Emission Band Research Articles

Preparation and Performance of a Fiber Optic Temperature Sensor with Multiple Fluorescence Mechanisms.

The tip of a piece of plastic fiber was dyed with thymol blue to form a temperature probe. The fiber optic sensor was calibrated on a heatboard by comparison with a K-type thermal couple. Fluorescence characteristics including fluorescence intensity, emission bandwidth, peak & barycenter wavelengths, and self-referenced intensity ratio were used to carry the information of environment temperature. Accordingly, more than five temperature sensing functions were retrieved from the fluorescent sensor. Among such functions, the emission band barycenter showed premium precision. Temperature-driven shift of the emission band barycenter has a sensitivity of 0.095nm/K, with a nonlinearity of 2.2%FS, resolution of 4K and repeatability of 1.8%FS. The sensor can find its applications in wearable devices and radiofrequency ablation. Finally in a verification experiment, the sensor was used to monitor the temperature of a microwave oven chamber in real time.

Controlling the Orientation-Dependent Second Harmonic Generation in Hybrid Germanium Perovskite Crystals.

Manipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface-dependent anisotropic SHG with the precise design of (101) and (20) MAGeI3 facets. Based on the SHG measurement, the (101) MAGeI3 single crystal exhibits larger SHG (1.3 × (20) MAGeI3). Kelvin probe force microscopy imaging shows a smaller work function for the (101) MAGeI3 compared with the (20), which indirectly demonstrates the stronger intrinsic polarization on the (101) surface. X-ray photoelectron spectroscopy confirms the band bending within the (101) facet. Temperature-dependent steady-state and time-resolved photoluminescence spectroscopy show shorter lifetime and wider emission band in the (101) MAGeI3 single crystal, revealing the higher defect states. Additionally, powder X-ray diffraction patterns show the (101) MAGeI3 possesses larger in-plane polar units [GeI3]- density, which could directly enhance the spontaneous polarization in the (101) facet. Density functional theory (DFT) calculation further demonstrates the higher intrinsic polarization in the (101) facet compared with the (20) facet, and the larger built-in electric field in the (101) facet facilitates surface vacancy defect accumulation. Our work provides a new angle in tuning and optimizing hybrid perovskite-based nonlinear optical materials.

Embedding Te4+ into Sn4+-Based Metal Halide To Passivate Structure Defects for High-Performance Light-Emitting Application.

Low-dimensional lead-halide hybrids are an emerging class of optical functional material but suffer the problems of toxicity and poor air stability. Among lead-free metal halides, tin(IV)-based metal halides are promising optoelectronic materials due to their robust structure and environmental friendliness. However, their photoluminescence (PL) properties are poor, and the underlying mechanisms are still elusive. Herein, a stable Sn4+-based halide hybrid, (C4H7N2)2SnCl6, was developed, which however exhibits poor PL properties at room temperature (RT) due to the lattice defects and the robust crystal structure. To enhance its PL efficiency, the Te4+ ion with a stereoactive 5s2 lone pair has been introduced into the lattice. As a result, Te4+-doped (C4H7N2)2SnCl6 displays broadband orange emission (∼640 nm) with a PL efficiency of ∼46% at RT. Interestingly, Te4+-doped (C4H7N2)2SnCl6 shows triple emission bands at 80 K, which could be due to the synergistic effect of the organic cations and the self-trapped state induced by Te4+. Additionally, high-performance white light-emitting diodes were prepared using Te4+-doped (C4H7N2)2SnCl6, revealing the potential of this material for lighting applications. This study provides new insight into the PL mechanism of Sn4+-based metal-halide hybrids and thus facilitates the design and development of eco-friendly light-emitting metal halides.

Exploring the scaling factors for infrared modes of PANHs - A case study on cationic 3-Azafluoranthene.+ and protonated 3-Azafluoranthene.

Infrared (IR) emission bands by interstellar Polycyclic Aromatic Hydrocarbons (PAHs) and Polycyclic Aromatic Nitrogen Heterocycles (PANHs) are observed towards a large variety of interstellar objects and offer detailed insights into the chemistry and physics of the interstellar medium. The analysis of the emission bands, and thus the interpretation of the molecular characteristics of the carriers, heavily relies on the use of density functional theory (DFT) calculated IR spectra. However, there are significant challenges in accurately predicting the experimental IR band positions, particularly for PANH emission vibrational modes around 6 mm. In this work, we present gas-phase mid-infrared (mid-IR) spectra of cationic 3-azafluoranthene (3AF.+) and protonated 3-azafluoranthene (3AFH+) to investigate their experimental IR band positions in relation to DFT calculated bands. The experimental spectra are compared to DFT simulated spectra, where different approaches were followed to correct for anharmonicities. The best agreement is achieved by scaling frequencies of modes with large nitrogen displacements with a different factor. Even though our findings might be limited to a small number of PANH structures, they indicate, that nitrogen atom incorporation needs to be accounted for by carefully adjusting the corresponding scaling factors while computing IR spectra of PANHs on DFT level.

Far-red emitting Li2TiO3: Cr3+ phosphor: Synthesis, luminescence properties and potential applications

The Cr[Formula: see text]-activated phosphor can emit far-red light under the excitation of an external light source, mainly due to the transition of the outermost electrons of Cr[Formula: see text] from the 2E level to the 4A2 level in a strong crystal field environment. A novel far-red Li2TiO3: Cr[Formula: see text] phosphor was prepared by the solid-state method. Under the excitation of 356[Formula: see text]nm, the Li2TiO3: Cr[Formula: see text] phosphors emit intense far-red light in 600–850[Formula: see text]nm with a central wavelength of 732[Formula: see text]nm. The emission band of all samples was matched with the absorption bands of phytochrome P[Formula: see text]. The experimental data and theoretical calculation confirmed that Cr[Formula: see text] is surrounded by a strong crystal field environment. The effect of Cr[Formula: see text] doping concentration on the luminescence intensity was analyzed. These research works demonstrate that far-red Li2TiO3: Cr[Formula: see text] phosphors have potential applications in plant growth lights.

Synthesis of phosphorus/arsenic tridentate ligands and their application for luminescent copper(I) halide complexes

We synthesized arsenic analogs of a tridentate PPP ligand, bis[2‐(diphenylphosphino)phenyl]phenylphosphine, achieving yields of 40% to 71%. Additionally, we prepared copper(I) halide (CuX, X = Br, I) complexes with these ligands, with yields between 43% and 84%. Using both experimental and computational methods, we examined their structures and photophysical characteristics. Single crystal X‐ray diffraction showed that all eight complexes had distorted tetrahedral geometries. These complexes exhibited photoluminescence with emission bands peaking from 506 nm to 551 nm and quantum yields up to 0.92 at room temperature. Emission lifetimes varied and showed no direct correlation with quantum yields or wavelengths. Physical manipulation and solvent variations significantly altered their photoluminescent properties. DFT and TD‐DFT calculations revealed that higher arsenic content increased spin‐orbit coupling constants, with iodide complexes performing better than bromide ones due to heavier elements enhancing spin‐orbit coupling. Substituting phosphorus with arsenic significantly affected the luminescence quantum yield and lifetime, demonstrating the heavy‐atom effect of arsenic. The position of arsenic in the ligands critically influenced the photophysical outcomes of the CuX complexes.

Infrared Spectrum of the Pyrene Anion in the CH Stretching Region.

In this work, we report the infrared spectrum of the pyrene anion, measured using messenger tagging with up to three Ar atoms. We assign the spectrum using density functional theory and vibrational perturbation theory. We discuss our results in the context of computed and experimental spectra from the literature as well as recent observations from astronomical sources, addressing the question of whether polycyclic aromatic hydrocarbon anions could contribute to the strong infrared emission bands at 3.29 μm from carbon-rich regions of space.

Brilliant quantum dots’ photoluminescence from a dual-resonance plasmonic grating

Semiconductor quantum dots (QDs) have recently caused a stir as a promising and powerful lighting material applied in real-time fluorescence detection, display, and imaging. Photonic nanostructures are well suited for enhancing photoluminescence (PL) due to their ability to tailor the electromagnetic field, which raises both radiative and nonradiative decay rate of QDs nearby. However, several proposed structures with a complicated manufacturing process or low PL enhancement hinder their application and commercialization. Here, we present two kinds of dual-resonance gratings to effectively improve PL enhancement and propose a facile fabrication method based on holographic lithography. A maximum of 220-fold PL enhancement from CdSe/CdS/ZnS QDs are realized on 1D Al-coated photoresist (PR) gratings, where dual resonance bands are excited to simultaneously overlap the absorption and emission bands of QDs, much larger than those of some reported structures. Giant PL enhancement realized by cost-effective method further suggests the potential of better developing the nanostructure to QD-based optical and optoelectronic devices.

Luminescence of CsLa1-хCeхSiS4 thiosilicate solid solution: From STE to Ce3+ emission

A series of single crystals of CsLa1-хСехSiS4 monophasic solid solution (x = 0–1) has been obtained for the first time by high-temperature flux synthesis. Methods of XRD and chemical analysis, absorption and low-temperature (from T = 5 K) luminescent spectroscopy were used. The results of the band scheme calculating using density functional theory correlate with spectroscopy data. One non-elementary d → f emission band of Ce3+ ions is observed in the region of 520 nm in the luminescence spectra at room temperature at any value of the x parameter. The luminescence decay kinetics of Ce3+ ions upon excitation by a pulsed electron beam, X-ray synchrotron radiation or intracenter photoexcitation is characterized by a nanosecond component. As the parameter x increases, the decay time is reduced from 132 ns (x = 0.005) to 0.88 ns (x = 1). The luminescence decay kinetics upon photoexcitation at x = 0.005–0.12 is characterized by monoexponential decay with τ = 31.4 ± 0.2 ns. Concentration quenching of the Ce3+ ion photoluminescence is not observed up to the value of the parameter x = 0.12; it only appears at x = 1. The anomalously short decay time of the Ce3+ ions luminescence in CsCeSiS4 upon both X-ray excitation and photoexcitation is associated with concentration quenching.At temperature 5 K, new intense bands at 408 and 688 nm in addition to the Ce3+ emission band observed in the photoluminescence spectra of nominally pure CsLaSiS4 or at the lowest parameter value x = 0.005. These bands correspond to the luminescence of self-trapped excitons (STE) and defects. With increasing x parameter, the STE emission band is reabsorbed by the absorption of Ce3+ ions and is quenched due to the resonance energy transfer STE → Ce3+ center. Thermoluminescence glow curves of CsLa1-xCexSiS4 irradiated with X-ray at T = 90 K are characterized by several low temperature intense peaks, which indicates a high concentration of charge carrier traps.

Luminescence Dynamics of BaAl2O4:Eu2+ Phosphor.

We studied steady-state and time-resolved photoluminescence of Eu doped BaAl2O4 phosphor. The undoped BaAl2O4 sample shows a dominant blue emission band at ~ 428nm and two secondary maxima at ~ 405 and 456nm due to F-centre and aggregate defects such as F2 -centre. The samples after doping of Eu at 1-5% show additional emission bands at ~ 485 and 518 nm due to Eu2+ centre and a red emission band at ~ 657nm is attributed to Eu3+ centre. The sample doped with 2% of Eu shows anomalous emission having the dominant peak at ~ 494nm. The average luminescence lifetime of the emission band at ~ 428nm in the undoped sample was estimated to be (3.29 ± 0.91) ns. The average luminescence lifetime of this emission band after doping of Eu was found to increase by 102 orders of magnitude. The intensity of the 428nm blue emission band was found to quench after doping of Eu beyond 3%. The concentration quenching effect was attributed to dipole-quadrupole interaction. Further, a non-radiative fluorescence energy transfer mechanism from an extrinsic Eu2+ centre to an intrinsic F-centre is proposed to describe the luminescence dynamics of the samples.

A highly selective dual-signal response ratiometric fluorescence sensing strategy for malachite green in fish based on carbon dots/copper nanoclusters nanocomposite

Malachite green (MG), a widely used antiparasitic agent, poses health risks to human due to its genotoxic and carcinogenic properties. Herein, a stable dual-emission fluoroprobe of carbon dots/copper nanoclusters is prepared for highly selective detection of MG based on the inner filter effect. This probe exhibits characteristic emission bands at 435 and 625 nm when excited at 376 nm. After adding MG, the both emission signals were significantly quenched, and the ratio of fluorescence intensity (F435/F625) was linearly related to the concentration of MG in the range of 0.05–40 μmol L−1 with a limit of detection of 18.2 nmol L−1. Meanwhile, the two signals exhibit linear relationships with the concentration of MG, respectively, and the corresponding detection results were consistent. The fluoroprobe was successfully used for the detection of MG in fish samples with the recoveries ranging from 96.0% to 103.8% and a relative standard deviation of <3.3%.

Emission Spectra of Uranium Particulates at High Temperature.

The emission spectrum of micron-scale uranium particulates at high temperatures in the ultraviolet, visible, and near-infrared spectral regions is investigated using a heterogeneous shock tube. Temperatures from 3000 to 9000 K are characterized in an inert argon environment and with incremental amounts of added oxygen. Atomic line spectra do not emerge above the continuum emission spectrum until between 4500 and 5000 K in pure argon, and 6100 and 6600 K in 1% oxygen. For 5% oxygen, however, the threshold for atomic emission drops below 3800 K. Uranium monoxide molecular emission in the strongest visible band at 595.4 nm is not observed at any condition. Uncertainties in particle temperature determination in high-temperature shock tube environments are discussed, and limitations to such measurements are presented, such as those from experimental factors such as the powder loading method and expected detection limits of uranium species in relevant conditions.

Rare-Earth-Ion (RE3+)-Doped Aluminum and Lanthanum Borates for Mobile-Phone-Interrogated Luminescent Markers

In this paper, we present the synthesis and luminescent spectra of rare-earth (RE)-doped aluminum and lanthanum borates intended to serve as narrow excitation–emission band fluorescent markers. We perform a detailed 3D excitation–emission matrix (EEM) analysis of their spectra, compare the measurements from both standard and mobile phone spectrometers, and outline the basic differences and advantages of each method. While smartphones have a different and non-uniform spectral response compared to standard spectrometers, it is shown that they offer a number of advantages such as contactless interrogation, efficient suppression of the UV excitation light, and simultaneous spectral analysis of spatially arranged arrays of fluorescent markers. The basic emission peaks have been observed and their corresponding electronic transitions identified. The obtained results show that the rare-earth-doped La and Al borates feature excitation–emission bandwidths as low 15 nm/12 nm, which makes them particularly appropriate for use as luminescent markers with UV LED excitation and smartphone interrogation.

Crystal growth, physical and optical properties of TlSr2Cl5 and TlSr2Br5

Small diameter (Ø 16 mm) TlSr2Cl5 and TlSr2Br5 crystals were grown by the Vertical Bridgman method. X-ray diffraction measurements show that both have the monoclinic crystal structure with space group P21/c. TlSr2Cl5 and TlSr2Br5 have a density of 4.14 g/cm3 and 5.03 g/cm3, respectively. The effective Z of TlSr2Cl5 and TlSr2Br5 is 63.7 and 58.6, respectively. Radioluminescence spectra of TlSr2Cl5 and TlSr2Br5 feature a broad emission band peaking at 440 and 445 nm, respectively. The light yield of TlSr2Cl5 and TlSr2Br5 was estimated to be 17,000 and 45,000 ph/MeV, respectively.

Yb3+ concentration influence on NIR and upconversion emission and temperature sensing properties of Er3+/Yb3+ co-doped Ta2O5 particles

We synthesized Er3+ and Yb3+ co-doped tantalum oxide (Ta2O5) spherical sub-micrometric particles by a facile method involving formation of tantalum glycolates after pouring in acetone. Then, we investigated how the annealing temperature and Yb3+ concentration (0–30 mol %) affect their structural and luminescence properties. Particle sizes ranged from 146 to 258 nm for the samples annealed at 800 °C. XRD analysis revealed the orthorhombic L-Ta2O5 crystalline structure. The different symmetry sites that the rare earth ions can occupy within the Ta2O5 structure led to intense and broad emission bands centered around 1530 nm. Up-conversion measurements and the calculated number of photons for intense green and red emissions obtained with 980 and 1550 nm excitations helped us to elucidate the mechanisms involved at both excitation wavelengths. We investigated how the 0.5 mol % Er3+/1.5 mol % Yb3+ co-doped Ta2O5 sample performs as a primary thermometer by using the Boltzmann distribution law to predict the absolute temperature from the ratio between the Er3+ 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions. We obtained a maximum relative thermal sensitivity of 0.97 ± 0.04 % K−1 and a minimum δT of 2.41 K. The calculated repeatability was above 95%. These results show that promising nanothermometer based on Ta2O5 with controlled size and morphology can be designed.

Printable Light-Emitting Metasurfaces with Enhanced Directional Photoluminescence.

Nanoimprint lithography is gaining popularity as a cost-efficient way to reproduce nanostructures in large quantities. Recent advances in nanoimprinting lithography using high-index nanoparticles have demonstrated replication of photonic devices, but it is difficult to confer special properties on nanostructures beyond general metasurfaces. Here, we introduce a novel method for fabricating light-emitting metasurfaces using nanoimprinting lithography. By utilizing quantum dots embedded in resin, we successfully imprint dielectric metasurfaces that function simultaneously as both emitters and resonators. This approach to incorporating quantum dots into metasurfaces demonstrates an improvement in photoluminescence characteristics compared to the situation where quantum dots and metasurfaces are independently incorporated. Design of the metasurface is specifically tailored to support photonic modes within the emission band of quantum dots with a large enhancement of photoluminescence. This study indicates that nanoimprinting lithography has the capability to construct nanostructures using functionalized nanoparticles and could be used in various fields of nanophotonic applications.

Exploring innovative applications of Sr2MgSi2O7:Fe3+ luminescent system in surface-triggered fingerprint divergence and cheiloscopy screening

In this study, we employ a cost-effective combustion method to synthesize (1–11 mol %) Fe3+ doped Sr2MgSi2O7 nanophosphors (SMSO NPs) and conduct a comprehensive investigation into their structural and luminescent properties. The impact of iron concentration on the structural and optical characteristics is thoroughly analysed, revealing a tetragonal crystal structure with space group P-421m through Rietveld refinement and X-ray Diffraction (XRD) patterns. Scanning electron microscopy showcases the random dispersion of agglomerated particles with non-uniform dimensionality. Energy Dispersive X-ray analysis (EDS) assesses the nominal composition of Sr, Mg, Si, Fe, and O, while X-ray Photon Spectroscopy (XPS) confirms the direct incorporation of Fe3+ ions into the SMSO lattice. Photoluminescence (PL) emission spectra exhibit a deep red emission band at 718 nm. The residual luminescence intensity of SMSO:7Fe3+ at 200 °C is 91 %. Under 365 nm UV light, the optimized SMSO:7Fe3+ NPs displays easily identifiable levels I-III fingerprints (FPs) features with good resolution and contrast. The resilient luminescence and nano-regime of the phosphor reveal well-defined type I–V groove patterns in latent lip prints (LLPs) on various non-porous surfaces, unaffected by background interference or colour distraction. This study highlights SMSO:7Fe3+ NPs as a promising option for individualizing and detecting latent fingerprints (LFPs) and lip prints (LPs).

Evaluating the biomolecular interaction between delamanid/formulations and human serum albumin by fluorescence, CD spectroscopy and SPR: Effects on protein conformation, kinetic and thermodynamic parameters

Delamanid is an anti-tuberculosis drug used for the treatment of drug-resistant tuberculosis. Since delamanid has a high protein bound potential, even patients with low albumin levels should experience high and rapid delamanid clearance. However, the interaction between delamanid and albumin should be better controlled to optimize drug efficacy. This study was designed to evaluate the binding characteristics of delamanid to human serum albumin (HSA) using various methods: fluorescence spectroscopy, circular dichroism (CD), surface plasmon resonance (SPR), and molecular docking simulation. The fluorescence emission band without any shift indicated the interaction was not affected by the polarity of the fluorophore microenvironment. The reduction of fluorescence intensity at 344nm was proportional to the increment of delamanid concentration as a fluorescence quencher. UV-absorbance measurement at the maximum wavelength (λmax, 280nm) was evaluated using inner filter effect correction. The HSA conformation change was explained by the intermolecular energy transfer between delamanid and HSA during complex formation. The study, which was conducted at temperatures of 298K, 303K, and 310K, revealed a static quenching mechanism that correlated with a decreased of bimolecular quenching rate constant (kq) and binding constant (Ka) at increased temperatures. The Ka was 1.75–3.16 × 104M−1 with a specific binding site with stoichiometry 1:1. The negative enthalpy change, negative entropy change, and negative Gibbs free energy change demonstrated an exothermic-spontaneous reaction while van der Waals forces and hydrogen bonds played a vital role in the binding. The molecular displacement approach and molecular docking confirmed that the binding occurred mainly in subdomain IIA, which is a hydrophobic pocket of has, with a theoretical binding free energy of −9.33kcal/mol. SPR exhibited a real time negative sensorgram that resulted from deviation of the reflex angle due to ligand delamanid-HSA complex forming. The binding occurred spontaneously after delamanid was presented to the HSA surface. The SPR mathematical fitting model revealed that the association rate constant (kon) was 2.62 × 108s−1M−1 and the dissociation rate constant (koff) was 5.65 × 10−3 s−1M−1. The complexes were performed with an association constant (KA) of 4.64 × 1010 M−1 and the dissociation constant (KD) of 2.15 × 10−11 M. The binding constant indicated high binding affinity and high stability of the complex in an equilibrium. Modified CD spectra revealed that conformation of the HSA structure was altered by the presence of delamanid during preparation of the proliposomes that led to the reduction of secondary structure stabilization. This was indicated by the percentage decrease of α-helix. These findings are beneficial to understanding delamanid-HSA binding characteristics as well as the drug administration regimen.

Development of gum Arabic/chitosan-infiltrated photoluminescent wooden smart window with multifunctional properties

Photochromic wood materials are very important and appealing for smart windows. Herein, we describe the development of transparent photochromic wood that can change its color under ultraviolet and visible lights. Photoluminescent transparent wood was prepared by delignification of wood followed by infiltration with a combination of gum Arabic/chitosan/acrylic acid (ACA), lanthanide-activated aluminum strontium oxide (LASO) as a photoluminescent, and Genipin as a cross-linking agent. The produced mixture was then infused into the lignin-modified wood substrate. In order to develop a luminescent colorless wood, the LASO phosphor must be well-distributed in the ACA solution without aggregation. According to the colorimetric parameters and photoluminescence spectra, this optically active wooden window switched color from transparent in daylight to green when UV-irradiated. Transmission electron microscopy (TEM) was employed to examine the morphological features of phosphor nanoparticles. The morphological features of the developed smart wooden window were investigated by scanning electron microscopy (SEM), X-ray fluorescent spectroscopy (XRF), and energy-dispersive X-ray analyzer (EDX). The mechanical performance was explored by investigating both hardness and resistance to scratches. The luminescent woods displayed an emission band at 518 nm when excited at 365 nm. The superhydrophobic performance and ultraviolet shielding of woods were improved upon increasing the phosphor content.

An experimental and theoretical study on mechanistic insights into urolithin-based ratiometric fluorescent probe for instant quantitative detection of fluoride ions

Fluoride detection has been playing an important role in chemical, biological, and medicinal field, especially for keeping physical health and resisting environmental pollution. Herein, a urolithin B fluorescent probe has been successfully developed with good sensitivity, selectivity, anti-interference ability. The low limit of detection (LOD) refers to 0.156 μM, and the instant response time to F− is less than 1 s. The probe is suitable for quantitatively and qualitatively ratiometric detection for F− in solution with two distinct emission bands at 425 (blue) and 566 nm (orange), with the coordinate change of CIE from (0.38, 0.41) to (0.22, 0.11). Urolithin B displayed a remarkable ratiometric fluorescence response towards F−. The detection mechanistic was further proposed by NMR and electronic spectroscopic experiments combining with time-dependent density functional theoretical calculation.