Light Emission Spectra Research Articles

Spectrally independent and wide-angle light extraction of organic light emitting diodes with randomly disassembled nanostructure.

Organic Light Emitting Diodes (OLEDs) have emerged as popular screen advancements in digital appliances, thanks to their unique characteristics such as self-emitting ability, transparency, true dark tone, and flexibility. In comparison to liquid crystal displays, OLED displays offer superior performance. Moreover, OLEDs are also a promising option for illuminating purposes. Although significant progress in enhancing the internal quantum efficiency (IQE) of OLEDs, achieving an external quantum efficiency that matches their full potential has proven challenging due to optical losses. This paper explores the utilization of Randomly Disassembled Nanostructures (RaDiNa) for light extraction in flexible OLEDs. The study confirms that the implementation of RaDiNa enhances light extraction efficiency, particularly at angles above the critical angle, leading to an increased external quantum efficiency (EQE). The application of a cured polydimethylsiloxane (PDMS) onto the substrate resulted in the RaDiNa-structured OLEDs demonstrating not only an extended viewing angle but also stable light emission across all angles, reinforcing the technology's value for high-quality display applications. These findings underscore RaDiNa's potential for significantly improving the efficiency of flexible OLEDs without altering the light emission spectrum based on the viewing angle.

Clinical overview of phototherapy for neonatal hyperbilirubinaemia.

The most efficient emission spectrum of light for phototherapy is blue-green light emission diode light with peak emission at 478 nm. In the irradiance interval of phototherapy, the relationship between efficacy and irradiance is almost linear, and it is negatively related to the haemoglobin. The action sites of phototherapy are the extravascular compartment and cutaneous blood. The most immature neonates treated aggressively had not only a lower frequency of neurodevelopmental impairment than conservatively treated, but also greater mortality. Intermittent and continuous phototherapy are assumed to be equally efficient. Home-based fibreoptic phototherapy is effective and safe. Important progress is still occurring in phototherapy.

Non-classical correlations of light in the Jaynes-Cummings model

The problems concerning the influence of spectral filters on the quantum properties of light have recently attracted great attention in connection with quantum cryptography and quantum data transmission. In this paper, we consider the influence of a spectral filter on the second-order coherence function of a field of a resonator mode and a two-level atom in the framework of the Jaynes-Cummings model. Since the Heisenberg equations for the operators of the field of the resonator mode and the atom can be solved exactly, it is possible to obtain exact analytical Fourier transformation of the dynamics of operators of the resonator mode and two-level atom. We demonstrate that the second-order coherence function of the resonator mode and the two-level atom is equal to zero for all possible frequencies in the spectrum of operator oscillations. We find the interbeam second-order coherence function between different frequencies of the Fourier spectrum and show that in the limit of a large number of quanta, it can take the values in the range from zero to two. Thus, non-classical correlations are formed between certain frequencies in the Fourier spectrum of emitted light. We demonstrate that in the limit of a large number of quanta in the resonator mode, when the filter sums up the frequencies near the resonator eigenfrequency, the second-order coherence function of the field of the resonator mode is not affected by the interaction with the two-level atom.

Establishing calibration-free pyrometry in reactive systems and demonstrating its advanced capabilities

A calibration-free multi-color pyrometry data analysis approach for determining the temporal change in the reciprocal temperature by only comparing the photomultiplier tube (PMT) responses to the system light emission is introduced. For Arrhenius reactions, analyzing the reciprocal temperature is particularly relevant for evaluating reactivity. The high accuracy of the proposed method is provided by eliminating the calibration step, which is made possible by considering the ratio of PMT signals as a function of time. The developed methodology is applicable to systems with continuous light emission spectra of the thermal nature that originate from condensed particulates. A demonstration of the data analysis approach was performed using aluminum powder burning in air. Four PMTs detected light emission during combustion that enabled analysis of six detector combinations to obtain a time-dependent signal ratio. Based on the temperature-dependent nature of light emission, the PMT response ratio provided the value of the reciprocal temperature change. All six detector combinations generated precisely coinciding results within time periods where the light emission trace behavior was relatively smooth that validated the data processing approach. It was also found that a non-smooth behavior of light emission led to significant deviations between outputs of different PMT combinations. This inconsistency between outputs was an indication of multi-temperature light emission whereas consistency between outputs corresponds to the single-temperature emission behavior. Using the calibration-free data processing approach, we isolated time periods where multi-temperature radiation is essential. Then, we further decoupled contributions from non-monotonic light emission signals and resolved two distinct temperatures responsible for observed radiation peculiarities.

Improved thermal stability and quantum efficiency of novel cyan phosphors toward full-visible-spectrum lighting

Highly efficient cyan phosphors have been identified as essential components in addressing the cyan gap present in the emission spectra of traditional white light emitting diodes. Here, we report novel Ba4Ca1-yLay(PO4)3Cl:Eu2+ (y = 0–0.15) phosphors with broadband cyan emission based on an efficient and positive cationic heterovalent substitution strategy. Under the near ultraviolet excitation, the quantum yield and thermal stability are progressively enhanced by introducing La3+ to replace the Ca2+ ions, owing to the band gap and killer centers engineering. The Ba3.92Ca0.9La0.1(PO4)3Cl:0.08Eu2+ phosphor exhibits a pronounced emission band in the cyan-green spectral range with a high internal quantum efficiency of 88.0% and an impressive external quantum efficiency of 72.1%. The utilization of Ba3.92Ca0.9La0.1(PO4)3Cl:0.08Eu2+ as the cyan emitting component in the fabrication of white light-emitting diode (WLED) has demonstrated remarkable advancements in the color rendering index value, emphasizing the potential of these phosphors for future implementation in the next generation full-visible-spectrum WLED lighting. Our findings offer evidences that defect engineering techniques effectively enhance the performance of light-emitting diode (LED) phosphors.

Proton irradiation of plastic scintillator bars for POLAR-2

POLAR-2, a plastic scintillator based Compton polarimeter, is currently under development and planned for a launch to the China Space Station in 2025. It is intended to shed a new light on our understanding of Gamma-Ray Bursts by performing high precision polarization measurements of their prompt emission. The instrument will be orbiting at an average altitude of 383 km with an inclination of 42° and will be subject to background radiation from cosmic rays and solar events. In this work, we tested the performance of plastic scintillation bars, EJ-200 and EJ-248M from Eljen Technology, under space-like conditions, that were chosen as possible candidates for POLAR-2. Both scintillator types were irradiated with 58 MeV protons at several doses from 1.89 Gy(corresponding to about 13 years in space for POLAR-2) up to 18.7 Gy, that goes far beyond the expected POLAR-2 life time. Their respective properties, expressed in terms of light yield, emission and absorption spectra, and activation analysis due to proton irradiation are discussed. Scintillators activation analyses showed a dominant contribution of β + decay with a typical for this process gamma-ray energy line of 511 keV.

Quantitative analysis of the mechanism and influencing factors of mechanical fracture-induced light emission of Zr-based bulk metallic glasses

The catastrophic fracture of bulk metallic glasses (BMGs) during mechanical deformation is generally accompanied by the unique light emission with extremely high flash temperature. This seriously endangers the application of BMGs in engineering. Without suitable quantitative characterization methods, the underlying mechanism and influencing factors of light emission remain unclear. Herein, from the perspective of photometry, a spectroradiometer is used to characterize the brightness, spectrum, and color temperature of light emission from compressive fracture of Zr-based BMGs. Specifically, the brightness physical target serves as the intensity index to quantify the variation of light emission with external conditions. The atmospheric environment compression tests are conduct to reveal the underlying mechanism of light emission generation. Moreover, the influence of sample size, strain rate and material composition on light emission is quantified by the brightness. The results reveal that the light emission from the mechanical fracture of Zr-based BMGs is due to the spontaneous combustion of sample particles with a large specific surface area and a high energy density. The energy density of fractured surfaces and elemental composition of Zr-based BMGs are intenral factors that influence light emission. Increasing the sample size or reducing the strain rate can lead to an increase in energy density, resulting in enhanced light emission. The alloy elements with high oxidation exothermic enthalpy inside the material participate in the combustion reaction of particles, which also significantly increases the intensity of light emission. These findings provide useful insights into the avoidance of mechanical fracture-induced light emission in BMG engineering applications.

Site occupancy strategy for emission tunable K3HF2W1-xOF6:xMn4+ nanophosphor via ions exchange

A novel uniformly ellipsoidal K3HF2W1-xOF6:xMn4+ nanophosphor were demonstrated by ion exchange method without K2MnF6. The samples had wide excitation range from ultraviolet to visible light and tunable emission spectra from green to red were obtained which can be regulated by the emitting spectra of K3HF2WOF6 host and Mn4+. Energy transfer efficiency from [WOF6]2− to Mn4+ were improved with the increase of Mn4+. The peak position of thermal stability spectra of K3HF2WOF6 were blueshifted while Mn4+ doped samples undergoes a redshift. The crystal field strength and the Racah parameters were estimated and luminescence mechanism was explained by the Tanabe–Sugano energy level diagram of the Mn4+. Microsecond fluorescence lifetime indicates it advantages in fast react displays to avoid ghost images. The results indicate that K3HF2W1-xOF6:xMn4+ nanophosphor has potential application in display, converting phosphors for UV and blue LED and indoor plant supplyment light.

An Innovative Fluorescent Fiber Sensor Based on Ce/Tb Co-Doped Silica Fiber for Partial Discharge Detection

A novel fluorescent fiber sensor based on cerium (Ce) and terbium (Tb) co-doped silica fiber (CTDSF) for partial discharge (PD) detection is proposed. The luminescence mechanism and PD detection principle of CTDSF are theoretically investigated. The CTDSF is fabricated using the rod-in-tube technique combined with the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser-heated drawing method. The intense emission peak of Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions located at 542 nm ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> - <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> transition) is excited at 302 nm, which indicates the energy transfer between Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Moreover, the excitation peak region near 302 nm is well aligned with the PD light emission spectrum. Subsequently, the PD time domain signals of the needle-plate defect are experimentally measured by utilizing the CTDSF sensor, high-frequency current transformer, and plastic scintillation fiber (PSF). And the experimental results demonstrate that the CTDSF sensor can detect PD signals and has an excellent PD detection linear response with a sensitivity of 0.22 ns∙V/pC. Furthermore, the sensitivity of the CTDSF sensor is approximately 2.4 times dramatically higher than that of the PSF sensor. The CTDSF sensor integrated with the all-fiber system is predicted to have a wide range of potential applications for online PD detection.

Excitation‐dependent energy transfer and color tunability in Dy3+/Eu3+ co‐doped multi‐component borophosphate glasses

AbstractUsing the melt‐quench technique, potassium zinc borophosphate (KZnBP) glasses incorporated with Dy3+, Eu3+, and Dy3+/Eu3+ ions individually and combinedly were prepared, and their photoluminescence (PL)‐related features were investigated. The KZnBP glass containing an optimized content of Dy3+ (0.5 mol%) is co‐doped with Eu3+ in various contents, and the energy transfer (ET) process between them was studied at λexci = 349, 364, 387 (Dy3+), and 394 nm (Eu3+). The Dy3+/Eu3+ co‐doped system, when excited with Dy3+ excitations has resulted in a significant decrease in the intensity of Dy3+ peaks observed at 480 nm (4F9/2→6H15/2, blue) and 574 nm (4F9/2→6H13/2, yellow), with simultaneous enhancement of the intensity of Eu3+ peaks at 591 nm (5D0→7F1, orange) and 617 nm (5D0→7F2, red). This trend is due to the efficient energy transfer from Dy3+ to Eu3+, indicating that Eu3+ ions were sensitized by Dy3+ ions. Dexter's theory and the Inokuti–Hirayama (I–H) model revealed that the dipole–dipole interaction is accountable for the energy transfer from Dy3+ to Eu3+ through energy‐transfer channels [4F9/2(Dy3+)+7F1,2(Eu3+)→6H15/2(Dy3+)+5D2(Eu3+)] and [4F9/2(Dy3+)+7F0(Eu3+)→6H13/2(Dy3+)+5D0(Eu3+)]. The color coordinates of the Dy3+/Eu3+ co‐doped glasses under various excitations fall within the white light emission spectrum, indicating their potential application in warm white LEDs.

Hartree method for molecular polaritons

The formation of the composite photonic-excitonic particle, known as a polariton, is a phenomenon emerging in materials possessing strong coupling to light. The organic-based materials besides the strong light-matter coupling also demonstrate strong interaction of electronic and vibrational degrees of freedom. We study the vibration-assisted polariton wave-function evolution treating both types of interactions as equally strong. Using the multiconfiguration Hartree approach we derive the equations of motion for the polariton wave function, where the vibration degrees of freedom interact with the polariton quantum field through the mean-field Hartree term. For the conventional quadratic polariton Hamiltonian and the Holstein-type vibration Hamiltonian (Tavis-Cummings-Holstein model), the obtained equations are in one-to-one correspondence with the original Schr\"odinger equation. In the second part of the paper, we show that our theory reproduces the physical properties of the polariton light emission spectrum. In particular, the theory explains experimental observations of the molecular Stokes shift in the polariton fluorescence spectra in the systems with strong light-matter coupling. We also investigate the behavior of the polariton wave function in the vicinity of the anticrossing point and demonstrate that the Hartree term can produce an infinite potential barrier of a dynamical origin, which is responsible for the formation of the mixed upper-lower polariton states. The nonlinear nature of the polariton theory reflects their collective behavior. We expect that the multiconfiguration Hartree approach being applied to polaritons and similar systems will result in a manifestation of new physical phenomena.

Evidence of defect-induced broadband light emission from 2D Ag-Bi double perovskites grown at liquid-liquid interfaces.

Controlling the light emission spectra of low-dimensional hybrid organic-inorganic materials remains an important goal toward the implementation of these materials into real-world optoelectronic devices. In this study, we present evidence that the self-assembly of two-dimensional (2D) silver bismuth iodide double perovskite derivatives at the interface of aqueous and organic solutions leads to the formation of defects capable of modulating the light emission spectra of these materials. Through an analysis of the structural parameters used to explain the photoluminescence (PL) spectra of 2D perovskites, we show the light spectra emitted by (4-ammonium methyl)piperidinium (4-AMP) and (3-ammonium methyl)pyridinium (3-AMPy)-spaced AgBiI8 double perovskites formed through interfacial solution-phase chemistry differ qualitatively and quantitatively from thin film samples. We use previous results to propose the differences observed in the PL spectra of different material morphologies stem from equatorial iodide vacancy formation driven by the kinetics of self-assembly at the liquid-liquid interface. These results show the generality of these chemical physics principles in the formation of defect sites in solution-processed semiconducting nanomaterials, which could help enable their broad use in optoelectronic technologies.

Chemiluminescent duplex analysis using phenoxy-1,2-dioxetane luminophores with color modulation.

Multiplex technology is an important emerging field, in diagnostic sciences, that enables the simultaneous detection of several analytes in a single sample. The light-emission spectrum of a chemiluminescent phenoxy-dioxetane luminophore can be accurately predicted by determining the fluorescence-emission spectrum of its corresponding benzoate species, which is generated during the chemiexcitation process. Based on this observation, we designed a library of chemiluminescent dioxetane luminophores with multicolor emission wavelengths. Two dioxetane luminophores that have different emission spectra, but similar quantum yield properties, were selected from the synthesized library for a duplex analysis. The selected dioxetane luminophores were equipped with two different enzymatic substrates to generate turn-ON chemiluminescent probes. This pair of probes exhibited a promising ability to act as a chemiluminescent duplex system for the simultaneous detection of two different enzymatic activities in a physiological solution. In addition, the pair of probes were also able to simultaneously detect the activities of the two enzymes in a bacterial assay, using a blue filter slit for one enzyme and a red filter slit for the other enzyme. As far as we know, this is the first successful demonstration of a chemiluminescent duplex system composed of two-color phenoxy-1,2-dioxetane luminophores. We believe that the library of dioxetanes presented here will be beneficial for developing chemiluminescence luminophores for multiplex analysis of enzymes and bioanalytes.

Energy Scales of Compositional Disorder in Alloy Semiconductors.

The study of semiconductor alloys is currently experiencing a renaissance. Alloying is often used to tune the material properties desired for device applications. It allows, for instance, to vary in broad ranges the band gaps responsible for the light absorption and light emission spectra of the materials. The price for this tunability is the extra disorder caused by alloying. In this mini-review, we address the features of the unavoidable disorder caused by statistical fluctuations of the alloy composition along the device. Combinations of material parameters responsible for the alloy disorder are revealed, based solely on the physical dimensions of the input parameters. Theoretical estimates for the energy scales of the disorder landscape are given separately for several kinds of alloys desired for applications in modern optoelectronics. Among these are perovskites, transition-metal dichalcogenide monolayers, and organic semiconductor blends. While theoretical estimates for perovskites and inorganic monolayers are compatible with experimental data, such a comparison is rather controversial for organic blends, indicating that more research is needed in the latter case.

Effect of Narrowband UV-B Irradiation on the Growth Performance of House Crickets.

Indoor co-cultivation systems can answer to the need for sustainable and resilient food production systems. Rearing organisms under light-emitting diodes (LEDs) irradiation provides the possibility to control and shape the emitted light spectra. UV-B-irradiation (280-315 nm) can positively affect the nutritional composition of different plants and other organisms, whereas information on edible insects is scarce. To evaluate the potential effect of the photosynthetically active radiation (PAR) and LED-emitting LEDs on the rearing and nutritional quality of edible insects, house crickets (Acheta domesticus) were reared from the age of 21 days under controlled LED spectra, with an additional UV-B (0.08 W/m2) dose of 1.15 KJm2 d-1 (illuminated over a period for 4 h per day) for 34 days. UV-B exposure showed no harm to the weight of the crickets and significantly increased their survival by ca. 10% under narrowband UV-B treatment. The nutritional composition including proteins, fat and chitin contents of the insects was not affected by the UV-B light and reached values of 60.03 ± 10.41, 22.38 ± 2.12 and 9.33 ± 1.21%, respectively, under the LED irradiation. Therefore, house crickets can grow under LED irradiation with a positive effect of narrowband UV-B application on their survival.

First results of fast visible imaging diagnostic in Aditya-U tokamak.

A Fast Visible Imaging Diagnostic (FVID) system, measuring the visible light emission spectrum (400-1000nm) from tokamak plasma, has been installed on the Aditya-U tokamak to monitor the two-dimensional dynamics of the poloidal cross section of the plasma. In this work, we present the design and installation of the FVID system on the Aditya-U tokamak. The evolution of plasma and plasma-wall interactions is described. The signature of the runaway electron beam in visible imaging and its correlation with other diagnostics is presented. The estimation of the electron cyclotron resonance layer position during pre-ionization is also discussed in this work.

Optimization of the Composition of Toluene-Based Liquid Scintillator

Scintillators in general and organic liquid scintillator specifically are widely used as a medium for the detection of charged particles for numerous applications in science, medicine, engineering, and other areas. The composition of the scintillator affects not only its direct performance characteristics, but also the overall cost. Optimization of this composition provides the ability to design particle detectors with an optimized light yield and emission spectra of the detection medium while optimizing the expenses at the same time. This article describes work on toluene-based liquid scintillator component optimization, where PPO is used as a fluor and POPOP as a shifter. The light yield vs. concentration and the changes in the output spectra will be presented. The empirical fit of the output spectrum using the measured contributions of the components is discussed. Further plans include the light attenuation measurements for different compositions.

Development of a Novel Highly Granular Hadronic Calorimeter with Scintillating Glass Tiles

Based on the particle-flow paradigm, a new hadronic calorimeter (HCAL) with scintillating glass tiles is proposed to address major challenges from precision measurements of jets at the future lepton colliders, such as the Circular Electron Positron Collider (CEPC). Tiles of high-density scintillating glass, with a high-energy sampling fraction, can significantly improve the hadronic energy resolution in the low-energy region (typically below 10 GeV for major jet components at Higgs factories). The hadronic energy resolution of single hadrons and the effects of key parameters of scintillating glass have been evaluated in the Geant4 full simulation, followed by the physics benchmark studies on the Higgs boson with jets in the final state. R&amp;D efforts of scintillating glass materials are ongoing within a dedicated collaboration since 2021 with the aim to achieve a high light yield, a high density, and a low cost. Measurements have been performed for the first batches of scintillating glass samples including the light yield, emission and scintillation spectra, scintillation decay times, and cosmic responses. An optical simulation model of a single scintillating glass tile has been established to provide guidance in the development of scintillating glass. Highlights of the expected detector performance and the latest scintillating glass developments are presented in this contribution.

Optical properties of low background PEN structural components for the Legend-200 experiment

Polyethylene Naphthalate (PEN) plastic scintillator has been identified as potential self-vetoing structural material in low-background physics experiments. Radio-pure scintillating components have been produced from PEN using injection compression molding technology. These low-background PEN components will be used as optically active holders to mount the Germanium detectors in the Legend-200 neutrinoless double beta decay experiment. In this paper, we present the measurement of the optical properties of these PEN components. The scintillation light emission spectrum, time constant, attenuation and bulk absorption length as well as light output and light yield are reported. In addition, the surface of these PEN components has been characterized and an estimation of the surface roughness is presented. The light output of the final Legend-200 detector holders has been measured and is reported. These measurements were used to estimate the self-vetoing efficiency of these holders.

Transcranial near-infrared light in treatment of neurodegenerative diseases.

Light is a natural agent consisting of a range of visible and invisible electromagnetic spectrum travels in waves. Near-infrared (NIR) light refers to wavelengths from 800 to 2,500 nm. It is an invisible spectrum to naked eyes and can penetrate through soft and hard tissues into deep structures of the human body at specific wavelengths. NIR light may carry different energy levels depending on the intensity of emitted light and therapeutic spectrum (wavelength). Stimulation with NIR light can activate intracellular cascades of biochemical reactions with local short- and long-term positive effects. These properties of NIR light are employed in photobiomodulation (PBM) therapy, have been linked to treating several brain pathologies, and are attracting more scientific attention in biomedicine. Transcranial brain stimulations with NIR light PBM in recent animal and human studies revealed a positive impact of treatment on the progression and improvement of neurodegenerative processes, management of brain energy metabolism, and regulation of chronic brain inflammation associated with various conditions, including traumatic brain injury. This scientific overview incorporates the most recent cellular and functional findings in PBM with NIR light in treating neurodegenerative diseases, presents the discussion of the proposed mechanisms of action, and describes the benefits of this treatment in neuroprotection, cell preservation/detoxification, anti-inflammatory properties, and regulation of brain energy metabolism. This review will also discuss the novel aspects and pathophysiological role of the glymphatic and brain lymphatics system in treating neurodegenerative diseases with NIR light stimulations. Scientific evidence presented in this overview will support a combined effort in the scientific community to increase attention to the understudied NIR light area of research as a natural agent in the treatment of neurodegenerative diseases to promote more research and raise awareness of PBM in the treatment of brain disorders.