm is reported from pure organic π-conjugated 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) self-assembled micro-rods (SAMRs). The sharp PL emission intensifies under prolonged exposure and increased laser power, indicating a photo-brightening (PB) effect. T2T SAMRs are fabricated via thermal annealing of reprecipitated T2T, which facilitates the molecular-scale reorganization of T2T molecules into ordered domains, thereby promoting high-quality π-conjugated crystalline structures. Structural and spectroscopic analyses-including Raman spectroscopy, grazing-incidence wide-angle X-ray scattering, and density functional theory calculations-reveal that the narrow 625nm PL originates from self-trapped excitons (STEs) within an ordered J-aggregated triclinic lattice framework. Additionally, upon PB, a linear increase in STE PL intensity with laser power, along with the prolonged exciton lifetime, is observed for single-stranded T2T SAMRs, which distinguishes STE generation from lasing or amplified spontaneous emission. Remarkably, the emission wavelength remains stable across different laser excitation wavelengths (375, 405, 532nm), heteromolecular systems, and various crystal sizes, underscoring the robustness of the STE state. These findings position T2T SAMRs as promising candidates for high-resolution, high-color-purity red-light sources.

The transient dynamics of electromagnetically induced transparency (EIT) are fundamental to understanding coherent light–atom interactions and the advancement of quantum technologies such as optical switching and quantum memory. However, in room-temperature atomic vapors, Doppler broadening significantly alters these dynamics, yet a comprehensive understanding of its impact on the transient EIT response remains lacking. In this study, we combine analytical and numerical methods to investigate the absorption dynamics of a weak probe field in a three-level Λ-type system driven by a strong coupling field, based on the optical Bloch equations and Laplace transform techniques. Our results show that the transient response is highly sensitive to both the atomic spontaneous emission rate and the Rabi frequency of the coupling field. Increasing the coupling field intensity not only accelerates the approach to steady state but also induces oscillatory dynamics and negative absorption. Under Doppler broadening, the time required to reach steady state increases by approximately three orders of magnitude compared to the Doppler-free case—an effect that is surprisingly insensitive to temperature variations across the 100–400 K range. Moreover, restoring a short steady-state time under broadened conditions necessitates increasing the coupling laser intensity by two orders of magnitude. These findings provide key insights into the influence of Doppler broadening on coherent transient processes and offer practical guidelines for the design of room-temperature atomic devices, including quantum memories and optical modulators.

The amplification and generation of electromagnetic radiation by a rotating metallic or lossy cylinder, first proposed by Zel’dovich in the 1970s, is closely linked to quantum friction, energy extraction from rotating black holes, and runaway mechanisms such as black hole bombs. Although advances such as acoustic analogs of the Zel’dovich effect and the observation of negative resistance in low-frequency electromagnetic models have been reported, genuine positive signal gain, spontaneous emission of electromagnetic waves, and runaway amplification have not previously been verified. Here, we provide the first experimental demonstration that a mechanically rotating metallic cylinder acts as an amplifier of a rotating electromagnetic field mode. Moreover, when combined with a low-loss resonator, the system becomes unstable and operates as a generator seeded only by noise. The exponential runaway amplification of spontaneously generated electromagnetic modes is observed, establishing the electromagnetic analog of the Press-Teukolsky black hole bomb and paving the way to experimental tests of quantum friction from vacuum fluctuations.

Active control of single-photon spontaneous emission out-coupling enhancement by rotation modulation of hyperbolic metamaterials.

Broadband 2 μm amplified spontaneous emission of Er3+/Tm3+/Ho3+ triply-doped germanate glass fiber

Metal halide perovskites offer significant potential for optoelectronics but face stability challenges. This study demonstrates that vacuum thermal evaporation, a standard technique for depositing overlayers like charge transport layers (CTLs) and metal electrodes during device fabrication, induces a detrimental degradation mechanism in the underlying perovskite film. Photoluminescence (PL) lifetime measurements show consistent degradation for various perovskite compositions subjected to thermal evaporation. X-ray photoelectron spectroscopy (XPS) analysis identifies irreversible chemical changes at the perovskite surface, including iodide loss and altered bonding environments. We show that incidental thermal radiation and the high-vacuum conditions inherent to thermal evaporation are the major factors inducing the degradation. This process-induced damage negatively impacts device-relevant properties, demonstrated by a higher amplified spontaneous emission (ASE) threshold in full diode structures with thermally evaporated CTLs compared to those with a solution-processed CTL. These findings highlight the critical impact of manufacturing process selection on perovskite stability and performance, necessitating careful evaluation of process compatibility for developing robust devices.

Non-Markovian spontaneous emission in a tunable cavity formed by atomic mirrors

Revolutionary perovskite single-crystal thin films offer exceptional potential in optoelectronic and electronic applications due to their unique structural properties and tunable bandgap. Instability, intricate fabrication, and high costs pose significant barriers to their practical application in devices such as solar cells, light-emitting diodes (LEDs), and sensors. Here, we present a "tube in the furnace" chemical vapor deposition (TIF-CVD) method to efficiently fabricate high-quality, stable, and uniform perovskite single-crystal thin films, offering a promising solution to overcome these limitations and paving the way for their integration into next-generation optoelectronic devices. With ultralow trap density (4.35 × 109 cm-3) and higher crystallinity, our method achieves an ultralow threshold of amplified spontaneous emission (ASE) and an exceedingly high gain coefficient (g ∼ 3612.29 cm-1), which represents one of the highest values reported in halide lead perovskite thin films. We further explore the polarization-sensitive photoluminescence (PL), absorption, and photoresponsivity of the thin films, demonstrating their unique optoelectronic behavior under varying polarization states. Our scalable, simple, and cost-effective process for producing single-crystal thin films has potential for next-generation optoelectronic devices, including perovskite lasers, LEDs, and photodetectors (PDs), with a large cavity, enabling larger-scale crystal growth for practical and widespread use.

Studying the luminescent properties and the light amplification capabilities are fundamental investigations for newly synthesized organic compounds intended to act as chromophores. These studies are conducted for compounds in the form of solutions, solids, and also molecules stabilized with the aid of polymers. One of the methods used to study amplification is the generation of amplified spontaneous emission (ASE) using stripe-shaped light beam excitation. This process can lead to the generation of ASE, but also, with the coexistence of microcrystals and scatterers, to the generation of laser action with random feedback, known as random lasing (RL). However, when the degree of light scattering is too high, it can lead to the inhibition of laser emission. Therefore, as an alternative in studying amplification properties, we developed a protocol that allows the investigation of laser action generation using rapidly prototyped polymer waveguides with an embedded dye. The setup used was based on Direct Laser Writing (DLW), which enables the controlled fabrication of multimode optical waveguides. We demonstrated that the use of this technique will allow for the study of the performance of dyes from strictly structured resonators, enabling measurements of gain and lasing threshold. This allowed us to lower the lasing thresholds while maintaining the directionality of emission.

The sixth generation of mobile networks (6G) presents increasing complexity that challenges traditional analysis and performance evaluation methods, necessitating more structured approaches for both research and educational purposes. This study introduces a layered methodology that classifies physical layer impairments, such as amplified spontaneous emission (ASE) noise and fiber nonlinearities into sequential layers. The approach enables independent assessment of individual impairment contributions to overall system performance, facilitating more accurate evaluation of signal quality metrics, including signal-to-noise-ratio (SNR) and optical signal-to-noise-plus-interference ratio (OSNIR) across multiple spectral bands. By implementing this step-by-step analysis framework, researchers can better understand the cumulative impact of various transmission effects, while students can gain progressive insight into complex optical communication principles, making this approach serve dual purposes as both an effective research tool for system optimization and a pedagogical instrument that enhances engineering education. The effectiveness of the methodology is demonstrated through the performance evaluation of a system employing five spectral bands (E, S1, S2, C, and L) under various operating conditions.

We report a cryogenic, cavityless, gain-switched broadband ns-pulsed amplified spontaneous emission (ASE) source in a short single-mode silica thulium-doped fiber (TDF) cooled by liquid nitrogen (LN2). Under the pump of a 1.55-μm ns-pulsed fiber laser with a maximum average power of 687 mW, broadband ASE spans 1750-2475 nm (20-dB bandwidth) with 140-mW average output power and 0.6 mW/nm spectral density at 2.3 μm. The broadband ASE originates from cooperative transitions at 1.9 μm and 2.3 μm and cavityless configuration. The filtered 2.3-μm output shows significantly enhanced slope efficiency of 30% at 77 K, due to the suppression of high-phonon-energy-assisted non-radiative quenching processes on 3H4 level.