Mechanism Of Light Emission Research Articles

Harvesting the tuning mechanism of strategic polychrome and white light emission in NapH dye based on excited state intermolecular proton transfer

Organic white light emitting (WLE) materials have sparked a research boom due to their promising applications in display devices, artificial lighting, and molecular sensors. However, the complex luminescence mechanism of full-spectra emitting materials has limited the development of white light materials with high stability and reproducibility. In this study, building on the full-spectra luminescent naphthimide dye (NapH) introduced by Xu et al., (Chin. Chem. Lett. 35(2024), 108348), we report the solvent-sensitive excited state proton transfer (ESPT) properties and white light emission mechanism in NapH. Our theoretical research results show that the ESPT process of NapH molecule is hindered in the low-polar solvent tetrahydrofuran (THF), so only the blue fluorescence from the Enol* is observed in the experiment. In contrast, in polar solvents such as water (H2O) and methanol (MeOH), the formation of strong intermolecular hydrogen bonds successfully initiates the ESPT process, leading to the dual fluorescence observed in experiments, with blue emission from the Enol* and red emission from the Nap anion. In essence, different solvent environments can adjust several emission colors. Furthermore, we theoretically verify that the optimal white light emission can be achieved when the mixed solvent ratio of dimethyl sulfoxide (DMSO) and dioxane (DIOX) is 5:5, which aligns well with experimental results. More importantly, we elucidate the specific WLE mechanism from multiple perspectives, including potential energy curves and electron spectra. Our work not only displays the interaction models of NapH molecule in various solvents, but also reveals the underlying luminescence mechanism, thus providing a valuable theoretical reference for the development and advancement of new white light materials.

CAFFEIC ACID STIMULATES IN VIVO LUMINESCENCE OF THE MYCELIA OF THE HIGHER FUNGI NEONOTHOPANUS NAMBI AND ARMILLARIA BOREALIS

CAFFEIC ACID STIMULATES IN VIVO LUMINESCENCE OF THE MYCELIA OF THE HIGHER FUNGI NEONOTHOPANUS NAMBI AND ARMILLARIA BOREALIS

Influence of the substrate conductivity type on the electroluminescence properties of PP+IN and PIN+N diodes based on amorphous silicon carbide (a-Si1-xCx:H) / crystalline silicon (c-Si) heterostructures

The study of the conduction and light emission mechanisms of PIN diodes based on amorphous silicon-carbide (a-Si1-xCx:H) thin film and crystalline silicon (c-Si) substrates is reported in this work. Using the same low-temperature process (200 °C), PP+IN and PIN+N structures were fabricated on p-type and n-type silicon (Si) substrates, respectively. The plasma enhanced chemical vapor deposition (PECVD) technique was employed for the active layers deposition where two different CH4/SiH4 flow rates ratios of 30 sccm/6 sccm and 30 sccm/1 sccm were used. All structures show red-orange light emission in forward bias (FB). The structures with the active layer deposited with a lower SiH4 flow rate, display light emission with a higher intensity at a lower voltage bias.In addition, we related the current-voltage measurements with different conduction models and the dominant charge transport mechanisms in the PIN structures were proposed. The highest Si content structures were related to Fowler-Nordheim (F-N) tunneling, because of its active layer with lower barrier height. On the other hand, the lowest Si content structures were associated with the Poole-Frenkel (P-F) emission, due to a higher density of defects in localized tail states. The results showed the same conduction and emission mechanisms for the PP+IN and PIN+N diodes with the same active layer, regardless of the conduction type of substrate, proving that it is feasible to use the same process for developing light emission devices on p-type and n-type Si substrates.

A review of colored light production by pyrotechnic materials

AbstractPyrotechnics are a unique set of materials because they can be formulated to control combustion behavior to elicit desired effects such as light emission, smoke formation, and noise. The ability to enhance and control light emission is particularly desirable for entertainment purposes, as well as military applications. Designing such materials for high color purity at a specific wavelength requires an understanding of the different factors that affect their performance. This review will cover the various aspects of color production, including light emission mechanisms, components of a color composition, and key parameters that determine the optical wavelength band for these compositions. Additionally, because conventional pyrotechnic formulations are known to produce toxic emissions, less hazardous and sustainably formulated pyrotechnics for color production will also be reviewed. Finally, a short perspective is presented on the possible extension of pyrotechnic applications beyond conventional, civilian, and military purposes.

Theoretical study of the electronic and optical properties of ZnO/MgO rock salt superlattices

An analysis of some electronic and optical properties of rock salt (RS) ZnO/MgO superlattices related to potential applications in optoelectronics and electronics is carried out.In order to find possible light emission mechanisms, the electronic band structure, projected and k-resolved projected density of states and optical parameters such as the refractive index, reflection and absorption coefficients are calculated.We show that the bandgap of the RS ZnO/MgO superlattice is indirect for all considered thicknesses of quantum wells and barriers. Despite the indirect character of the bandgap, other features of the studied superlattice, such as the flat character of the top of the valence band and the bottom of the conduction band, combined with strong electron-phonon coupling and high exciton binding energy, may indicate the possibility of light emission similar to that in hexagonal BN.

Structure elucidation of Keroplatus (Diptera:Keroplatidae) fungus gnat oxyluciferin

Bioluminescence of insects is a well-known natural phenomenon in the focus of interest of scientific research. While the mechanisms of bioluminescence in Coleoptera have been extensively studied, there is a lack of information about the chemistry of light emission in Diptera species. Here we report the Keroplatus spp. oxyluciferin structure elucidation and identification as 3-hydroxykynurenic acid. Additionally, the present study provides the first direct evidence of the relationship between the bioluminescent systems of Orfelia and Keroplatus. However, the properties of the putative Orfelia oxyluciferin suggest that the light emission mechanisms are not identical.

Tunable dual color emission from the opposite faces of silicon nanoparticle embedded gel-glass

A luminescent silicon nanoparticle embedded gel-glass, prepared by room temperature hydrolysis and reduction of aminosilane, exhibits intriguing dual photoluminescence (PL) from opposite faces of the glass. The face, which is excited with UV, exhibits excitation energy dependent blue-green emission. As the excitation energy is varied from 350 nm to 450 nm the PL peaks shift from 435 nm to 506 nm. The opposite surface, on the other hand emits nearly excitation independent green light – the PL peak shifts by ∼17 nm as the excitation energy is varied from 350 nm to 450 nm. The luminescent properties provide interesting insights into the light emission mechanism from nanostructured silicon. Spectral filtering by reabsorption and photon reabsorption-reemission in a size distributed nanoparticle system having different optical gaps play a combined role in the observed dual emission. We show that the dual emission can be tuned by simply varying the thickness of the glass. Such dual emission renders the luminescent glass amenable for several applications as a novel solid state display material.

Low-Temperature Photoluminescence Dynamics Reveal the Mechanism of Light Emission by Colloidal CuInS2 Quantum Dots

Copper indium sulfide colloidal quantum dots are in focus of the nanocrystal community as their optical properties make them exciting candidates for applications in bioimaging and biosensing, solar cells, luminescent solar concentrators, and lighting. However, fulfilling this application potential is hampered by poor understanding of the mechanism of light emission by these dots. In this work, we study temperature and magnetic field dependent photoluminescence (PL) dynamics and spin dynamics at cryogenic temperatures. We cast our experimental observations against two prevailing models of PL in CuInS2 quantum dots: an excitonic mechanism and a free-to-bound mechanism, in which a delocalized electron recombines with a hole localized at a copper ion. We unambiguously show that the PL occurs as the result of the free-to-bound mechanism.

Light emission mechanisms from graphene: A review

This paper reviews the various experiments and proposed mechanisms of light emission from graphene from recent research. Due to graphene’s combination of exceptional mechanical, electronic, and optical properties, graphene shows promise for emerging optoelectronic and photonics applications, such as light emitting devices, solar cells, photodetectors, and plasmonic devices. Various types of light emission have been demonstrated, from graphene and graphene-related structures (e.g. graphene oxide and graphene quantum dots) with promise for applications such as drug delivery, light emitting diodes, and sensors. Several different routes to graphene light emission have been experimentally demonstrated or theorized over the last several years. Light emission mechanisms that will be discussed in this work include photoluminescence, electroluminescence, thermal emission, surface plasmon-electron interaction and the Quantum Čerenkov effect.

Light emission mechanism in dimers of carbene-metal-amide complexes.

Recently an efficient dual electroluminescence from monomers and dimers was observed among the structural examples of the emerging emitter class of carbene-metal-amides (CMAs), allowing the preparation of simple design white organic light emitting diodes (wOLEDs). Here we investigate in detail the light emission mechanism in the dimeric species of CMA emitters on the basis of a copper(I) complex TCP bearing thiazoline carbene and 10H-phenothiazine 5,5-dioxide (Ptz) ligands. The X-ray structure for crystals with dimer-only emission was obtained, revealing that emissive aggregates consist of face-to-face stacked molecular pairs with an intermolecular distance of 3.673 Å. The close packing is aided by reduced sterical bulk at the carbene ligand, as well as by a torsional twist between the carbene and amide fragments. Experimental and computational data show that the emission mechanism in aggregates is related to the formation of a persistent dimer, not the excimer. Radiative relaxation proceeds through an intermolecular charge transfer process between the carbene and amide ligands of the neighbouring molecules. In comparison to the monomer, the thermally activated delayed fluorescence (TADF) process in the dimer is characterized with significantly higher energy gaps (ΔEST) between the lowest singlet (S1) and triplet (T1) excited states. At the same time the aggregated species exhibit a significantly increased phosphorescence rate (τ = 12 μs at 10 K temperature) due to the presence of two metal atoms, resulting in a sixfold increase in the spin-orbit coupling (SOC) matrix element in comparison to the monomer.

Система цитохрома Р450 может участвовать в светоизлучении высших грибов

The paper presents data that testify in favor of the participation of the cytochrome P450 system in the light emission of higher fungi. Extracts from mycelia of different species of luminous basidiomycetes containing fungal luminescent systems that provide luminescence in vitro were obtained. Applied conditions for the isolation of luminescent systems (sonication, centrifugation at 40000g) indicate the presence of membrane structures in the extracts, in particular, microsomes formed as a result of ultrasonic disintegration of the endoplasmic reticulum (ER). Differential spectral analysis of the extracts revealed the presence of two absorption peaks at 410 nm and 450 nm, which indicates the presence of cytochromes b5 and P450. The luminescence of the extracts is stimulated by reduced pyridine nucleotides, however, the addition of NADPH causes a higher level of luminescence compared with NADH. The addition of hydrogen peroxide significantly (from several times to 1-2 orders of magnitude) increases the luminescence intensity of extracts activated by NAD(P)H. The addition of fluconazole significantly inhibits the light emission of extracts. The data obtained indicates that the cytochrome P450 system associated with ER membranes may participate in the mechanism of light emission of higher fungi with the involvement in the process of electron transport enzyme systems: NADPH-dependent reductase of cytochrome P450 - cytochrome P450 and NADH-dependent reductase of cytochrome b5 - cytochrome b5 - cytochrome P450. In this case, cytochrome P450 may hydroxylate hispidin (precursor of the luminescent reaction substrate) to form luciferin and catalyze its oxidation in the presence of ROS with light emission.

Exploration of the effect of blue laser light on microRNAs involved in functional metabolism in D. officinale through RNA sequencing

Dendrobium officinale has remarkable medicinal functions and high economic value. Laser light sources are different from ordinary light sources in terms of the light emission mechanism and play important roles regulating functional metabolite synthesis in D. officinale. However, the mechanism by which miRNAs participate in regulating the D. officinale response to blue laser irradiation has not been reported. Previous studies found that the number of red leaves on plants treated with blue laser light was greater than that on plants treated with blue light and white light, and blue laser light was most effective at promoting the accumulation of total flavonoids, polysaccharides and alkaloids. RNA-seq was used to analyse the difference in the effects of lasers on D. officinale. KEGG analysis of the target genes of differentially expressed (DE) miRNAs showed that there were multiple blue laser response pathways, among which peroxisome, nitrogen metabolism, terpenoid biosynthesis, porphyrin and chlorophyll metabolism played central roles. Cytoscape interaction analysis of DE miRNA targets showed that novel_miR_248 most likely participates in the influence of blue laser irradiation on D. officinale. Content verification in D. officinale showed that blue laser light could also increase the total terpene, chlorophyll levels, nitrate reductase, glutamine synthase and glutamate dehydrogenase. Combined with the qPCR results, these findings showed that miR395b, miR827 and miR319l may participate in the blue laser signalling network through their target genes and then regulate the accumulation of functional metabolites in D. officinale. This study provides a scientific basis for the high-yield production of D. officinale.

Tuning Light Emission Crossovers in Atomic-Scale Aluminum Plasmonic Tunnel Junctions.

Atomic-sized plasmonic tunnel junctions are of fundamental interest, with great promise as the smallest on-chip light sources in various optoelectronic applications. Several mechanisms of light emission in electrically driven plasmonic tunnel junctions have been proposed, from single-electron or higher-order multielectron inelastic tunneling to recombination from a steady-state population of hot carriers. By progressively altering the tunneling conductance of an aluminum junction, we tune the dominant light emission mechanism through these possibilities for the first time, finding quantitative agreement with theory in each regime. Improved plasmonic resonances in the energy range of interest increase photon yields by 2 orders of magnitude. These results demonstrate that the dominant emission mechanism is set by a combination of tunneling rate, hot carrier relaxation time scales, and junction plasmonic properties.

Role of High Nitrogen‐Vacancy Concentration on the Photoluminescence and Raman Spectra of Diamond

A photoluminescence (PL) and Raman spectroscopy study of various diamond samples that have high concentrations of nitrogen‐vacancy (NV) color centers up to multiple parts per million (ppm) is presented. With green, red, and near‐infrared (NIR) light excitation, it is demonstrated that while for samples with a low density of NV centers the signals are primarily dominated by Raman scattering from the diamond lattice, for higher density of NVs, a combination of Raman scattering from the diamond lattice and fluorescence from the NV centers is observed, while for the highest NV densities the Raman signals from diamond are completely overwhelmed by the intense NV's fluorescence. However, under NIR excitation, Raman diamond signatures can be observed for some diamonds. These observations reveal different roles of two mechanisms of light emission and contradict the naïve belief that Raman scattering enables the complete characterization of a diamond crystalline sample.

Differences of the intensity increase of optical signals with fluorescein between Cherenkov-light and luminescence of water

The imaging of the luminescence of water and Cherenkov-light with fluorescein during irradiation is a useful method to increase intensity; however, the magnitudes of the increase in intensity for Cherenkov-light and luminescence of water have been neither evaluated nor compared. Therefore, we measured the Cherenkov-light and luminescence of water with and without fluorescein during irradiation, and then we compared the magnitudes of the intensity increase with fluorescein. For 6 and 10 MV X-rays as well as 6 and 12 MeV electrons, the intensity of the Cherenkov-light images increased only 2 to 3 times with fluorescein water compared with that of water. Meanwhile, for 100 kV X-rays and 150 MeV protons, the intensity of the luminescence images increased more than 10 times with fluorescein water compared with that of water. The difference could probably be attributed to the difference in the light-emission mechanisms and coherency between Cherenkov-light and the luminescence of water.

(Invited) Broadband Electroluminescence from Reverse Breakdown in Individual Suspended Carbon Nanotube Pn-Junctions

There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral emission characteristics that provide important information regarding the underlying physical processes that lead to photon emission. Here, we report spectra obtained from individual suspended CNT dual-gate field effect transistor (FET) devices under different gate and bias conditions. By applying opposite voltages to the gate electrodes (i.e., Vg1 = –Vg2), we are able to create a pn-junction within the suspended region of the CNT. Under forward bias conditions, the spectra exhibit a peak corresponding to E11 exciton emission via thermal (i.e., blackbody) emission occurring at electrical powers around 8 μW, which corresponds to a power density of approximately 0.5 MW/cm2. On the other hand, the spectra observed under reverse bias correspond to impact ionization and avalanche emission, which occurs at electrical powers of ~ 10 nW and exhibits a featureless flat spectrum extending from 1,600 nm to shorter wavelengths up to 600 nm. Here, the hot electrons generated by the high electric fields (~ 0.5 MV/cm) are able to produce high energy photons far above the E11 (ground state) energy. It is somewhat surprising that these devices do not exhibit light emission by the annihilation of electrons and holes under forward bias, as in a light emitting diode (LED). Possible reasons for this are discussed, including Auger recombination.DOI: 10.1007/s12274-020-2941-3 Figure 1

(Invited) Light-Emitting Devices Based on Defect-Enhanced Group-IV Nanostructures

Combining Si-based integrated optics with Si-based microelectronics is crucial for next-generation applications ranging from data transfer on short distances to sensing and, potentially, to quantum cryptography at telecom wavelengths. However, Si's intrinsically poor light-emitting properties, i.e., its indirect energy bandgap, inhibit a straightforward implementation of telecom devices such as light-emitting diodes and lasers operating at room temperature.We argue that adding Ge heterostructures, nanostructures, intentionally-induced defects, and defects within nanostructures to the Si platform can be a viable way to overcome the limitations of Si as a light-emitting material [1]. Significant progress for light-emission from group-IV nanostructures can be achieved by intentionally incorporating extended point defects inside the QDs upon in-situ low-energy ion implantation [2],[3]. This work discusses the superior light-emission properties from such defect-enhanced quantum dots (DEQDs) and our present understanding of their structural formation and light-emission mechanisms [4], indicating that optically direct recombination paths play a role in room-temperature light emission.As compared to other group-IV systems with pronounced optical emission, contact doping and hence fabrication of electrically driven devices is relatively straightforward in this nanosystem since DEQDs are embedded into a defect-free Si matrix [5],[6]. We show that useful electrically driven devices, such as light-emitting diodes (LEDs), can be fabricated employing optically active DEQD material. These LEDs exhibit exceptional temperature stability of their light-emission properties even up to 100°C, unprecedented for purely group-IV-based optoelectronic devices [7]. We discuss the role of vital parameters, such as the temperature stability of the structural properties [8],[9], the scalability of the light-emission with the nanostructure density [6], and passivation schemes to further improve the optical properties [8],[10]. Additionally, we elaborate on schemes for advanced layouts for electrically-pumped devices.References[1 ] M. Brehm, Silicon Photonics IV, 67-103, Silicon Photonics IV: Innovative Frontiers, edited by David J. Lockwood and Lorenzo Pavesi, Springer series Topics in Applied Physics (2021).[2] M. Grydlik et al., ACS Photonics 3, 298–303 (2016).[3] M. Grydlik et al., Nano Lett. 16, 6802–6807 (2016).[4] F. Murphy-Armando et al., Phys. Rev. B 103, 085310 (2021).[5] M. Brehm and M. Grydlik, Nanotechnology 28, 392001 (2017).[6] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[7] P. Rauter et al., ACS Photonics 5, 431-438 (2018).[8] L. Spindlberger et al., Crystals 10, 351 (2020).[9] L. Spindlberger et al., Physica Status Solidi (a) 216, 1900307 (2019).[10] L. Spindlberger et al., Appl. Phys. Lett. 118, 083104 (2021).

Light emission of Zr-based bulk metallic glass during high-speed cutting: From generation mechanism to control strategies

Light emission is a unique machining feature during high-speed cutting of Zr-based bulk metallic glass (BMG), which significantly deteriorates the machining quality and efficiency. However, its generation mechanism is still unclear. In this study, the light emission of Zr-based BMG during high-speed cutting was quantified photometrically, and its correlation with cutting energy was investigated. The chemical composition change and the formation process of luminescent particles were analyzed. The generation mechanism of light emission was subsequently revealed. It was found that the light emission is due to the spontaneous ignition in air of Zr-based BMG particles with large specific surface area, produced by ductile tearing of the bottom of the chip. The friction energy of the tool-chip interface flowing into the chips is the dominant factor that triggers particle combustion. Therefore, from the perspective of controlling tool wear, machining strategies with controllable light emission were proposed. In order to suppress light emission, the primary method is to decrease the cutting speed and feed. The second is to improve the chip removal ability and the wear resistance of the tool. Cutting oil is only effective for suppressing light emission at low cutting speeds, while liquid nitrogen is not suitable for cutting Zr-based BMG due to increased tool wear. The findings of this work contribute to a deeper understanding of the generation mechanism of cutting features in glassy metals, and provide guidance for high-speed cutting process optimization of Zr-based BMG.

Crystal Prediction and Design of Tunable Light Emission in BTB‐Based Metal‐Organic Frameworks

AbstractMetal‐organic frameworks (MOFs) have recently been shown to exhibit unique mechanisms of luminescence based on charge transfer between structural units in the framework. These MOFs have the potential to be structural tuned for targeted emission with little or no metal participation. A computationally led, material design and synthesis methodology is presented here that elucidates the mechanisms of light emission in interpenetrated structures comprised of metal centers (M = In, Ga, InGa, InEu) and BTB (1,3,5‐Tris(4‐carboxyphenyl)benzene) linkers, forming unique luminescent M‐BTB MOF frameworks. Gas phase and periodic electronic structure calculations indicate that the intensity of the emission and the wavelength are overwhelmingly controlled by a combination of the number of interacting stacked linkers and their interatomic spacings, respectively. In the MOF, the ionic radii of the metal centers primarily control the expansion or shrinkage of the linker stacking distances. Experimentally, multiple M‐BTB‐based MOFs are synthesized and their photoluminescence was tested. Experiments validated the modeling by confirming that shifts in the crystal structure result in variations in light emission. Through this material design method, the mechanisms of tuning luminescence properties in interpenetrated M‐BTB MOFs have been identified and applied to the design of MOFs with specific wavelength emission based on their structure.

Photoluminescence of Cis-Polyacetylene Semiconductor Material

Photoluminescence (PL) is one of the key experimental characterizations of optoelectronic materials, including conjugated polymers (CPs). In this study, a simplified model of an undoped cis-polyacetylene (cis-PA) oligomer was selected and used to explain the mechanism of photoluminescence (PL) of the CPs. Using a combination of the ab initio electronic structure and a time-dependent density matrix methodology, the photo-induced time-dependent excited state dynamics were computed. We explored the phonon-induced relaxation of the photoexcited state for a single oligomer of cis-PA. Here, the dissipative Redfield equation of the motion was used to compute the dissipative excited state dynamics of electronic degrees of freedom. This equation used the nonadiabatic couplings as parameters. The computed excited state dynamics showed that the relaxation rate of the electron is faster than the relaxation rate of the hole. The dissipative excited-state dynamics were combined with radiative recombination channels to predict the PL spectrum. The simulated results showed that the absorption and emission spectra both have a similar transition. The main result is that the computed PL spectrum demonstrates two mechanisms of light emission originating from (i) the inter-band transitions, corresponding to the same range of transition energies as the absorption spectrum and (ii) intra-band transitions not available in the absorption spectra. However, the dissipative Redfield equation of the motion was used to compute the electronic degrees of freedom of the nonadiabatic couplings, which helped to process the time propagation of the excited dynamic state. This excited dynamic state shows that the relaxation rate of the electron is faster than the relaxation rate of the hole, which can be used for improving organic semiconductor materials for photovoltaic and LED applications.