Emission Mode Research Articles

Random lasers with controlled emission modes by colloidal semiconductor quantum dots coupled to plasmonic nanorod arrays

Random lasers based on scattering for light amplification have gained extensive attention due to their simple structures. Colloidal semiconductor quantum dots (CSQDs) are excellent candidates as active media for random lasing. However, achieving CSQDs-based random lasers is challenging because the non-radiative Auger recombination produces a remarkable carrier loss. Here, we report random lasers with low thresholds based on the CSQDs coupled to the plasmonic nanorod arrays. The random lasers result from the enhancing excitation and emission rates of the CSQDs through plasmon resonance energy transfer induced by the spectral overlap between the resonant cavity modes of the plasmonic nanorod arrays and the excitons of the CSQDs, which reduces the carrier loss and establishes the optical gain in the CSQDs. Moreover, the incoherent and coherent emission modes can be controlled by varying the filling configurations (i.e., full-filling and partial-filling) of the plasmonic nanorods embedded in anodic aluminum oxide templates. Consequently, the incoherent random laser with a threshold of 19.3 μJ/mm2 and coherent random lasers with a threshold of 13.5 μJ/mm2 are performed, respectively. The proposed system provides a feasible method for low-threshold CSQDs-based random lasers with controlled emission modes, showing a promising avenue for potential applications.

Mechanoluminescence from CaCl2:Eu2+

Mechanoluminescent materials have recently attracted considerable attention as they can convert stimulation of mechanical force into photons that can be used in many areas, ranging from basic energy-saving lighting and display to advanced ultrasound-induced biomedical imaging. However, functional and optical materials that feature emission of mechanoluminescence (ML) have only a limited diversity. Here Eu2+-doped CaCl2 was introduced to expand the family of mechanoluminescent materials. It was demonstrated that CaCl2:Eu2+ could emit photoluminescence, radioluminescence, ML, and persistent luminescence (PersL). Eu2+ ions always acted as luminescent centers (5d→4f transition) during these four emission modes. Moreover, the property of traps of CaCl2:Eu2+ was investigated in detail. Experimental results indicated that there was a competitive relation between ML and PersL, and ML belonged to trap-controlled ML.

The Impact of the Gain Medium Properties and the Resonator Morphology on the Whispering Gallery Mode Spectrum of Polystyrene Microspheres Coated with AgInS2/ZnS Quantum Dots

The modulation of fluorophore emission by whispering gallery modes (WGMs) in active spherical resonators holds great potential for advanced photonic devices. In the present work, we fabricate and systematically study a series of active WGM resonators based on polystyrene microspheres and heavy metal-free ternary AgInS2/ZnS quantum dots with broad and tunable photoluminescence bands coated on their surface as a gain medium. The variation in the mean size and emission wavelength of the quantum dots allowed us to establish a correlation between their characteristics and the WGM properties, including the resonance peaks intensity profile and the Q-factors. Other aspects such as coupling efficiency, polarization-dependent mode damping, and peak broadening are also discussed. Furthermore, we applied statistical analysis on multiple individual resonators within the batch to calculate the standard deviation of the resonator size and ellipticity. Our study highlights that both the cavity and the gain medium influence the WGM parameters in active spherical resonators.

All-Solid-State Infrared Electrochromic Devices Based on Thin Metal Films.

Infrared electrochromic devices (IR-ECDs) are pivotal for dynamic thermal regulation. However, the quest for all-solid-state IR-ECDs with high stability and a broadly tunable range of emissivity remains a challenge. This study presents the development of an all-solid-state infrared electrochromic device (IR-ECD) with the structure of ITO/HxWO3/Ta2O5/Pd/Mg3Ni based on the hydrogen-induced metal-insulator transition of Mg-Ni alloy films. The emissivity modulation is improved by film stack optimization, with changes of 0.32 and 0.47 in the 3-5 and 7.5-14 μm bands, respectively. The introduction of an ultrathin Ti isolation layer between the catalytic and electrolyte layers enhances the cyclic stability. Our findings offer a novel strategy for the design and fabrication of all-solid-state IR electrochromic devices and highlight the potential of Mg-Ni alloy-based all-solid-state IR-ECDs in advanced energy and information fields.

Structural, optical analysis, stress-strain, and dielectric properties of selenium oxide/LaFeO3/blend nanocomposites with tunable properties for optoelectronics and micro-supercapacitors

This work focuses on developing flexible nanocomposites by introducing two types of ceramic nanofillers into a biopolymeric blend for optoelectronic and energy-storing applications. Selenium oxide (SeO2) nanoparticles (NPs) and LaFeO3 NPs were prepared by hydrothermal and solid-state reactions, respectively, and incorporated into the polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) through the solution casting process. Transmission electron microscope and X-ray diffraction tests revealed the creation of hexagonal SeO2 and orthorhombic LaFeO3 NPs, with average sizes of 17 and 93 nm. The blend's degree of crystallinity was dependent on SeO2 NPs and LaFeO3 contents. The infrared absorption spectra revealed the interactions/complexation of the fillers with the blend reactive groups. The scan e-microscope (field emission mode) investigated the films' surface morphology and detected the elements they contain. LaFeO3/SeO2 content impacted stress-strain behavior, raised the tensile strength from 64 to 70.9 MPa, and dramatically lowered the strain at break and toughness. UV–vis-NIR measurements exhibited that the transmittance, extinction coefficient, and refractive index can be tuned by SeO2 and LaFeO3/SeO2 content. The direct (Eg.d)/indirect (Eg.id) band gaps were reduced from 5.25/4.9 eV to 4.95/4.7 eV. The dielectric parameters (constant, loss, energy density, and conductivity) were significantly increased after loading 5.0 wt% LaFeO3/SeO2. The dielectric moduli and Cole-Cole plots were also investigated. The structural modifications and enhancement of the optical features and dielectric parameters make the resulted samples the best candidates for optoelectronic devices and energy-storing applications such as sensors and supercapacitors.

Comparison of TJ and ITO GaN VCSELs in terms of their frequency characteristics

The work focuses on vertical cavity surface emitting lasers (VCSELs) made of nitride materials that emit a wavelength of 445 nm. Two structures were examined: a laser with a tunnel junction and implantation (TJ VCSEL) and an ITO contact (ITO VCSEL). The analysis delves into capacitance phenomena influencing the modulation speed of these lasers. The results highlight differences in active currents between two structures, i.e., currents which contribute to the modulation of the laser emission. According to the authors’ simulations, the TJ VCSEL is more effective in modulating the number of carriers in the active region than the ITO VCSEL, assuming the same modulation amplitude of driving current.

Single-shot measurement of a laser waveform using plasma fluorescence in ambient air

The temporal characterization of a laser pulse is an important task in studying ultrafast laser-matter interactions. It is ideal to measure the temporal profile of the laser pulse with a single laser shot when the repetition rate is low or its interaction with matter is unstable. Here we report a new approach for the single-shot temporal characterization of a laser pulse, based on the TIPTOE (tunneling ionization with a perturbation of the time-domain observation of an electric field) method. The waveform of the laser pulse is reconstructed from the intensity modulation of plasma fluorescence emission. The result of the single-shot measurement is compared with the time-delay scanning TIPTOE measurements, supporting the validity of the single-shot measurement.

An emission-state-switching radio transient with a 54-minute period

Long-period radio transients are an emerging class of extreme astrophysical events of which only three are known. These objects emit highly polarized, coherent pulses of typically a few tens of seconds duration, and minutes to approximately hour-long periods. Although magnetic white dwarfs and magnetars, either isolated or in binary systems, have been invoked to explain these objects, a consensus has not emerged. Here we report on the discovery of ASKAP J193505.1+214841.0 (henceforth ASKAP J1935+2148) with a period of 53.8 minutes showing 3 distinct emission states—a bright pulse state with highly linearly polarized pulses with widths of 10–50 seconds; a weak pulse state that is about 26 times fainter than the bright state with highly circularly polarized pulses of widths of approximately 370 milliseconds; and a quiescent or quenched state with no pulses. The first two states have been observed to progressively evolve over the course of 8 months with the quenched state interspersed between them suggesting physical changes in the region producing the emission. A constraint on the radius of the source for the observed period rules out an isolated magnetic white-dwarf origin. Unlike other long-period sources, ASKAP 1935+2148 shows marked variations in emission modes reminiscent of neutron stars. However, its radio properties challenge our current understanding of neutron-star emission and evolution.

Flexible composite film utilizing VO2 self-adaptive photothermal and infrared radiative cooling for continuous energy harvesting

Self-adaptive photothermal (PT) and radiative cooling (RC) based on insulation-metal phase transition vanadium dioxide (VO2) are among the most promising continuous energy harvesting technologies recently. However, previous work relies on rigid substrates that cannot fit complex or non-planar surfaces. Here, we propose a flexible composite film by bonding a VO2 thin film and a polyimide (PI) substrate with polymethyl methacrylate (PMMA), which achieves efficient spectrally self-adaptive broadband absorption/emission and can convert between the daytime PT mode and nighttime RC mode. Because of the inherent absorption of VO2 and the intricate interplay within multi-layer structure, the solar absorptance of the film could to up to 0.886 in the PT mode with the incorporation of an Al2O3 anti-reflection layer. On the other hand, due to the phase change properties of VO2, this film exhibits a broadband infrared emissivity modulation from 0.32 to 0.82 and reaches a maximum RC power of approximately 244.59 W/m2 in the RC mode at night. Moreover, the film maintains the infrared spectrum switching capability and high emissivity in RC mode even after 104 bending cycles. Our work shows potential to broaden the applications of VO2 smart coatings, including tunable selective emitters, thermal management of spacecraft and smart skins.

Acoustics and Hydrodynamics of the Drop Impact: Two Modes of Sound Packet Emission

Acoustics and Hydrodynamics of the Drop Impact: Two Modes of Sound Packet Emission

Adaptive fabric with emissivity regulation for thermal management of humans

Abstract The heat generation of the human body dramatically varies between resting and active status, so dynamic heat dissipation is required to ensure optimal thermal comfort. Herein, we propose a spectrally self-adaptive smart fabric (SSSF) by covering polyester fabric with silver nanowires, which autonomously adjusts its emissivity in response to the body’s movement status from dry to wet states. During periods of inactivity, the SSSF maintains radiative heat insulation with a low emissivity state of 0.39. Conversely, during vigorous physical activity, its emissivity is improved to 0.83 when the sweat penetrates the SSSF, facilitating greater heat dissipation. Comparative experiments demonstrate the superior thermal management capabilities of the SSSF, with a 19.5 % reduction in heat dissipation power relative to traditional fabrics when in the low emissivity mode, and an impressive 67.6 % enhancement in heat dissipation power as it changes from low to high emissivity mode. This work provides an adaptive approach to emissivity modulation, offering an effective solution for dynamic heat dissipation of humans across various states of activity, thereby enhancing personal thermal comfort.

Generation and Registration of High Harmonics at Surface Plasma in Coherent Wake Emission and Relativistic Oscillating Mirror Modes by High-Power Laser Pulses

Generation and Registration of High Harmonics at Surface Plasma in Coherent Wake Emission and Relativistic Oscillating Mirror Modes by High-Power Laser Pulses

High-cadence monitoring of the emission properties of magnetar XTE J1810−197 with the Stockert radio telescope

Context. Since the detection of a burst resembling a fast radio burst (FRB) from the Galactic magnetar SGR 1935+2154, magnetars have joined the set of favourable candidates for FRB progenitors. However, the emission mechanism of magnetars remains poorly understood. Aims. Observations of magnetars with a high cadence over extended timescales have allowed for their emission properties to be determined, in particular, their temporal variations. In this work, we present the results of the long-term monitoring campaign of the magnetar XTE J1810−197 since its second observed active phase from December 2018 until November 2021, with the Stockert 25 m radio telescope. Methods. We present a single pulse search method, improving on commonly used neural network classifiers thanks to the filtering of radio frequency interference based on its spectral variance and the magnetar’s rotation. Results. With this approach, we were able to lower the signal to noise ratio (S/N) detection threshold from 8 to 5. This allowed us to find over 115 000 spiky single pulses – compared to 56 000 from the neutral network approach. Here, we present the temporal variation of the overall profile and single pulses. Two distinct phases of different single pulse activity can be identified: phase 1 from December 2018 to mid-2019, with a few single pulses per hour, and phase 2 from September 2020 with hundreds of single pulses per hour (with a comparable average flux density). We find that the single pulse properties and folded profile in phase 2 exhibit a change around mid-March 2021. Before this date, the folded profile consists of a single peak and single pulses, with fluences of up to 1000 Jyms and a single-peaked width distribution at around 10 ms. After mid-March 2021, the profile consists of a two peaks and the single pulse population shows a bimodal width distribution with a second peak at 1 ms and fluences of up to 500 Jyms. We also present asymmetries in the phase-resolved single pulse width distributions beginning to appear in 2020, where the pulses arriving earlier in the rotational phase appear wider than those appearing later. This asymmetry persists despite the temporal evolution of the other single pulse and emission properties. Conclusions. We argue that a drift in the emission region in the magnetosphere may explain this observed behaviour. Additionally, we find that the fluence of the detected single pulses depends on the rotational phase and the highest fluence is found in the centre of the peaks in the profile. While the majority of the emission can be linked to the detected single pulses, we cannot exclude another weak mode of emission. In contrast to the pulses from SGR 1935+2154, we have not found any spectral feature or bursts with energies in the order of magnitude of an FRB during our observational campaign. Therefore, the question of whether this magnetar is capable of emitting such highly energetic bursts remains open.

Thermal Emission Modulation by Electron Population in Quantum Dots

Thermal Emission Modulation by Electron Population in Quantum Dots

Tunable multicolor-emission in Eu3+ and Tb3+ codoped Cs2NaInCl6:Sb3+ double perovskite nanocrystals and its dual-model anti-counterfeiting and temperature-sensing applications

Lead-free metal halide double perovskites with non-toxicity and stable self-trapped excitons (STEs) have received considerable attention in the field of photoelectric applications. However, it is difficult to achieve independent control of its photoluminescence performance to meet the requirements of multi-band emission. Herein, a doping strategy was employed to introduce lanthanide ions (Ln3+) into Cs2NaInCl6:Sb3+ nanocrystals (NCs), enabling the multicolor emission modulation ranging from blue to red and even white light. Benefiting from the efficient energy transfer from Sb-related self-trapped excitons to Ln3+ ions, green and red emissions originate from the 5D0→7FJ (J = 1, 2, 3, 4) transition of Eu3+ ions and 5D4-7FJ (J = 6, 5, 4, 3) transition of Tb3+ ions, respectively. According to the tunable polychromatic photoluminescence characteristics of doped NCs, the dual-mode fluorescent anti-counterfeiting applications were exhibited. Furthermore, the distinct temperature sensitivities exhibited by blue (453 nm) and red (617 nm) emission in Cs2NaInCl6:Sb3+/Eu3+ NCs provide the opportunity for the optical thermometry, which demonstrates the maximum absolute and relative sensitivity are 0.0018 and 0.43 % K−1, respectively. These results indicate that the synthesized codoped NCs have the potential applications in multifunctional fields, such as optical thermometer, fluorescence anti-counterfeiting, and multicolor-LEDs.

Novel CeF3:Tm3+, Er3+ nanoparticles: NIR up-down conversion luminescence properties based on energy transfer of Tm3+ and Ce3+

A novel CeF3:Tm3+, Er3+ NIR up-down conversion luminescent nanoparticles with highly efficient visible and near-infrared second window (NIR-II) emission were synthesized by direct precipitation and hydrothermal methods. The two different emission modes of visible-NIR II light of Er3+were realized through the energy transfer of Tm3+ and Ce3+at the excitation wavelength of 808 nm. Which successfully combined the narrow emission peaks of visible light and the deep tissue penetration advantage of NIR-II. First, the effects of preparation conditions on the structure, morphology, stability and luminescence properties of CeF3:Tm3+, Er3+ nanoparticles were analyzed by XRD, SEM, TEM and PL. The results showed that the crystallinity, morphology and luminescence intensity of CeF3:Tm3+,Er3+ nanoparticles produced by hydrothermal method (reaction time of 10 h) were optimal compared with that of direct precipitation method. CeF3: Tm3+,Er3+ nanoparticles has better thermal stability, and fluorescence lifetime of 5D0→7F2 (525 nm), 4I15/2→4I11/2 (1066 nm) and 4I15/2→4I13/2 (1386 nm) for Er3+ are 15.51 ns, 48.78 us and 57.06 us, separately. At the same time, the surface of CeF3:Tm3+, Er3+ nanoparticles was modified by PEG and Lys. And then the effects of the surface modification on the hydration size, zeta potential and up-down conversion luminescent properties (visible and NIR-II light emission) were investigated. The results show that the modification of PEG effectively slows down the agglomeration of CeF3:Tm3+, Er3+ nanoparticles and improves their stability and dispersion under the same conditions. More importantly, the modification of PEG effectively increases the up-conversion luminescence intensity of CeF3:Tm3+, Er3+ nanoparticles under 808 nm excitation. Moreover, the CeF3:Tm3+, Er3+-PEG nanoparticles with 20–40 nm showed stronger NIR up-down conversion emission intensity in aqueous solutions (pH = 5,6,7) and better thermal stability. Furthermore, the CeF3:Tm3+, Er3+-PEG nanoparticles has low cytotoxicity and good biocompatibility. This study provides a theoretical basis for the development of high-performance rare-earth NIR up-down conversion luminescence materials.

Observation of Extraneous Axial Cavity Modes of a Single-Mode Solid-State Laser Using Ultrahigh-Contrast Fabry–Perot Interferometry

Extraneous axial optical cavity modes produced by a single-mode frequency-doubled neodymium-doped yttrium orthovanadate (Nd:YVO[Formula: see text]) laser were observed in spectra obtained via ultrahigh-contrast Fabry–Perot interferometry. These modes, which are much weaker than the primary axial mode emission, are separated by [Formula: see text] GHz and display decreasing intensity with increasing shift from the primary laser line and with increasing laser output power. The possible presence of such modes in target sample spectra necessitates that caution be used in the interpretation of spectral peaks in laser spectroscopy studies, particularly Brillouin light scattering experiments. This work also showcases the remarkable capabilities of modern multipass Fabry–Perot interferometry in the detection of exceedingly weak optical signals shifted in frequency by only a few gigahertz from the primary laser emission line.

Large-Area Near-Infrared Emission Enhancement on Single Upconversion Nanoparticles by Metal Nanohole Array.

Single lanthanide (Ln) ion doped upconversion nanoparticles (UCNPs) exhibit great potential for biomolecule sensing and counting. Plasmonic structures can improve the emission efficiency of single UCNPs by modulating the energy transferring process. Yet, achieving robust and large-area single UCNP emission modulation remains a challenge, which obstructs investigation and application of single UCNPs. Here, we present a strategy using metal nanohole arrays (NHAs) to achieve energy-transfer modulation on single UCNPs simultaneously within large-area plasmonic structures. By coupling surface plasmon polaritons (SPPs) with higher-intermediate state (1D2 → 3F3, 1D2 → 3H4) transitions, we achieved a remarkable up to 10-fold enhancement in 800 nm emission, surpassing the conventional approach of coupling SPPs with an intermediate ground state (3H4 → 3H6). We numerically simulate the electrical field distribution and reveal that luminescent enhancement is robust and insensitive to the exact location of particles. It is anticipated that the strategy provides a platform for widely exploring applications in single-particle quantitative biosensing.

The phenomenon of skin contraction in CO2 LASER surgical incisions using superpulse and continuous emission mode - preliminary study.

The skin contraction phenomenon occurs due to the energy emitted by the surgical CO2 LASER affecting the collagen architecture and intracellular water content in tissues. The study aimed to assess how gender, age, breed, body-weight, CO2 LASER emission mode, and potency influence skin contraction following the incision. The study involved 80 dogs (N = 80) of both genders, multiple breeds, undergoing major surgery with CO2 LASER. Subjects were grouped based on LASER potency (12 or 15 Watts) and emission mode (Superpulse-SP or Continuous-CT): GSP12, GSP15, GCT12, and GCT15. A 10mm incision was performed using the surgical CO2 LASER beam, consistently employing a focal point of 0.4mm, positioned at a distance of 1mm from the skin surface, and always maintained perpendicular to it, and resulting lengths measured with a digital caliper. Results were considered significant for p-value < 0.05. GSP12 showed minimal contraction, while GCT15 exhibited the most significant. Male subjects in GCT12, GCT15, and GSP12 experienced less contraction than females. Purebred dogs had greater contraction than mixed breeds. GSP12 individuals showed age-related contraction decrease (p < 0.01), with skin contracting by 0.09mm per year. Weight and skin contraction trended towards significance (p = 0.06), with a 0.02mm increase per unit weight. For a constant power of 12 W, the analysis of the relationship between the emission mode of the LASER beam and the final skin contraction (GSP12 vs. GCT12) revealed statistically significant differences (p < 0.01). This study suggests that the use of the Continuous mode of LASER emission, regardless of the power used, is associated with a higher level of final skin contraction. TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION FOR PROSPECTIVELY REGISTERED TRIALS: Project approval registration number by the Research and Teaching Ethics Committee (CEIE),Faculty of Veterinary Medicine-University of Lisbon (FMV_ULisboa), Lisboa-Portugal, N/Refª 015/2022.

Stimuli-induced modulation of white light emission in colloidal polymer particles: Design of chemosensors and dynamic chromism toward unclonable patterning and its classification based on machine learning

Stimuli-responsive light-emitting materials have gained significant attention due to their potential applications in optoelectronic devices, chemosensors, anticounterfeiting inks, and unclonable encryption. Coumarin-containing fluorescent polymer particles with light-, pH-, and thermo-responsiveness were prepared by distillation-precipitation polymerization of hydroxyethyl methacrylate and 2-(dimethylamino)ethyl methacrylate. White light emission was observed by physical incorporation of hydroxyl-functionalized spiropyran (SPOH) into the colloidal polymer particles in a certain ratio of the colloidal polymer particles and SPOH content. The white light emission was obtained by modulating pH and temperature to finely tune the Förster resonance energy transfer process and cover the entire visible spectra from the emissive lights. This phenomenon was successfully used to prepare pH sensors, dynamic anticounterfeiting inks, unclonable patterning, and also white light-emitting colloids, films, coatings, and diodes. As an example, a white light-emitting diode was fabricated using the SPOH-doped colloidal polymer particles in poly(vinyl alcohol) matrix having Commission Internationale del'Eclairage color coordinates of (0.31, 0.33). Dynamic chromism and preparation of randomly distributed blue, red, and white light-emitting patterns are examples of advanced anticounterfeiting and encryption methods that were generated via the prepared low-cost environmentally friendly waterborne ink. For the authentication purpose of the unclonable patterns, the classification algorithms were designed based on machine learning to classify the true patterns from the false ones.