Wide Emission Research Articles

An ultrawide-range photochromic molecular fluorescence emitter

Photocontrollable luminescent molecular switches capable of changing emitting color have been regarded as the ideal integration between intelligent and luminescent materials. A remaining challenge is to combine good luminescence properties with wide range of wavelength transformation, especially when confined in a single molecular system that forms well-defined nanostructures. Here, we report a π-expanded photochromic molecular photoswitch, which allows for the comprehensive achievements including wide emission wavelength variation (240 nm wide, 400–640 nm), high photoisomerization extent (95%), and pure emission color (<100 nm of full width at half maximum). We take the advantageous mechanism of modulating self-assembly and intramolecular charge transfer in the synthesis and construction, and further realize the full color emission by simple photocontrol. Based on this, both photoactivated anti-counterfeiting function and self-erasing photowriting films are achieved of fluorescence. This work will provide insight into the design of intelligent optical materials.

Tackling toxicity and stability using eco-friendly metal-halide ion substituted perovskite nanocrystals for advanced display color conversion

In recent years organic–inorganic hybrid halide perovskites nanocrystals have made a remarkable impact in display color converting layer application. However, lead toxicity and stability issues always pose arduous challenges. In this regard, the incorporation of a suitable metal ion to reduce toxicity and enhance stability is a widely tested method. In this study, we used a simple ligand-assisted reprecipitation (LARP) technique to simultaneously introduce metal ion and halide ion substitution by synthesizing MAPb1-xZnxBr3-2xCl2x nanocrystals (NCs). Being eco-friendly with a smaller ionic radius than lead ion, zinc metal ion was chosen as a substitute. With the variation of Zn2+ concentration, the highest quantum yield of 95 % was recorded with an emission width of 21 nm. Temperature-dependent photoluminescence (PL) studies revealed the higher optical phonon-exciton interaction after Zn2+ incorporation leading to radiative transition in NCs. Variation of PL peak energy with temperature revealed the reduced thermal chromaticity of Zn2+ incorporated NCs making them suitable for display application. Further, these NCs maintained a stable cubic structure and luminescence up to 150 °C, indicating higher thermal stability. The MAPb0.9Zn0.1Br2.8Cl0.2 (x = 0.1 or 10 mol%) NCs embedded in PMMA (poly (methyl methacrylate) polymer matrix coated LED emits narrow width, green light with color coordinate (0.15, 0.79), which is closer to green coordinate (0.17, 0.79) in Rec.2020. This helps to reproduce close to 97 % color gamut of Rec.2020. This research paves the way for finding less toxic and stable green light-emitting materials instead of cadmium-based molecules.

Wide Range Controllable Direction Single Emission Peak Microstructured Lasers Array

Wide Range Controllable Direction Single Emission Peak Microstructured Lasers Array

Substituted Pyrrole‐based Schiff Bases: Effect On The Luminescence Of Neutral Heteroleptic Cu(I) Complexes

AbstractNeutral Cu(I) complexes containing Schiff bases as chelating N‐donors and phosphines as P‐donors were efficiently isolated and characterized. The imines were obtained by straightforward condensation between pyrrole‐2‐carboxaldehyde and the corresponding aromatic amines. The structure of most of the Cu(I) species was elucidated through single‐crystal X‐ray diffraction. The Cu(I) complexes exhibited intense absorptions around 400–500 nm ascribed to MLCT transitions. For some Cu(I) derivatives, orange‐ and red‐orange emissions were detected upon excitation with near‐UV and blue irradiation in the solid state. The emission maxima were red‐shifted once the benzothiazole‐derived Schiff base or Xantphos were employed as chelating ligands. Microsecond‐long lifetimes, wide emissions, and large Stokes shifts suggest the involvement of triplet states in the luminescent process. Electrochemical measurements and DFT calculations were employed to rationalize the photoluminescence properties, which were ascribed to mixed 3LC/3MLCT transitions.

The role of co-dopant Ce3+ on the spectral properties of Dy3+ activated YAG single crystal for yellow green laser application

Ce3+ and Dy3+ co-doped Y3Al5O12 (abbr. as Ce, Dy: YAG) single crystal was grown by the Czochralski method. As compared with the absorption spectrum of Dy: YAG crystal, the synchronous doping of Ce3+ ions into Dy: YAG crystal resulted in a wide excitation band in the 425–500 nm region peaking around 447 nm owing to the 4f→5d transition of Ce3+ ions, and inhomogeneous broadening absorption with the full width at half maximum (FWHM) from 4 nm to 39 nm. Furthermore, due to the efficient energy transfer from Ce3+ to Dy3+ ions in YAG crystal, under 447 nm excitation Ce, Dy: YAG crystal showed intense and wide characteristic yellow green emission, whose intensity increased by 12.3 times and FWHM from 12 nm to 113 nm as compared with Dy: YAG crystal. The fluorescence lifetime of Dy3+: 4F9/2 level has increased from 693.1 μs to 2.062 ms. Based on the above results, Ce, Dy: YAG crystal would be an excellent candidate for the realization of yellow green waveband laser output.

Hybrid methodology development for lubrication regimes identification based on measurements, simulation, and data clustering

The lubrication regimes of a laboratory scale journal bearing were analysed with wide band acoustic emission (AE) measurements. The analysis was supported by data-based clustering of AE data. Digital twin of the journal bearing was generated with Simpack multi-body simulation software to study opportunities for developing a hybrid methodology for more complex systems monitoring. The AE and data-based clustering approach can be effectively used to reveal fundamental lubrication modes, i.e., hydrodynamic (HL), mixed (ML) and boundary (BL) lubrication as a function of Hersey number, which can be evaluated in situ by utilizing digital twin. Besides AE the other parameters monitored were friction torque, bearing temperature, loading, sliding velocity and oil pressure. The materials used in the experiments were case-hardened 18CrNiMo7–6 steel and nitrided 42CrMo7 steel. The tests were lubricated with synthetic extreme-pressure gear oil (SGN 320) and the bearing temperature was kept constant during the tests. The bearing loading and sliding velocity during tests were varied in the wide range resulting in different lubrication situations. The acoustic emission signals power and frequency content was analysed, and essential features were extracted for data clustering. For lubrication regime change identification the parameters such as signal RMS and coefficient of variation (CV) proved to be important, while signal kurtosis showed to be the most sensitive in discovering anomalies. The high sensitivity requires data filtering to remove erroneous peaks and to reveal real trends more clearly. It is also interesting to notice the changes in AE frequency during changing to different lubrication regime. In literature different clustering and classification methods has been proposed and applied for journal bearing status identification. Here the selected unsupervised clustering method was the mean-shift clustering due to fact, that the lubrication regimes in the Stribeck curve form an inseparable continuum. The algorithm does not require specifying the number of clusters in advance, i.e., the clusters are determined by the algorithm with respect to the data. The results were compared to simulations with digital twin. i.e., by comparing simulated digital twin film thickness and measured AE kurtosis relative to measured Hersey number. It was concluded that digital twins can be utilized as virtual sensor for in situ detecting of lubrication regimes, if it is possible to calibrate the simulation with sensitive measurements, e.g., AE. It is obvious that simulations alone cannot predict suddenly appearing anomalies, such as impurities or surface fatigue failures.

A sequence of Type Ib, IIb, II-L, and II-P supernovae from binary-star progenitors with varying initial separations

Over the last decade, evidence has accumulated that massive stars do not typically evolve in isolation but instead follow a tumultuous journey with a companion star on their way to core collapse. While Roche-lobe overflow appears instrumental for the production of a large fraction of Type Ib and Ic supernovae (SNe), variations in the initial orbital period, $P_ init $, of massive interacting binaries may also produce a wide diversity of case B, BC, or C systems, with pre-SN stars endowed from minute to massive H-rich envelopes. Focusing here on the explosion of the primary donor star, originally 12.6\ we used radiation hydrodynamics and nonlocal thermodynamic equilibrium time-dependent radiative transfer to document the gas and radiation properties of such SNe, covering Types Ib, IIb, II-L, and II-P. Variations in init $ are the root cause of the wide diversity of our SN light curves, which present single-peak, double-peak, fast-declining, or plateau-like morphologies in the $V$ band. The different ejecta structures, expansion rates, and relative abundances (e.g., H, He, and can lead to a great deal of diversity in terms of spectral line shapes (absorption versus emission strength and width) and evolution. We emphasize that Halpha is a key tracer of these modulations, and that He is an enduring optical diagnostic for the presence of He. Our grid of simulations fares well against representative Type Ib, IIb, and II-P SNe, but interaction with circumstellar material, which is ignored in this work, is likely at the origin of the tension between our Type II-L SN models and observations (e.g., of SN\,2006Y). Remaining discrepancies in the rise time to bolometric maximum of our models call for a proper account of both small-scale and large-scale structures in core-collapse SN ejecta. Discrepant Type II-P SN models, with a high plateau brightness but small spectral line widths, can be fixed by adopting more compact red-supergiant star progenitors.

Luminescent manifestations of ytterbium ions in the crystal structure of silicate apatite

The manifestation of ytterbium ions in the microcrystals of the Sr2Y6.8YbSi6O26:Er0.2 solid solution with apatite structure was studied on the basis of low-temperature photoluminescence (PL) spectroscopy and spectral-kinetic measurement data. Intracenter down-conversion luminescence of Er3+ ions in the visible and IR ranges was detected. Up-conversion luminescence of Er3+ ions is observed upon IR excitation due to excitation of Yb3+ ions and subsequent energy transfer Yb3+ → Er3+. Overlapping bands at 412 and 430 nm with a Stokes shift of less than 0.3 eV are observed in the PL spectra at room temperature. These emission bands are assigned to the spin-allowed and spin-forbidden 4f135d → 4f14 transitions from the low-spin and high-spin exciting states of Yb2+ ion, respectively. The PL decay kinetics for transitions from the low-spin states is characterized by a dominant component τ = 0.39 ns. An alternative model of Yb3+ luminescence center associated with a charge transfer band does not explain the data of low-temperature (5K) PL spectroscopy. At T = 5 K, a new wide emission band with a maximum at 696 nm and a Stokes shift of 1.1 eV appears in the PL spectrum. Two options of this PL band nature are considered. The first is the luminescence of defects having a vacancy nature. The second possible option is the manifestation of anomalous luminescence of Yb2+ ions, which occupy a different crystallographic position in the apatite crystal structure.

Tuning Molecular Packing by Twisting Structure to Facilely Construct Highly Efficient Solid‐State Fluorophores for Two‐Photon Bioimaging and Photodynamic Therapy

AbstractThe traditional design strategy for constructing highly bright solid‐state luminescent materials relies on incorporating aggregation‐induced emission (AIE) scaffolds, molecular rotors, or bulky substituents to prevent close cofacial packing, which limits the strategy diversity in developing new materials. Herein, a strategy of tuning molecular packing by twisting molecular structure of conventional aggregation‐caused quenching fluorophore is proposed to endow materials with AIE effect and enhance the solid‐state fluorescence. Accordingly, a series of 1,4‐bis(diphenylamino)‐2,5‐disubstituted benzene fluorophores exhibiting AIE characteristics, high solid‐state fluorescence efficiency (up to 0.99), wide emission color tunability, and good near‐infrared (NIR) two‐photon absorption is facilely developed. All these luminogens can specifically stain intracellular lipid droplets with a high signal‐to‐noise ratio, high biocompatibility, and good photostability. Besides, the luminogens exhibit effective reactive oxygen species (ROS) generation capability upon low‐power white light irradiation. Among them, the AIE luminogen, named BDBDC, integrating the NIR emission, good NIR two‐photon absorption and strongest ROS generation demonstrates superior performances in two‐photon fluorescence imaging of various tissues and photodynamic cancer therapy. This molecular design philosophy provides a new way of designing highly bright solid‐state fluorophores for practical applications.

The synthesis and properties of Ca3 Sc2 Si3 O12 :Ce3+ (CSSG) phosphor are utilized for the development of human-centric lighting light-emitting diodes (HCL-LEDs).

In this study, cerium ion (Ce3+ )-doped calcium scandium silicate garnet (Ca3 Sc2 Si3 O12 , abbreviated CSSG) phosphors were successfully synthesized using the sol-gel method. The crystal phase, morphology, and photoluminescence properties of the synthesized phosphors were thoroughly investigated. Under excitation by a blue light-emitting diode (LED) chip (450 nm), the CSSG phosphor displayed a wide emission spectrum spanning from green to yellow. Remarkably, the material exhibited exceptional thermal stability, with an emissivity ratio at 150°C to that at 25°C reaching approximately 85%. Additionally, the material showcased impressive optical performance when tested with a blue LED chip, including a color rendering index (CRI) exceeding 90, an R9 value surpassing 50, and a biological impact ratio (M/P) above 0.6. These noteworthy findings underscore the potential applications of CSSG as a white light-converting phosphor, particularly in the realm of human-centered lighting.

Multisite Fine-Tuning in Hybrid Cadmium Halides Enables Wide Range Emissions for Anti-Counterfeiting.

Achieving tunable emissions spanning the spectrum, from blue to near-infrared (NIR) light, within a single component is a formidable challenge with significant implication, particularly in tailoring multicolor luminescence for anti-counterfeiting purposes. In this study, we demonstrate a broad spectrum of emissions, covering blue to red and extending into NIR light in [BPy]2CdX4 : xSb3+ (BPy=Butylpyridinium; X=Cl, Br; x=0 to 0.08) through precise multisite structural fine-tuning. Notably, the multicolor emissions from [BPy]2CdBr4 : Sb3+ manifest a distinctive pattern, transitioning from blue to yellow in tandem with the host [BPy]2CdBr4 and further extending from yellow to NIR with its homologous [BPy]2CdCl4 : Sb3+, resulting in the simultaneous presence of intersecting and independent emission colors. Detailed modulation of chemical composition enables partial luminescence switching, facilitating the creation of diverse patterns with multicolor luminescence by employing [BPy]2CdX4 : xSb3+ as phosphors. This study for the first time successfully implements several groups of tunable emission colors in a single matrix via multisite fine-tuning. Such an effective strategy not only develops the specific relationships between tunable emissions and adjustable compositions, but also introduces a cost-effective and straightforward approach to achieving unique, high-level, plentiful-color and multiple-information-storage labels for advanced anti-counterfeiting applications.

Multisite Fine‐Tuning in Hybrid Cadmium Halides Enables Wide Range Emissions for Anti‐Counterfeiting

AbstractAchieving tunable emissions spanning the spectrum, from blue to near‐infrared (NIR) light, within a single component is a formidable challenge with significant implication, particularly in tailoring multicolor luminescence for anti‐counterfeiting purposes. In this study, we demonstrate a broad spectrum of emissions, covering blue to red and extending into NIR light in [BPy]2CdX4 : xSb3+ (BPy=Butylpyridinium; X=Cl, Br; x=0 to 0.08) through precise multisite structural fine‐tuning. Notably, the multicolor emissions from [BPy]2CdBr4 : Sb3+ manifest a distinctive pattern, transitioning from blue to yellow in tandem with the host [BPy]2CdBr4 and further extending from yellow to NIR with its homologous [BPy]2CdCl4 : Sb3+, resulting in the simultaneous presence of intersecting and independent emission colors. Detailed modulation of chemical composition enables partial luminescence switching, facilitating the creation of diverse patterns with multicolor luminescence by employing [BPy]2CdX4 : xSb3+ as phosphors. This study for the first time successfully implements several groups of tunable emission colors in a single matrix via multisite fine‐tuning. Such an effective strategy not only develops the specific relationships between tunable emissions and adjustable compositions, but also introduces a cost‐effective and straightforward approach to achieving unique, high‐level, plentiful‐color and multiple‐information‐storage labels for advanced anti‐counterfeiting applications.

A Tunable artificial plasmonic nanolaser with wide spectrum emission operating at room temperature

Abstract With information and communication technology developing fast, a key objective in the field of optoelectronic integrated devices is the reduction of nano-laser size and energy consumption. Photonics nanolasers are unable to exceed the diffraction limit and typically exhibit low modulation rates of several GHz. In contrast, plasmonic nanolaser utilize highly confined surface plasmon polariton (SPP) modes that can surpass diffraction limit and their strong Purcell effect can accelerate the modulation rates to several THz. Here, we propose a parametrically tunable artificial plasmonic nanolasers based on Metal-Insulator-Semiconductor-Insulator-Metal (MISIM) structure, which demonstrates the capability to compress the mode field volume to λ/14. As the pump power increases, the proposed artificial plasmonic nanolasers exhibits wide output spectrum of 20nm. Additionally, we investigate the impact of various cavity parameters on the nanolaser’s output threshold, offering potentials for realizing low-threshold artificial plasmonic nanolasers. Moreover, we observe a blue shift in the center wavelength of the nanolaser output with thinner gain layer thickness, predominantly attributed to the increased exciton–photon coupling strength. Our work brings inspiration to several areas, including Spaser-based interconnects, Nano-LEDs, spontaneous emission control, miniaturization of photon condensates, eigenmode engineering of plasmonic nanolasers, and optimal design driven by Artificial Intelligence (AI).

Shear shock wave injury in vivo: High frame-rate ultrasound observation and histological assessment

Using high frame-rate ultrasound and ¡1μm sensitive motion tracking we previously showed that shear waves at the surface of ex vivo and in situ brains develop into shear shock waves deep inside the brain, with destructive local accelerations. However post-mortem tissue cannot develop injuries and has different viscoelastodynamic behavior from in vivo tissue. Here we present the ultrasonic measurement of the high-rate shear shock biomechanics in the in vivo porcine brain, and histological assessment of the resulting axonal pathology. A new biomechanical model of brain injury was developed consisting of a perforated mylar surface attached to the brain and vibrated using an electromechanical shaker. Using a custom sequence with 8 interleaved wide beam emissions, brain imaging and motion tracking were performed at 2900 images/s. Shear shock waves were observed for the first time in vivo wherein the shock acceleration was measured to be 2.6 times larger than the surface acceleration ( 95g vs. 36g). Histopathology showed axonal damage in the impacted side of the brain from the brain surface, accompanied by a local shock-front acceleration of >70g. This shows that axonal injury occurs deep in the brain even though the shear excitation was at the brain surface, and the acceleration measurements support the hypothesis that shear shock waves are responsible for deep traumatic brain injuries.

Dual fluorescence induced thermally activated delayed fluorescence materials based on 2,4-Diphenylthieno[3,2-d]pyrimidine with an efficient single-molecular white electroluminescence

Dual fluorescence compounds exhibit a wide emission spectrum in visible-light range and show huge application prospect in white-light OLED (WOLED). However, few of them can realize the trade-off between high color purity of white-light emission and high emission efficiency. In this work, using sulfur atom-fused electron acceptor (A) unit 2,4-diphenylthieno[3,2-d]pyrimidine (TP) and planar electron donor (D) unit phenothiazine (PTZ), a series of novel dual fluorescence compounds with simple twisting D-A configuration were designed and synthesized, denoted as PTZ-2TP, PTZ-4TP and DPTZ-TP, respectively. Simultaneous dual fluorescence emission could be realized both solution and film state of the current system via optimizing polarization environment and doped concentration, which are attributed to the characteristic quasi-axial (QA) and quasi-equal (QE) conformations. Subsequently, these compounds were successfully applied in WOLED with high efficiency. DPTZ-TP as emitter endows the WOLED with the best device performance with greenish-white light emission, CIE coordinates of (0.33, 0.44) and high EQEmax of 11.87%, which is the highest records of such single compound systems.

Te Cluster Engineering for Tunable Optical Response

AbstractThe construction of active materials with controllable optical response facilitates the development of advanced photonic devices. However, the achievement of robust active materials with wide wavelength tunable and broadband emission remains a great challenge, mainly due to the fixed energy levels of conventional active dopants and limited inhomogeneous broadening in common hosts. Here, the study proposes that the cluster in the mesoscopic scale of ≈1 nm may break this bottleneck issue and demonstrate a strategy for the management of photon emission by engineering the cluster evolution. The amorphous glass as the host to tailor the characteristic configuration of Te clusters from 1 to 2 nm by control of the topological structures in glass is employed. Impressively, it presents a distinct optical response totally different from the conventional active centers and this enables to construct of active photonic glass with continuously tunable emission from 888 to 1064 nm. More importantly, Te cluster‐activated photonic glass fibers are fabricated and the broadband on‐off gain is successfully achieved. Furthermore, benefiting from the unique tunable emission, novel near‐infrared devices are constructed and their application in imaging is demonstrated. The approach of cluster engineering mediated tunable optical response is believed to bring new opportunities for developing advanced photonic devices.

Sub-60-fs mode-locked Tm,Ho:CaYLuAlO4 laser at 2.05 µm

Tm,Ho:CaYLuAlO4 (Tm,Ho:CALYLO) crystal has wide emission spectra both for π-polarization and σ-polarization, showing significant potential for the generation of ultrashort pulses. Here, a widely tunable and passively mode-locked laser operation based on Tm,Ho:CALYLO crystal under two polarizations was demonstrated for what we believe to be the first time ever. For π-polarization, a maximum output power of 1.52 W and a tuning range of 255.3 nm were achieved in the continuous wave (CW) regime. In the mode-locked regime, a pulse duration of 68 fs and an average output power of 228 mW were achieved upon GaSb-based semiconductor saturable absorber mirror (SESAM). As for σ-polarization, a broader tuning range of 267.1 nm was realized, leading to the shorter pulse duration of 58 fs at 79.7 MHz repetition rate.

Ultra-broadband and wide-angle nonreciprocal thermal emitter based on Weyl semimetal metamaterials

Abstract Nonreciprocal thermal radiation can violate Kirchhoff’s law and exhibit different emissivity at symmetric polar angles relative to the normal direction. Realizing a mid-infrared broadband nonreciprocal thermal emitter with a wide emission angle range is a fundamental yet challenging task, particularly without the need for an external magnetic field. Here, we propose a nonreciprocal thermal emitter operating in the mid-infrared that achieves a significantly nonreciprocal thermal radiation in a wavelength range from 12 μm to 20 μm, spanning a wide angular range from 16° to 88°. This is achieved by utilizing a multilayered Weyl semimetal (WSM)/dielectric structure, which takes the advantage of the strong nonreciprocity of WSMs with different Fermi levels and epsilon-near-zero-induced Brewster modes. The results provide a wider angular range in the broad mid-infrared band compared to previous attempts. The robustness of the nonreciprocal radiation is confirmed through wavelength-averaged emissivity across the azimuth angle φ range from 0° to 360°. Some possible materials and nanostructures as dielectric layers are discussed, showcasing the flexibility and reliability of the design. This work holds promising potential applications such as enhanced radiative cooling, thermal emitters for medical sensing and infrared heating, energy conversion, etc.

The first demonstration of wavelength-tunable Yb3+-doped low silica calcium aluminosilicate (LSCAS) glass lasers

We report on the first demonstration of diode-pumped wavelength-tunable Yb3+-doped low silica calcium aluminosilicate (LSCAS) glass lasers. Using a 976 nm diode laser as pump source, a Yb:LSCAS laser has been successfully achieved with a maximum output power of about 0.28 W. Using an MgF2 thin plate as birefringence filter, we have found that the lasing wavelength can be tuned with a range of about 60 nm. We have also analyzed the intracavity round-trip loss of the current laser cavity, and related it to the optical quality of the used Yb glass. This sheds light on the path of the development of upcoming Yb3+ glass lasers in the future since it has many advantages, and after improving the optical quality, the wide and smooth emission spectrum of Yb:LSCAS will be very conducive to obtaining femtosecond pulse lasers.

Broadband Ca3MgZrGe3O12:Cr3+ garnet phosphor for high-performance NIR pc-LED application.

The near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) is heavily reliant upon the performance of NIR phosphors. However, the current NIR pc-LEDs suffer from low photoelectric efficiency and insufficient near-infrared output power. In this study, Cr3+-doped Ca3MgZrGe3O12 phosphors leading to high-performance NIR pc-LEDs were developed for the first time. They feature robust and wide NIR emission that extends over the spectrum from 650 to 1100 nm with a full width at half maximum of 120 nm, a high quantum yield of 82% and excellent thermal stability of T50% = 250 °C and I150 °C = 80% when excited at 460 nm. The NIR pc-LED was constructed by combining the Ca3MgZrGe3O12:0.04Cr3+ phosphor with a blue LED chip, resulting in a device that exhibits a photoelectric conversion efficiency of 20% and a near-infrared output power of 54.19 mW when operated at a current of 100 mA. The obtained luminous efficacy is superior to that of the vast majority of current broadband near-infrared pc-LEDs. In addition, this NIR pc-LED exhibits strong penetration and its applications in bio-imaging are demonstrated. The results indicate that Ca3MgZrGe3O12:Cr3+ NIR broadband phosphors are efficient for NIR pc-LEDs.