Emission Band Shape Research Articles

Knotted or unknotted? A theoretical quantum protocol for luminescence simulation of metallo-supramolecular knots

Entangled structures are topological architectures often observed not only in the macroscopic world, but also at the molecular level with many examples in biological systems (DNA, RNA). In recent decades, these fascinating entities have aroused considerable interest among chemists with the advent of metallo-supramolecular knots. Notwithstanding the burgeoning of such metal complexes in literature, their use as luminescent emitters as well as systematic studies on their luminescence properties are still extremely limited. In view of this, a theoretical DFT protocol dedicated to luminescence profile simulations of these peculiar “entwined” species is highly desirable. In this work, we propose a robust and affordable DFT computational workflow able to recreate meticulously the emission band-shape of different metallo-supramolecular knots. As a result of a preparatory DFT benchmark, we decided to use HSEH1PBE/LanL2DZ level via Born-Oppenheimer molecular dynamics to explore the change in the coordination environment around the metal centers in the excited state (S1). Thereupon, a detailed recruiting of TD-DFT functionals recommended the mPW3PBE/LanL2DZ level as the most precise and transferable method to model accurately metallo-supramolecular knots emission spectra as metal ions, internal spacers and interlocking modes vary.

Fluorescence saturation imaging microscopy: molecular fingerprinting in living cells using two-photon absorption cross section as a contrast mechanism.

Imaging of molecular-specific photophysical parameters such as fluorescence intensity, emission band shape, or fluorescence decay is widely used in biophysics. Here we propose a method for quantitative mapping of another molecular-specific parameter in living cells, two-photon absorption cross section, based on the fluorescence saturation effect. Using model dye solutions and cell culture, we show that the analysis of the fluorescence signal dependencies on the intensity of two-photon excitation within the range typical for routine two-photon microscopy experiments allows one to reconstruct two-photon absorption cross section maps across the sample. We believe that the absorption cross section contrast visualized by the proposed fluorescence saturation imaging microscopy could be a new tool for studying processes in living cells and tissues.

Role of the Rigid Host Structure in Narrow-Band Green Emission of Eu2+ in Rb2Na2(Li3SiO4)4: Insights into Electron-Phonon Coupling.

Eu2+-activated alkali-lithosilicate phosphors exhibit narrow-band emissions that are attractive to high color-rendition and wide color-gamut displays. The microscopic mechanism behind the small emission bandwidth is not presently understood. Here, we report an explicit calculation of the vibronic process occurring in the narrow-band green emission of Rb2Na2[Li3SiO4]4:Eu2+. We show that due to the high rigidity of the host material, the structural strain induced by the localized Eu2+ 4f-5d excitation is distributed among the atoms far beyond the first coordination shell and hence reduces the local structural relaxation around Eu2+. The emission bandshape is thus mainly controlled by the coupling of the electronic transition with the phonon modes associated with motions of host constituent atoms, which was further validated by the good agreement of the calculated bandshape with the experiment. The results provide insights into the generation of narrow-band emission and improve our knowledge on electron-phonon coupling of 4f-5d transitions in phosphors.

A three-component copper phosphonate complex as a sensor platform for sensitive Cd2+ and Zn2+ ion detection in water via fluorescence enhancement

A three-component molecular copper phosphonate [Cu2(H4tpmm)2(Hpybim)2]·H2O (1·H2O), where H6tpmm ​= ​2,4,6-tris(phosphorylmethyl)mesitylene and Hpybim ​= ​2-(2-pyridyl)benzimidazole, showing high thermal stability up to approximately 370 ​°C has been prepared. Complex 1·H2O has a dinuclear structure symmetry-related by a crystallographic inversion center, in which the Cu(II) center suits a highly distorted square pyramidal geometry. Complex 1·H2O shows two extremely weak emission bands in both solid state and H2O suspension phase. However, as Cd2+ and Zn2+ were added into the H2O suspension of 1·H2O, the fluorescence intensity would be remarkably enhanced by 11.1 and 25.2 times, respectively, with a dramatic change in the emission band shape. The fluorescence enhancement sensing of 1·H2O toward Cd2+ and Zn2+ in H2O is highly sensitive with limit of detection (LOD) values of 1.35 and 0.89 ​μM, respectively. Such sensing performances are negligibly interfered by most perturbed metal ions but largely affected by Fe3+, Ni2+, and Co2+. EDX and XPS analyses show the occurrence of weak binding interactions between the Cd2+/Zn2+ ions and the structure of 1·H2O, resulting in fluorescence enhancement. This work demonstrates a highly water stable molecular copper phosphonate behaving as a sensor platform suitable for Cd2+ and Zn2+ ion detection in water via remarkable fluorescence enhancement, providing a new method for metal phosphonate complexes.

Ratiometric Detection of Mercury (II) Ions in Living Cells Using Fluorescent Probe Based on Bis(styryl) Dye and Azadithia-15-Crown-5 Ether Receptor.

Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg2+ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500–600 nm) to red (600–730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg2+ concentration in the 37 nM–1 μM range.

Soft X-ray Li-K and Si-L2, 3 Emission from Crystalline and Amorphous Lithium Silicides in Lithium-Ion Batteries Anode

Soft X-ray Li-K and Si-L2, 3 emission spectra of crystalline and amorphous lithium silicides Li13Si4 and Li15Si4 forming upon electrochemical lithiation of silicon anode in lithium-ion batteries (LIBs) have been investigated theoretically. It is shown that shape and energy position of X-ray emission bands can be used for determination of the chemical structure and composition of the electrochemically lithiated silicon, while the intensities of Li-K and Si-L2, 3 bands provide information on Li concentration. It is demonstrated that theoretical methods of soft X-ray emission spectroscopy (XES) can be used as a powerful tool for the detailed analysis of the electronic and structural properties of Li-Si alloys in LIBs.

UV Photolysis of Pyrazine and the Production of Hydrogen Isocyanide.

Photolysis of the diazine heterocycle, pyrazine, following irradiation at 308, 248, and 193 nm was examined using nanosecond time-resolved Fourier transform infrared emission spectroscopy. The resulting time-resolved IR emission spectra reveal that for 308 and 248 nm vibrationally highly excited pyrazine is produced, but no photolysis products were detected. However, at 193 nm excitation, the measured IR emission spectra consist solely of resonances originating from rovibrationally excited photofragments, including acetylene (HCCH), hydrogen cyanide (HCN), and hydrogen isocyanide (HNC), indicating that photofragmentation proceeds from vibrationally highly excited pyrazine on the ground electronic state. Spectral fit analysis of the time-resolved HCN and HNC IR emission band shapes and intensities allowed an estimate of the nascent product population distributions, from which a lower bound estimate of the HNC/HCN branching ratio was deduced as Φ ≥ 0.07. Additionally, ab initio calculations were performed in order to examine the propensity of photoinduced reactions on the ground- and lowest-energy excited-state surfaces. The calculations provide a basis for understanding the wavelength dependence of the UV photolysis of pyrazine, the photolytic production of HNC, and also explain previous experimental observations in the literature.

Effect of H2O and D2O Thermal Anomalies on the Luminescence of Eu3+ Aqueous Complexes

Aqueous solutions of luminescent metal–ion complexes, in particular, those of lanthanide ions, can play an essential role in biomedical applications. For all of these applications, the knowledge about the influence of temperature variations within the physiological range (20–60 °C) on their optical properties becomes essential. At variance with other liquids, water is unique as it does present an anomalous temperature-dependent behavior. In particular, most water properties present remarkable physicochemical changes above a certain temperature, which ranges between 30 and 50 °C. In this work, we systematically investigate the effect of temperature on the luminescence properties of Eu3+ ions when dissolved in either H2O or D2O. An anomalous thermal behavior, manifested as a bilinear trend, with crossover at around 35 °C for H2O and 38 °C for D2O, is found in a variety of Eu3+ optical spectroscopic properties (branching ratio, luminescence lifetime, and emission band shape). The observed changes are tentatively explained here in terms of different aggregation states of H2O and D2O molecules below and above the crossover temperature. Such changes in the molecular clustering lead to a temperature-induced change in the relative concentrations of the 8-fold and 9-fold coordinated Eu3+ complexes. Finally, we have observed that the pH of the aqueous solution plays an essential role in defining the temperature at which the anomaly takes place so that the differences in the values reported in the literature for the crossover temperature are accounted for.

Fabrication and luminescence properties of U:YAG transparent ceramic

Uranium doped yttrium aluminum garnet (YAG) transparent ceramic with Ca2+ as charge compensator and sintering aid was firstly fabricated by vacuum sintering technique using the co-precipitation synthesis of raw powders. The structural, optical spectral and luminescence properties of the U:YAG ceramic have been investigated in detail. The experimental results show that uranium doped in YAG matrix has not changed the crystal structure. Vacuum sintering 15 h in 1800 °C, the sample has a pore-free structure with an average grain size of about 3.5 μm, and in-line transmittance reaches up to 78% in the visible wavelength region. The excitation spectrum showed a sharp band around 458 nm, and the emission spectrum revealed the intense green emission located at 520 nm. Further, with respect to the shape of emission band and luminescence color, uranium was inferred to exist as uranate ion (UO66−) in the YAG host where it replaces the ‘Y’ ions at dodecahedral site with surrounding defect centers created for charge compensation.

Molecular ND Band Spectroscopy in the Divertor Region of Nitrogen Seeded JET Discharges

In this contribution we present OES measurements in the JET tokamak of the deuterated NH (ND) radical and the correlation between results of those experiments and measurement of ammonia production. The observation region covers most of the divertor and its outer throat. Measurements are performed in different magnetic configurations. The results include temporal and spatial dependence of the molecular emission intensity and study of the emission band shape (vibrational and rotational temperatures) during different JET pulses, with or without nitrogen seeding. Results are a step towards the understanding of nitrogen-containing molecule creation and destruction in the divertor plasma.

Time-resolved optical diagnostics of solution plasma formed with graphite electrodes

The glow discharge plasma formed by the application of pulsed high voltage in solution (solution plasma, SP) is expected as a novel reaction field for syntheses of carbon nanomaterials, where temperature control crucially affects the structures of the resultant materials. In the present study, the temperatures of reaction intermediates for carbon material syntheses in SP with graphite electrodes were elucidated by time-resolved optical emission spectroscopy. By comparing the emission bandshapes from C2 and CH radicals with the simulated ones, the temporally averaged temperatures of the radicals were successfully estimated as 3,000 to 6,000 K. From the temporal evolution of the radical temperature, the temperature was almost kept in the range between 2,500 and 4,000 K, except for sudden elevations to more than 7,000 K with durations of less than 0.1 µs. The temperatures were observed to be markedly lower than those in arc discharge plasma, which is conventionally applied to carbon nanomaterial syntheses. It is suggested that SP should provide a reaction field in which the sp2 bonds between carbon atoms in the product nanomaterials are less dissociated than the arc discharge plasma.

Is Photolytic Production a Viable Source of HCN and HNC in Astrophysical Environments? A Laboratory-based Feasibility Study of Methyl Cyanoformate

Motivated by the possibility that cyano-containing hydrocarbons may act as photolytic sources for HCN and HNC in astrophysical environments, we conducted a combined experimental and theoretical investigation of the 193 nm photolysis of the cyano-ester, methyl cyanoformate (MCF). Experimentally, nanosecond time-resolved infrared emission spectroscopy was used to detect the emission from nascent products generated in the photolysis reaction. The time-resolved spectra were analyzed using a recently developed spectral reconstruction analysis, which revealed spectral bands assignable to HCN and HNC. Fitting of the emission band shape and intensity allowed determination of the photolysis quantum yields of HCN, HNC, and CN (A22 Π1)and an HNC/HCN ratio of ∼0.076 ± 0.059. Additionally, multiconfiguration self-consistent field calculations were used to characterize photoexcitation-induced reactions in the ground and four lowest singlet excited states of MCF. At 193 nm excitation, dissociation is predicted to occur predominantly on the repulsive S 2 state, with minor pathways via internal conversion from S 2 to highly excited ground state. An automated transition-state search algorithm was employed to identify the corresponding ground-state dissociation channels, and Rice-Ramsperger-Kassel-Marcus and Kinetic Monte Carlo simulations were used to calculate the associated branching ratios. The proposed mechanisms were validated using the experimentally measured and quasi-classical trajectory-deduced nascent internal energy distributions of HCN and HNC. This work, along with previous studies, illustrates the propensity for cyano-containing hydrocarbons to act as photolytic sources for astrophysical HCN and HNC and may help explain the observed overabundance of HNC in astrophysical environments.

Intensities and spectral features of the – potential laser transition of Er3+ centers in CaF2–CeF3 disordered crystal**Project supported by Shanghai Engineering Research Center for Sapphire Crystals, China (Grant No. 14DZ2252500), the Fund of Key Laboratory of Optoelectronic Materials Chemistry and Physics Chinese Academy of Sciences (Grant No. 2008DP17301), the Fundamental Research Funds for the Central Universities of China, the National

A CaF2–CeF3 disordered crystal containing 1.06% of Er3+ ions was grown by the temperature gradient technique. Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve recorded at room temperature, and extended x-ray-absorption fine structure spectra were analyzed with an intention to assess the laser potential related to the transition of Er3+. In addition, the thermal diffusivity of the crystal was measured at room temperature. The analysis of room-temperature spectra revealed that the emission is long-lived with a radiative lifetime value of 5.5 ms, peak emission cross section of , and large spectral width pointing at the tunability of the emission wavelength in the region stretching from approximately 1480 nm to 1630 nm. The energies of the crystal field components for the ground and excited multiplets determined from low-temperature absorption and emission spectra made it possible to predict successfully the spectral position and shape of the room-temperature emission band. Based on the correlation of the optical spectra and dynamics of the luminescence decay, it was concluded that in contrast to Yb3+ ions in heavily doped CaF2 erbium ions in the CaF2–CeF3 crystal reside in numerous sites with dissimilar relaxation rates.

Theoretical analysis of electron vibration interactions and study of photo physical properties in Ce3+ doped Ca2P2O7 nano phosphor capped with SHMP

In the present manuscript, Calcium diphosphate phosphor doped with Cerium and capped with sodium hexametaphosphate has been reported. A theoretical analysis of electron vibration interactions in optical transitions of Ce3+ ions in Ca2P2O7 has been elaborated in brief. The main EVI parameters such as Huang’s Rhys factor and effective phonon energy were determined by evaluating the lowest 5d level of Ce3+ spectrum. The obtained values were used to model the shape of emission band along with estimation of zero phonon line. The fabricated nano phosphor was characterized by powder X-ray diffraction technique. Studies revealed that Ca2P2O7 crystallizes in tetragonal group with square anti prism symmetry. The crystal structure arrangement was found to be non linear in nature with two PO3 groups linked by bridging oxygen forming the diphosphate group. Transmission electron microscopy observations explored nano structural features of the synthesized nano phosphor compound. A study involving SAED and HRTEM on isolated particles was carried out to validate the stabilization of the tetragonal phase. The phosphate functional group of the host was probed by Fourier transform infrared microscopy. Optical properties were examined by evaluating the photoluminescence excitation and emission spectra. Broad emission peaks were observed around 326 nm and 347 nm because of 4f-5d transitions of rare earth activator Ce3+. With the help of TL glow curve measurements, the trap depths were calculated employing peak shape method. Lifetime calculation for the nano phosphor indicates that the aforementioned compound has promising potential for solid state lighting and optoelectronic applications.

Emission of Eu3 + in SiO2-ZnO glass and SiO2-SnO2 glass-ceramic: Correlation between structure and optical properties of Eu3 + ions

SiO2:Eu3+ based free-crack transparent bulk composites containing two types of semiconductor nanoparticles (SnO2 or ZnO) were synthesized by sol-gel process. The results of vibrational spectra (Raman, FT-IR), X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) indicate that the SiO2-SnO2 matrix possess the structure of a glass-ceramic due to the presence of SnO2 nanocrystals with average size of 7±2nm homogeneously distributed in silica matrix whereas the SiO2-ZnO still remain amorphous structure after a heat treatment at 600°C for 1h. The energy transfer from nanoparticles to Eu3+ ions is observed in both composites, but this process is more efficient in the glass-ceramic systems. Moreover, the competition between magnetic dipole and electric dipole transitions of Eu3+ as well as the shape of emission bands depends strongly on the structure of host matrix.

Photoluminescence study of a broad yellow-emitting phosphor K2ZrSi2O7:Bi3+

The photoluminescence of a novel yellow emitting phosphor K2ZrSi2O7:Bi3+ that contains no rare earth ions was investigated. This phosphor was further evaluated as a color converter for white LEDs. The results indicate that K2ZrSi2O7:Bi3+ has strong absorption in 300–400nm region due to the 1S0→3P1 transition of Bi3+. Upon excitation into the 3P1 level of Bi3+, K2ZrSi2O7:Bi3+ gives bright and broad yellow emission (FWHM∼125nm) peaking at 560nm. Except for intensity, the spectral position and shape of the yellow emission band are the same for different concentrations of Bi3+ incorporated K2ZrSi2O7; Both the emission spectra measured at liquid nitrogen temperature (77K) and room temperature have no splitting and they can be well fitted by a single Gaussian profile; time resolved luminescence spectra reveal that the shape of the emission spectra remain unchanged with increasing delay time. These results indicate only one type of Bi3+ center exists in K2ZrSi2O7. Accompanied by a decrease of emission intensity, the emission of Bi3+ is blue-shifted upon heating (λmax=560nm at T=25°C vs. λmax=550nm at T=250°C), which is ascribed to the thermally active phonon-assisted tunneling from the excited states of lower-energy emission band to those of higher- energy emission band. The white light has been reached using K2ZrSi2O7:Bi3+ as a yellow emitting phosphor.

Origin of blue emission of phosphors prepared by a solid-state reaction of Eu3+-doped LaCO3OH with Al2O3 in a hydrogen atmosphere

The phosphor powders prepared by calcining mixtures (1:1, 1:2, and 1:3mol ratios) of Eu3+-doped lanthanum(III) hydroxycarbonate (LaCO3OH:Eu3+) and δ-alumina (δ-Al2O3) powders under a mixed gas flow of H2 and N2 exhibited orange (593 and 617nm) and blue (441nm) emission peaks, which were associated with Eu3+-doped lanthanum aluminate (LaAlO3:Eu3+) and Eu2+-doped lanthanum hexaaluminate (La0.827Al11.9O19.09:Eu2+) phosphors, respectively. The relative amount of the latter phosphor increased with increasing reaction temperature and relative amount of δ-Al2O3 in the mixture. The conclusion that the blue emission is not associated with LaAlO3:Eu2+ but La0.827Al11.9O19.09:Eu2+ was supported by the following experimental results: the reduction of LaAlO3:Eu3+ did not give a blue emission; Eu2+ ions occupied more than one site in the host; the line shape and position of the blue emission band were close to those of the single La0.827Al11.9O19.09:Eu2+ phase. No formation of LaAlO3:Eu2+ might be due to the increase in the ionic radius caused by the reduction of Eu3+ to Eu2+.

Photoluminescence of CaxBa1−xGa2S4:Eu2+ solid solutions in wide excitation intensity and temperature intervals

The detailed investigation of CaxBa1−xGa2S4:Eu2+ solid solutions photoluminescence caused by 5d→4f electronic transitions in Eu2+ ions with x value from 0.1 to 0.9 in wide excitation intensity and temperature intervals was performed. It is shown that the change of x from 0.1 to 0.9 appears in a tune of emission spectrum peak position from 506nm to 555nm with minimal losses in the integral intensity not more than by 8%. The long wavelength shift of the emission spectra was determined as a result of the rise in the crystal field splitting energy of 5d-orbitals of Eu2+ ions in thiogallate host with increasing Ca content, which decreases the energy of the 5d→4f emission transition. The energies of the zero phonon line, red shift and the Stokes shift were defined for x value from 0.1 to 0.9. High temperature stability of the integral emission intensity with a decrease at only 25–40% depending on x value was found in the range from 10K to 400K. It was revealed that the increase in Ca content leads to a reduction of the temperature shift of the emission spectrum whereas at x≥0.5 the shift is absent. The photoluminescence decay time constants were found to be from 305ns to 470ns for x value from 0.1 to 0.9. The extreme stability of the emission band shape and spectral position was found in a wide range of excitation power density from 10−3W/cm2 to 107W/cm2 with a reversable emission efficiency droop only above 2·104W/cm2.

(Invited) Exploiting Luminescence for Measurements of Temperature

Temperature is by far the most-measured physical quantity, and temperature sensors are used by a large extent in daily life, industry, military, medicine, etc., with a market share of about 75%–80% of all sensors. Demands for temperature measurements of moving or contact sensitive objects, difficult to access bodies, objects in hazardous locations, at the nanoscale, in living organisms and cells, have stimulated research on the development of new temperature measurement concepts and temperature probes. Luminescence thermometry is among aspiring concepts capable of meeting aforementioned demands in the future. The changes of luminescence properties of materials with temperature allows some materials to act as sensitive thermometers. The phenomenon become the basis of a new arm in the field of luminescence spectroscopy commonly termed as a luminescence thermometry. This lecture will present a brief introduction into the concept of temperature measurements via luminescence, with the description of the temperature quenching of emission. Then, an overview of different concept modalities of luminescence thermometry will be given including: the steady-state luminescence concepts (use of the emission band shapes and positions, emission intensity and intensity ratios, use of the materials with a single- or multi- emission centers) and concepts based on the temporal changes in emission (emission decay- and rise-times). The most important quantities used to characterize the performance of a measurements (such as temperature sensitivities, temperature and spatial resolution, measurement ranges) will be explained and compared between different measurements modalities as well as between different classes of materials utilized as temperature probes. Finally, several designs of temperature sensing by luminescence in a different application fields will be highlighted.

Study of electron-vibrational interaction in 5d states of Ce3+ ions in the chloroapatite system

Electron-vibrational interaction (EVI) in interconfigurational 5d-4f transition of Ce3+-doped alkaline-earth chlorophosphates, also known as apatites, is studied for the first time in this work. Using the configurational coordinate model, the main EVI parameters such as Huang-Rhys factor, effective phonon energy and the zero-phonon line (ZPL) position are determined for all samples studied. Photoluminescence characteristics of these compounds are utilized to estimate EVI parameters. As a reliable test validating the obtained results, the emission band shape of was modeled to yield good agreement with experimental emission spectra. The values of EVI parameters were systematically compared for all studied materials as well as with similar systems with halide ions.