Characteristic Emission Spectra Research Articles

Luminescent rare earth complexes of Ce3+, Eu2+and Yb2+with spiro-bis(pyrazolyl)borate ligands containing C–H···M interactions

Luminescent rare earth complexes based on interconfigurational 5d-4f transition have characteristics of adjustable emission spectra and short excited state lifetimes, showing potential applications in display, lighting and other fields. In this work, nine Ce3+, Eu2+ and Yb2+ complexes with spiro-bis(pyrazolyl)borate ligands, where pyrazolyl stands for pyrazolyl, 3-methylpyrazolyl, or 3,5-dimethylpyrazolyl, were designed and synthesized. Ce3+ complexes show emission colors of blue, with photoluminescence quantum yields (PLQYs) of 94%–100%; Eu2+ complexes show emission colors of yellow-green, with PLQYs of 60%–78%; Yb2+ complexes show emission colors of orange or red, with PLQYs of 3%–4%. In addition, the crystal structures and theoretical calculation results show C–H···M interactions between bridge-head H atoms of the spirane and central metal ions in these complexes. It is found that the introduction of spirane with large steric hindrance and the existence of C–H···M interactions can improve the stability of the complexes in air atmosphere.

Red emission enhancement in BaYF5:Eu3+ phosphor nanoparticles by Bi3+ co-doping.

Herein, we report the photoluminescence properties of Bi3+-sensitized BaYF5:10 mol%Eu3+ nanoparticles. The emission spectra feature Eu3+ peaks corresponding to transitions from the 5D0 excited to 7FJ (J = 1, 2, 3, 4) lower levels with two dominant emissions positioned in the orange-red (∼ 592 nm, 5D0 → 7F1) and deep-red (∼ 697 nm, 5D0 → 7F4) regions. Upon 265 nm excitation, the emission intensity increases with an increase of Bi3+ concentration up to 20 mol%. Due to the energy transfer from Bi3+ to Eu3+ ions, the integrated intensity of Eu3+ emission in the Bi3+ co-doped BaYF5:10 mol%Eu3+ is 216% stronger than in the Bi3+-free sample. Our findings demonstrated that BaYF5:Eu,Bi has potential in plant lighting technology due to strong emission in red and deep-red spectral areas.

Experimental investigation of OH* emission spectrum characteristics and transient ignition dynamics in methane and coal dust mixtures explosions

Combustible gases, dusts and their mixtures are widely present in human production and life，and the fire and explosion disasters caused by them pose a serious threat to the field of energy security applications. Studying the ignition process of mixtures is essential for disaster risk assessment and safety protection. In this work, the explosion characteristics and OH* emission spectra of the mixtures were experimentally tested by varying the fuel equivalence ratio ( ER ≈ 0.79 ∼ 1.71), and the evolution of the transient flow field structure during the ignition process was quantitatively analyzed using the schlieren image velocimetry method. The results indicate that the emission spectrum of OH* is closely correlated with the maximum explosion pressure, and the spectral intensity of OH* at 306.4 nm is consistent with the maximum rate of explosion pressure rise. The flow field during the ignition process of the mixtures shows that a small amount of coal dust (concentration≤30 g/m3) can significantly promote flame acceleration and instability as the methane concentration is in lean combustion or stoichiometric ratio. However, when the concentration of coal dust increases (concentration≥40 g/m3), coal dust will suppress flame acceleration and instability. For methane concentration in fuel-rich combustion state, coal dust always suppresses flame acceleration and instability. The experimental results contribute to a further understanding of gas and coal dust mixed explosions and provide a verification database for the construction of chemical kinetic mechanisms.

Exploring the viability of thermally robust β-BaB2O4: Dy3+ through FIR based polynomial approach for advanced temperature sensing and WLED applications

In this present work, we have explored the optical, structural, and thermal sensing properties of novel β-BaB2O4: xDy3+ (x = 1, 2, 3, 4, and 5 mol%) phosphors prepared using the solid-state reaction method. The optimization of the phosphors was achieved by using the characteristic emission spectra of Dy³⁺ ions. A thorough investigation was conducted into the various mechanisms contributing to concentration quenching, including cross-relaxation pathways, multipole-multipole interactions, and non-radiative energy transfer processes. Using the diffused reflectance spectra, significant parameters including optical band gap, nephelauxetic ratio, bonding parameter, and refractive index were evaluated. Temperature-dependent optical properties revealed a very high quenching temperature of 492.7 K. Using the florescent intensity ratio (FIR) with polynomial fit from 2nd to 5th order, the highest absolute sensitivity was obtained as 0.0472 K−1 at 483 K, and the highest relative sensitivity of 0.3922 % K−1 at 303 . Finally, the optimized phosphor exhibited exceptional thermal stability up to 500˚C with nearly 1 wt% of loss.

In-situ observation of heavy ion beam-induced luminescence of Al2O3 (Cr3+) in a 0 - 10 T magnetic field background.

High energy density physics driven by intense heavy ion beams will be an important new project for the high intensity heavy-ion accelerator facility and the Dongjiang Laboratory. This paper presents an experimental investigation of ion beam-induced luminescence in a strong magnetic field background at HIRFL. The experiment utilizes a 430 MeV/u 84Kr26+ ion beam with a pulse duration of 300 ns to bombard an Al2O3 (Cr3+) solid target. The results show that the characteristic emission spectrum of the Cr3+ ion's 2E→4A2 transition is observed, and spectrum parameters significantly change with the magnetic field of the background. We present the experimental data on the shifts of the peak center (Δσave) and the broadening of full width at half maximum (WG). The changes in parameters related to the intensity of the magnetic field are discussed using atomic models. This work demonstrates the potential application of diagnosing magnetic fields by measuring characteristic spectra.

The Influence of Thickness and Spectral Properties of Green Color-Emitting Polymer Thin Films on Their Implementation in Wearable PLED Applications.

A systematic investigation of optical, electrochemical, photophysical, and electrooptical properties of printable green color-emitting polymer (poly(9,9-dioctylfluorene-alt-bithiophene)) (F8T2) and spiro-copolymer (SPG-01T) was conducted to explore their potentiality as an emissive layer for wearable polymer light-emitting diode (PLED) applications. We compared the two photoactive polymers in terms of their spectral characteristics and color purity, as these are the most critical factors for wearable lighting sources and optical sensors. Low-cost, solution-based methods and facile architecture were applied to produce rigid and flexible light-emitting devices with high luminance efficiencies. Emission bandwidths, color coordinates, operational characteristics, and luminance were also derived to evaluate the device's stability. The tuning of emission's spectral features by layer thickness variation was realized and was correlated with the interplay between H-aggregates and J-aggregates formations for both conjugated polymers. Finally, we applied the functional green light-emitting PLED devices based on the two studied materials for the detection of Rhodamine 6G. It was determined that the optical detection of the R6G photoluminescence is heavily influenced by the emission spectrum characteristics of the PLED and changes in the thickness of the active layer.

Acoustic emission spectrum characteristics of structural coal destruction in negative pressure environment

Abstract The uniaxial compression experiments under a low-pressure environment were performed by using structural coal samples. The frequency domain response characteristics of coal mass failure under loading in a low-pressure environment were acquired by FFT transformation and wavelet packet decomposition. The results show: As the loading stress of coal increases, the AE spectrum becomes more abundant, and the whole AE spectrum shows a left-shift trend. When the gas pressure increases, the acoustic emission signals change from low-frequency high-energy to high-frequency low-energy, the frequency band gradually narrates, and the spectrum changes from complex multi-peak shape to single-peak shape. As stress increases, the proportion of energy in the band 0-4.38 kHz gradually increases, while that in other bands gradually decreases. The energy response to stress changes in the two frequency bands of 2.92-4.38 kHz and 4.38-5.84 kHz is the most obvious. When the pressure changes, the energy in three frequency bands of 2.92-4.38 kHz, 4.38-5.84 kHz, and 7.3-8.76 kHz present an evident response trend with the pressure change, and the response trend (increase) of the latter two is exactly opposite (decrease) to that of the former. This phenomenon indicates that 2.92-4.38 kHz and 4.38-5.84 kHz are the characteristic frequency bands of the coal fracture process. The findings of this research offer crucial foundational data to support the monitoring and early warning of coal and gas outburst hazards.

Porphyrin Production by Corynebacterium diphtheriae Strains from Clinical Isolates.

Porphyrins are intermediate metabolites involved in the biosynthesis of vital molecules, including heme, cobalamin, and chlorophyll. Bacterial porphyrins are known to be proinflammatory and are associated with biofilm formation. This study investigated porphyrin production by strains of Corynebacterium diphtheriae using emission spectroscopy, high-performance liquid chromatography with fluorescence detection, diode array detector, and mass spectrometry. Emission spectroscopy revealed characteristic porphyrin emission spectra in all strains, with coproporphyrin III predominating. Qualitative analysis by different chromatographic methods identified coproporphyrin III, uroporphyrin I, and protoporphyrin IX in all strains. Quantitative analysis revealed strain-dependent coproporphyrin III production. Further studies are required to investigate the relationship between porphyrin production and the virulence potential of Corynebacterium diphtheriae.

Phase identification and photophysical characteristics of vanadate-based nanophosphors for lighting and latent fingerprinting applications

Monoclinic structure-based Er3+-activated Ba2BiV3O11 nanophosphors have been developed via an easy and cost-efficacious urea-aided solution combustion (SC) procedure. Various spectroscopic and structural investigations thoroughly examine the produced powders. The crystal structure has been resolved by employing a combination of X-ray diffraction (XRD) and the Rietveld refinement practice. The developed powdered nanosamples are crystallized in a monoclinic crystal system with P21/a space group. Further, to evaluate the composition of elements and their relative distribution, energy dispersive X-ray (EDAX) analysis was performed. The band gap values for the host matrix and the optimal nanophosphors were measured using a DR spectrophotometer; the obtained values were 3.47 eV and 3.40 eV, respectively. The strongest excitation peak at 381 nm is closely-matched with the characteristic wavelength of commercialized near ultraviolet (NUV) based LEDs. The characteristic emission spectra of Ba2Bi1-xErxV3O11 (x = 0.01–0.1) phosphors show the strongest emission at 553 nm (4S3/2 → 4I15/2). Additionally, photometric parameters such as quantum efficiency (86 %), color coordinates (x = 0.2568 and y = 0.4551), and correlated color temperature (CCT = 7722 K) are obtained from PL data and are strongly advised for use in wLEDs, color displays, imaging, lighting, and latent fingerprint applications.

Development of white organic light emitting diodes based on carbazole-derived compounds

The object of research is the thermal, photophysical, and electrophysical properties of newly synthesized carbazole-derived compounds and organic light-emitting structures based on them. The problem consists in the comprehensive solution of scientific and technical problems of improving the characteristics of white organic light-emitting diodes (OLED), expanding their emission spectrum, improving color and energy characteristics. The results of the thermal, electrophysical and photophysical properties of the investigated carbazole compounds were obtained. They demonstrated good thermal stability. Absorption spectra in solid films were recorded in the range of 300–350 nm. Photoluminescence spectra were observed at a wavelength of 407 nm for the first and second compounds and 430 nm for the third. The quantum yield of photoluminescence in films for compounds 1, 2, and 3 was 16 %, 7 %, and 7 %, respectively. Organic light-emitting structures of white emission color with color coordinates (0.31, 0.35), (0.32, 0.34) and (0.38, 0.34) close to natural white light (0.33, 0.33) were formed using the thermovacuum sputtering method. The turn-on voltage of the white OLED is 6 V, the maximum brightness of the light-emitting structures was 10,000 cd/m2. The devices demonstrated a sufficiently high external quantum efficiency of 5 % to 7 %. The obtained results are explained by the mixing of different types of electroluminescence, namely excitonic and electromeric. Electromeric radiation is obtained due to transport layers. This approach improves such an important parameter of white light as its quality, which includes color coordinates and color rendering index. Due to their color characteristics, white light-emitting diodes based on carbazole-derived compounds are promising candidates for use in modern lighting systems. A separate advantage of these light-emitting structures is the dependence of the color gamut of their radiation on the applied voltage. In addition, organic LEDs based on carbazole-derived compounds have low energy consumption and are environmentally friendly due to the absence of toxic substances in their design, which creates prerequisites for both global energy savings and a reduction of the industrial burden on the environment.

Nanocavity-Mediated Purcell Enhancement of Er in TiO2 Thin Films Grown via Atomic Layer Deposition.

The use of trivalent erbium (Er3+), typically embedded as an atomic defect in the solid-state, has widespread adoption as a dopant in telecommunication devices and shows promise as a spin-based quantum memory for quantum communication. In particular, its natural telecom C-band optical transition and spin-photon interface make it an ideal candidate for integration into existing optical fiber networks without the need for quantum frequency conversion. However, successful scaling requires a host material with few intrinsic nuclear spins, compatibility with semiconductor foundry processes, and straightforward integration with silicon photonics. Here, we present Er-doped titanium dioxide (TiO2) thin film growth on silicon substrates using a foundry-scalable atomic layer deposition process with a wide range of doping controls over the Er concentration. Even though the as-grown films are amorphous after oxygen annealing, they exhibit relatively large crystalline grains, and the embedded Er ions exhibit the characteristic optical emission spectrum from anatase TiO2. Critically, this growth and annealing process maintains the low surface roughness required for nanophotonic integration. Finally, we interface Er ensembles with high quality factor Si nanophotonic cavities via evanescent coupling and demonstrate a large Purcell enhancement (≈300) of their optical lifetime. Our findings demonstrate a low-temperature, nondestructive, and substrate-independent process for integrating Er-doped materials with silicon photonics. At high doping densities this platform can enable integrated photonic components such as on-chip amplifiers and lasers, while dilute concentrations can realize single ion quantum memories.

Experimental study on microwave ignition of ADN-based liquid propellant droplets doped with alumina nanoparticles

The objective of this study was to investigate the effects of alumina (Al2O3) nanoparticles on the evaporation, ignition, and combustion of ammonium dinitramide (ADN)-based liquid propellants under microwave irradiation. The alumina nanoparticles were uniformly dispersed in the ADN-based propellant at mass ratios of 25, 50, and 100 ppm, resulting in the formation of nano-fuel. Experimental methods were employed to examine the influence of alumina nanoparticles on the micro-explosion intensity, ignition delay time, combustion duration, critical ignition power, and emission spectra of the nano-fuel droplets. The experimental findings revealed a significant increase in the intensity and frequency of micro-explosion events with the inclusion of alumina nanoparticles. Compared to pure propellant, the nano-fuel with a concentration of 25 ppm exhibited a reduction of 33.5% in ignition delay time and a decrease of 9% in critical ignition power. Furthermore, the emission spectra characteristics of the pure propellant and nano-fuel were analyzed, indicating that alumina nanoparticles notably enhanced the thermal decomposition of ADN and the exothermic reaction of methanol combustion. This study provides an effective approach to improve the evaporation and combustion performance of ADN-based liquid propellants, offering potential possibilities for future applications.

Integrated computational and experimental design of fluorescent heteroatom-functionalised maleimide derivatives.

The bottom-up design and synthesis of organic molecular species with tailored photophysical properties stands as an important challenge to both computational and experimental chemical science. Overcoming this challenge presents the potential to usher in new tools and approaches to improve our ability to develop new technologies, such as molecular sensors and attuned molecular switches. Here, we report the bottom-up design and characterisation of new fluorescent maleimide derivatives using coupled computational and experimental insights. Using an extensive set of experimentally-measured UV/visible spectra for different functionalized maleimides in different solvents, we train an artificial neural network (ANN) to rapidly correlate maleimide structure (and solvent) with emission spectra characteristics. We subsequently use this computational predictor to identify design principles for novel functionalised maleimide structures with targeted photophysical properties; synthesis and characterisation of several new maleimides demonstrates how this combined strategy can offer new directions for tuning photochemistry, for example opening new routes to designing tailor-made fluorescent probes.

Three Ca(II)-Dy(III) heterometallic coordination polymers with different topologies and different water clusters: Synthesis and properties

Three new heterometallic polymers [DyL4Ca2(H2O)2.5(C2H5OH)0.5]·Him·H2O (1), [Dy2L6Ca3(H2O)12]·6H2O (2) and [Dy0.67L2Ca(H2O)2]·4H2O (3) (H2L = 4-chloropyridine-2,6-dicarboxylic acid, im = imidazole) were prepared under solvothermal conditions. The single crystal determination showed that polymers 1 and 3 are two-dimensional structures and polymer 2 is three-dimensional structure. It was found that different types of water clusters were present in these three polymers. They exhibit different topologies with the topological symbols {43}2{46·66·83}, {42·6·123}2{42·6}2 and {63}, where polymer 2 is a new topological type. A series of characterizations, such as XRD, IR, TGA, and solid-state fluorescence, were carried out on these three crystalline materials. They all show characteristic emission spectra of Dy(III) ions. Their quantum yields Фtotal are 4.01% (1), 2.25% (2), 2.88% (3), respectively.

The Covariation of Color and Orange Fluorescence Instabilities in Yellow Sapphires

In recent years, some sapphires were found to fade in sunlight and to increase their color after UV irradiation. This unstable color phenomenon is attributed to the photochromism of corundum. The photochromic effect seriously affects the grading and evaluation of sapphires, although its mechanism is still uncertain. Here, we performed a set of photochromic experiments on sapphire specimens using a 254 nm shortwave UV light source and a D65 light source (which simulates sunlight) to generate different color states exhibiting characteristic absorption, emission, and excitation spectra. We observed that, for different color states, variation in the intensity of the absorption band at ~460 nm was consistent with that of orange fluorescence at 500–800 nm. This observation indicates a relationship between color instability and orange fluorescence. Peaks in excitation spectra at 320, 420, 490, 560, and 637 nm provide insight into the source(s) of excited orange fluorescence, which are related to different types of F-centers and Mg-trapped holes. We propose an explanation for the photochromic phenomenon: the color of photochromic yellow sapphire is the result of a variety of defects that release orange fluorescence simultaneously. Further, we hypothesize that the mechanism of photochromism in yellow sapphires is linked to electron transfer between F-centers and Mg-trapped holes.

Generalization of the Ratiometric Method to Extend pH Range Measurements of the BCECF Probe

There is a variety of fluorescent probes for pH measurements and which are mainly used for biological systems. In general, they can be classified into two groups. The first group includes fluorescent pH probes which exhibit a single fluorescence emission peak. For these probes, the fluorescence excitation profile is pH-dependent and the shape of the emission spectra remains almost constant. Hence, the ratiometric pH measurement-which makes pH determination independent of the probe concentration-is implemented when the excitation is performed at two excitation wavelengths and the fluorescence emission is measured at one wavelength. The second group exhibits a dual fluorescence emission peak. Here, each protonated or deprotonated form exhibits characteristics emission and/or absorption spectra. Shifts between spectra obtained for protonated and deprotonated species can be exploited in order to perform a ratiometric measurement. In this study we present a methodology that evaluates the precision of the ratiometric measurements based on multiple wavelengths excitation to determine the optimum wavelengths combination for pH determination in biological samples. This methodology using the BCECF probe is applied to measure the pH drift in cell culture medium. It exhibits a high precision and significantly extends the range of validity for pH measurements spanning from very acidic to basic.

ACOUSTIC EMISSION SPECTRUM CHARACTERISTICS AND LOCALIZATION EVOLUTION MECHANISM OF COAL AND COAL GANGUE SPECIMEN FAILURE

The mechanical experiments and acoustic emission (AE) experiments of unconfined compression strength (UCS) of coal and coal gangue specimens are carried out to investigate the mechanical characteristics and AE waveform spectrum and localization evolution characteristics of coal and coal gangue specimens. The phase distribution characteristics of the RA-AF values of AE signals are used to characterize the different rupture modes ofcoal and coal gangue specimens. The fast Fourier transform (FFT) method is used to obtain two-dimensional spectral maps of AE signals, extract their main frequencies, and analyze the spectral characteristics of the phase failure of coal specimens. Further, AE signal localization events are selected to study the localization evolution information of coal and coal gangue specimens in the process of phase failure. The experimental results show that the coal gangue specimens have high strength and brittle damage; the largest transverse volume expansion is in the coal specimens, and the coal gangue specimens show the characteristics of high AF and low RA in the 0-0.6<sub>σ f</sub> stage, while the coal specimens show the characteristics of high AF and low RA in the 0-0.4<sub>σ f</sub> stage. The coal gangue specimen, in the initial period of loading, has a small number of AE events, but the AE aggregation phenomenon occurs. The AE events of coal gangue specimens are obviously distributed along the fracture surface and present aggregation in space, while the AE events of coal specimens show a scattered state.

CFSA-AGD: An accurate crosstalk fluorescence spectroscopic decomposition method for identifying and quantifying FDOMs in aquatic environments

Fluorescent substances exist in various aquatic environments and other environmental media. It is a critical task to identify the components accurately and quantify their contents precisely. Based on the Crosstalk Fluorescence Spectroscopy Analysis (CFSA) model, a fluorescence spectroscopic decomposition using the Alternating Gradient Descent (AGD) algorithm is developed. By reducing the residual error of the model through alternating iterations, the CFSA-AGD method achieves unsupervised model training and automatic spectroscopic decomposition without extra experimental operations such as dilution or absorbance measurement, exempting from tedious modeling process. The objectives of this work are to validate that the CFSA-AGD method can comprehensively address the decomposition of fluorescence spectral crosstalk. Furthermore, the novel method is applied to the spectroscopic decomposition of natural FDOMs in aquatic environments as a standard tool. The spectral data analyzing the performance of this method is verified and compared with the conventional methods through the experiment on standard samples. The results indicate that CFSA-AGD has higher spectroscopic decomposition accuracy and gives more abundant information on the characteristic spectra with less residual error than parallel factor analysis. This means that the fluorescence spectra of natural FDOMs can be decomposed into the characteristic fluorescence emission spectra of single components with higher accuracy and the characteristic fluorescence absorption spectra that cannot be obtained by the conventional methods. Meanwhile, it improves the analytical precision of the contents (from R2 ≥ 0.9778 to R2 ≥ 0.9920) and reduces the ultimate residual error by two orders of magnitude (from 1.42 × 10−1 to 4.68 × 10−3) when the method is used to estimate the measured fluorescence spectra.

Rare Earth Complexes of Europium(II) and Substituted Bis(pyrazolyl)borates with High Photoluminescence Efficiency.

Rare earth europium(II) complexes based on d-f transition luminescence have characteristics of broad emission spectra, tunable emission colors and short excited state lifetimes, showing great potential in display, lighting and other fields. In this work, four complexes of Eu(II) and bis(pyrazolyl)borate ligands, where pyrazolyl stands for pyrazolyl, 3-methylpyrazolyl, 3,5-dimethylpyrazolyl or 3-trifluoromethylpyrazole, were designed and synthesized. Due to the varied steric hindrance of the ligands, different numbers of solvent molecules (tetrahydrofuran) are participated to saturate the coordination structure. These complexes showed blue-green to yellow emissions with maximum wavelength in the range of 490-560 nm, and short excited state lifetimes of 30-540 ns. Among them, the highest photoluminescence quantum yield can reach 100%. In addition, when the complexes were heated under vacuum or nitrogen atmosphere, they finally transformed into the complexes of Eu(II) and corresponding tri(pyrazolyl)borate ligands and sublimated away.

Magnetic and photoluminescence properties of rare-earth substituted quaternary spinel ferrite nanoparticles

Rare earth substituted quaternary spinel ferrites Ni0.5Zn0.5Fe1.95Eu0.05O4, Co0.5Zn0.5Fe1.95Dy0.05O4, and Cu0.5Zn0.5Fe1.95Tb0.05O4 were prepared by a low-temperature co-precipitation method without any post heat treatment. Structural confirmation of the prepared materials was done by XRD. Using TEM, their morphology was investigated. Magnetic studies were conducted using VSM. The prepared materials exhibit soft ferrimagnetic nature. The magnetization curves were further studied by applying the law of approach to saturation. Downconversion and upconversion photoluminescence properties of the prepared materials were investigated at different excitation wavelengths. No characteristic emission spectra of the rare-earths elements were observed. In the case of downconversion, a broad emission band formed by sub-bands and in the upconversion spectra, characteristic emission peaks were observed in all compositions. The observed emission spectra depict the presence of multiple energy levels within the band gap of spinel ferrites.