Resolved Emission Spectra Research Articles

Stokes shift microscopy by excitation and emission imaging.

In this contribution, we present a new method, based on a tunable excitation laser source and a robust common path interferometer in the detection channel. Its purpose is to image spectral excitation and emission information on a monochrome complementary metal oxide semiconductor (CMOS) camera. This allows us to spatially obtain both excitation and emission spectra of the whole imaged area and create derived images such as red-green-blue (RGB), excitation and emission maxima, and Stokes shift images. Our presented method is a further development of hyperspectral imaging that usually is limited to recording spatially resolved emission spectra. Taking advantage of the full camera chip should speed up the acquisition versus line scan or pointwise hyperspectral imaging.

Vibrationally resolved emission spectra of luminescent conjugated oligothiophenes from anharmonic calculations.

We report on accurate and efficient calculations of vibrationally resolved emission spectra for oligothiophenes from anharmonic vibrational configuration interaction wave-function calculations in reduced vibrational spaces. These reduced spaces are chosen based on the independent mode displaced harmonic oscillator model. Good agreement with experiment is obtained for all-trans oligothiophenes with two to five rings also when employing only a few active modes. Vibrational modes incorporating inter-ring carbon-carbon stretches and a ring breathing mode are found to be the main players in the vibrational progression for the emission from the first excited electronic state for all investigated oligothiophene derivatives. The presented framework is here illustrated for oligothiophenes, but we have made no underlying system-dependent assumptions and believe it to become a valuable tool for the rational design of fluorescence biomarkers.

What accounts for the color purity of tetradentate Pt complexes? A computational analysis.

In order to improve the texture of human visual perception and broaden the range of certain optical applications, many phosphorescent complexes exhibiting narrow emission spectra have been prepared through reasonable molecular design. For example, by adding a particular group such as tert-butyl (tbu) to a suitable position of PtON1 and PtON7, the peak width of a relevant vibronic band caused by the specific vibrational normal modes could be dramatically restrained in the emission spectra at room temperature. For the purpose of finding an effective approach to replace the trial-and-error manner, the microscopic mechanism of such high color purity was elucidated by computational investigation. In this study, we aim to identify the reason that causes sharp emission associated with the relevant vibrational normal modes. Here, these modes can be labeled to the emission peak by the vibrationally resolved emission spectra. Based on the displacement vectors of relevant normal modes and the vibrationally resolved spectra, the most possible reason for the higher color purity is that tbu in a specific location can restrain the structural deformation between the first triplet excited state (T1) and the ground state (S0). That is to say, the relevant Huang-Rhys factor (Sk) of specific vibrational modes would be decreased. For these compounds, the total bandwidth and the height of the intermediate and high-frequency regions which are in direct proportion to Sk would be decreased to obtain the higher color purity by tbu in a particular position. What is more, the best position for tbu in order to suppress the structural deformation was also considered. In the meantime, radiative (kr) and nonradiative (knr) decay rates of T1 were investigated to seek the effective phosphorescent complexes.

Near-infrared Zeeman spectroscopy for the spatially resolved measurement of helium emission spectra in Heliotron J

A passive spectroscopic method that can measure spatially resolved emission spectra only by observing from a single diagnostic port without assuming plasma symmetry was applied to the stellarator-heliotron device Heliotron J. The emission spectra from the inboard and outboard sides were separated using the difference in their Zeeman effects. On the basis of the fact that in a spectrum as a function of the wavelength, the magnitude of the wavelength splitting by the Zeeman effect relative to the Doppler broadening increases with the wavelength, the method was applied to a near-infrared helium emission line (He I 1s2s 3S−1s2p 3P, 1083 nm), and it was confirmed that the uncertainty in the separated spectra was reduced compared with that in the application to visible emission lines. From the emissivity of the separated spectra, the local recycling flux was evaluated using the inverse photon efficiency method.

Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition.

A microwave (MW) activated hydrogen plasma operating under conditions relevant to contemporary diamond chemical vapor deposition reactors has been investigated using a combination of experiment and self-consistent 2-D modeling. The experimental study returns spatially and wavelength resolved optical emission spectra of the d → a (Fulcher), G → B, and e → a emissions of molecular hydrogen and of the Balmer-α emission of atomic hydrogen as functions of pressure, applied MW power, and substrate diameter. The modeling contains specific blocks devoted to calculating (i) the MW electromagnetic fields (using Maxwell's equations) self-consistently with (ii) the plasma chemistry and electron kinetics, (iii) heat and species transfer, and (iv) gas-surface interactions. Comparing the experimental and model outputs allows characterization of the dominant plasma (and plasma emission) generation mechanisms, identifies important coupling reactions between hydrogen atoms and molecules (e.g., the quenching of H( n > 2) atoms and electronically excited H2 molecules (H2*) by the alternate ground-state species and H3+ ion formation by the associative ionization reaction of H( n = 2) atoms with H2), and illustrates how spatially resolved H2* (and Hα) emission measurements offer a detailed and sensitive probe of the hyperthermal component of the electron energy distribution function.

Electronic bands of scandium monocarbide, ScC, in the region 14 140-16 000 cm-1.

Scandium monocarbide molecules, ScC, have been prepared by the reaction of 532 nm laser-ablated Sc metal with acetylene or methane under supersonic jet-cooled conditions. Electronic spectra of Sc12C and Sc13C have been recorded in the region 14 140-16 000 cm-1 using laser-induced fluorescence, and about 40 bands of each isotopomer have been analyzed rotationally. Wavelength resolved emission spectra have been obtained for many of them. The results show that Sc12C has a 2Πi ground state, with a bond length of 1.952 Å. Its vibrational frequency and spin-orbit coupling constant are 648 cm-1 and -39.47 cm-1, respectively (631 cm-1 and -39.32 cm-1 in Sc13C). Lying 155.58 cm-1 above the X2Π3/2 level (154.72 cm-1 in Sc13C) is a 4Π5/2 level, the lowest spin-orbit component of a 4Πi state. The excited states at higher energy are very complicated. Bands from both the doublet and quartet spin manifolds are present, and there are strong doublet-quartet interactions which induce many nominally-forbidden bands violating the selection rule ΔS = 0. Eight excited electronic states have been recognized, including four 4Δ states. These 4Δ states represent four of the five 4Δ states from the electron configurations (C 2pσ)2 (C 2pπ)2 (Sc 3dδ)1 and (C 2pσ)1 (C 2pπ)2 (Sc 4sσ)1 (Sc 3dδ)1.

Self-organized patterns by a DC pin liquid anode discharge in ambient air: Effect of liquid types on formation

A pin liquid anode DC discharge is generated in open air without any additional gas feeding to form self-organized patterns (SOPs) on various liquid interfaces. Axially resolved emission spectra of the whole discharge reveal that the self-organized patterns are formed below a dark region and are visible mainly due to the N2(C 3Π − B 3Π) transitions. The high energy N2(C) level is mainly excited by the impact of electrons heated by the local increased electric field at the interface. For the first time, the effect of the liquid type on the SOP formation is presented. With almost the same other discharge conditions, the formed SOPs are significantly different from HCl and H2SO4 liquid anodes. The SOP difference is repeated when the discharge current and gap distance change for both liquid anodes. The variations of SOP size and discretization as a function of discharge current and gap distance are discussed and confirm that different SOPs are formed by the HCl liquid anode from tap water or the H2SO4 liquid anode. A possible explanation is brought up to explain the dependence of SOPs on the liquid type.

Half-disk laser: insight into the internal mode structure of laser resonators.

Usually electromagnetic modes inside a laser resonator are a matter of the theoretical studies. In a sense we manage "to have a look into a whispering gallery mode (WGM) resonator" and observe how the resonator modes arrange in reality. The picture occurs to be quite different from the commonly used Bessel modes in a disk resonator. A chance to explore optical modes inside a resonator appears in a WGM laser with a cleaved cavity. The flat laser facet gives an opportunity to study both far and near field patterns formed by different modes. In this research we use a high resolution technique of detection of laser emission based on an atomic force microscope, which allowed us to visualize even high Q modes normally sealed inside the resonator. This information was completed with spatially resolved emission spectra and far-field patterns measured using an infrared camera. The analysis of the obtained results using both wave and geometrical optics approaches and finite elements simulations showed that emission of the studied devices is governed by a few low order optical modes experiencing a small number of reflections from the resonator walls. These modes can be considered as counter propagating Gaussian beams and their interference at the laser facet was also observed in the experiment. This work showed that, contrary to conventional ridge or surface emitting lasers, in such deformed disk resonators outputs of different optical modes are spatially separated and can be studied individually along the cleaved facet of the laser.

Vibronic Coupling Analysis of the Ligand-Centered Phosphorescence of Gas-Phase Gd(III) and Lu(III) 9-Oxophenalen-1-one Complexes

The gas-phase laser-induced photoluminescence of cationic mononuclear gadolinium and lutetium complexes involving two 9-oxophenalen-1-one ligands is reported. Performing measurements at a temperature of 83 K enables us to resolve vibronic transitions. Via comparison to Franck-Condon computations, the main vibrational contributions to the ligand-centered phosphorescence are determined to involve rocking, wagging, and stretching of the 9-oxophenalen-1-one-lanthanoid coordination in the low-energy range, intraligand bending, and stretching in the medium- to high-energy range, rocking of the carbonyl and methine groups, and C-H stretching beyond. Whereas Franck-Condon calculations based on density-functional harmonic frequency computations reproduce the main features of the vibrationally resolved emission spectra, the absolute transition energies as determined by density functional theory are off by several thousand wavenumbers. This discrepancy is found to remain at higher computational levels. The relative energy of the Gd(III) and Lu(III) emission bands is only reproduced at the coupled-cluster singles and doubles level and beyond.

The Role of a Phonon Bottleneck in Relaxation Processes for Ln-Doped NaYF4 Nanocrystals

The localized inner 4f shell transitions of lanthanide ions are largely independent of the local surroundings. The luminescence properties of Ln3+ ions doped into nanocrystals (NCs) are therefore similar to those in bulk crystals. Quantum size effects, responsible for the unique size-dependent luminescence of semiconductor NCs, are generally assumed not to influence the optical properties of Ln3+-doped insulator NCs. However, phonon confinement effects have been reported to hamper relaxation between closely spaced Stark levels in Ln3+-doped NCs. At cryogenic temperatures emission and excitation from higher Stark levels was observed for Ln3+ ions in NCs only and were explained by a cutoff in the acoustic phonon spectrum. Relaxation would be inhibited as no resonant low energy (long wavelength) acoustic phonon modes can exist in nanometer sized crystals, and this prevents relaxation by direct phonon emission between closely spaced Stark levels. This phenomenon is known as a phonon bottleneck. Here, we investigate the role of phonon confinement in Ln-doped NCs. High resolution emission spectra at temperatures down to 2.2 K are reported for various Ln3+ ions (Er3+, Yb3+, Eu3+) doped into monodisperse 10 nm NaYF4 NCs and compared with spectra for bulk (microcrystalline) material. Contrary to previous reports, we find no evidence for phonon bottleneck effects in the emission spectra. Emission from closely spaced higher Stark levels is observed only at high excitation powers and is explained by laser heating. The present results indicate that previously reported effects in NCs may not be caused by phonon confinement.

Probing of Reorganization Dynamics within the Different Phases of Themotropic Liquid Crystals

AbstractSolvent properties of two liquid crystalline solvents (LCs), 4‐n‐pentyl‐4/‐cyanobiphenyl (5CB) and 4‐n‐octyl‐4/‐cyanobiphenyl (8CB) are studied by exploiting their intrinsic fluorescence. Solvation dynamics of LCs in crystalline, liquid crystalline and liquid phases are observed by utilizing the dynamic Stokes shift in the time resolved emission spectrum (TRES) of an excited dye molecule coumarin 153 (C153) immersed within the LCs. With increasing temperature, transitions occur from crystalline to smectic/nematic and finally to liquid phase for these thermotropic LCs. At high temperature, liquid crystalline phases with substantial orientational orders are transformed to isotopic liquid phases. In this phase, peak positions of intrinsically fluorescent LCs are shifted towards the higher energy side with lowering its fluorescence quantum yields (φf) as compared to the emission peak positions and quantum yields of LCs in other anisotropic phases. Solvation dynamics study shows that the average solvation time of C153, immersed within the liquid phases of LCs, is about an order of magnitude faster as compared to that within a crystalline phase of the same substrate (5CB or 8CB). This observation is substantiating the fact that even within a complete crystalline phase a fluid like motion of the LC solvent molecules still exists. Average solvation time of C153 follows a descending order when we move from a complete crystalline phase to liquid crystalline phase to complete liquid phase.

Solvatochromic Property in Lipid Bilayer Interphases Evaluated from the Deconvolution of Time Resolved Emission Spectrum of Laurdan

Solvatochromic Property in Lipid Bilayer Interphases Evaluated from the Deconvolution of Time Resolved Emission Spectrum of Laurdan

The phycobilisome terminal emitter transfers its energy with a rate of (20 ps)\u20131 to photosystem II

Ultrafast time resolved emission spectra were measured in whole cells of a PSI-deficient mutant of Synechocystis sp. PCC 6803 at room temperature and at 77K to study excitation energy transfer and trapping. By means of a target analysis it was estimated that the terminal emitter of the phycobilisome, termed allophycocyanin 680, transfers its energy with a rate of (20 ps)–1 to PSII. This is faster than the intraphycobilisome energy transfer rates between a rod and a core cylinder, or between the core cylinders.

A surface-hopping method for semiclassical calculations of cross sections for radiative association with electronic transitions.

A semiclassical method based on surface-hopping techniques is developed to model the dynamics of radiative association with electronic transitions. It can be proven that this method is an extension of the established semiclassical formula used in the characterization of diatomic molecule-formation. Our method is tested for diatomic molecules. It gives the same cross sections as the former semiclassical formula but, contrary to the former method, it allows us to follow the fate of the trajectories after the emission of a photon. This means that we can characterize the rovibrational states of the stabilized molecules. Using semiclassical quantization, we can obtain quantum state-resolved cross sections or emission spectra for the radiative association process. The calculated semiclassical state-resolved spectra show general agreement with the result of quantum mechanical perturbation theory. Furthermore, our surface-hopping model is not only applicable for the description of radiative association but it can be used for semiclassical characterization of any molecular process where spontaneous emission occurs.

Fourier transform emission spectra and deperturbation analysis of the A2Π – X2Σ+ and B2Σ+ – X2Σ+ electronic transitions of ZnH

A discharge-furnace emission source was used to generate the A2Π→X2Σ+ and B2Σ+→X2Σ+ spectra of ZnH radical. High resolution emission spectra were recorded with a Fourier transform spectrometer, and several bands have been assigned for the 64ZnH major isotopologue. The data span the v″=0–6 levels of the X2Σ+ ground state, the v′=0–3 levels of the A2Π state, and the v′=0–2 levels of the B2Σ+ state, extending to high rotational quantum numbers near and above the dissociation asymptote of the ground state. Large local perturbations were observed in the A2Π and B2Σ+ electronic states, and a deperturbation analysis was carried out using a single Hamiltonian matrix that includes 2Π and 2Σ+ matrix elements, as well as off-diagonal elements coupling vibrational levels of the two electronic states. Band constants and Dunham coefficients were obtained for the A2Π and B2Σ+ excited states by least-squares-fitting of all the experimental data. The equilibrium vibrational constants ωe and ωexe have been determined to be 1907.528(4) and 38.674(2)cm−1, respectively, for the A2Π state, and 1021.135(94) and 17.725(80)cm−1, for the B2Σ+ state, and the equilibrium Zn–H distances (re) are 1.511662(2)Å and 2.26805(7)Å for the A2Π and B2Σ+ states, respectively. The RKR potential curves were constructed for the A2Π and B2Σ+ states, and vibrational radial overlap integrals were computed. The off-diagonal matrix elements coupling the electronic wavefunctions of the A2Π and B2Σ+ states, i.e., a+ and b, were determined to be 228±3cm−1 and 0.73±0.01, respectively, for the ZnH molecule.

Fourier transform emission spectra of the A2Π → X2Σ+ and B2Σ+ → X2Σ+ transitions of ZnD

High resolution emission spectra of ZnD have been recorded in the 18000–27000cm−1 region using a Fourier transform spectrometer, and two electronic transitions have been observed. The A2Π→X2Σ+ data span the v″=0 to 6 levels of the X2Σ+ ground state, and the v′=0 to 3 levels of the A2Π state. In the B2Σ+→X2Σ+ transition, the v′=0 progression was observed for the first time, including the 0–4, 0–5, 0–6 and 0–7 bands. Local perturbations were observed between the v′=0 levels of the B2Σ+ state and the v′=2 and 3 levels of the A2Π state. Spectroscopic constants were determined for the X2Σ+, A2Π and B2Σ+ states of 64ZnD from rotational analysis of the data. The equilibrium ZnD bond distances (re) have been determined to be of 1.51176(1) and 2.26714(1)Å, for the A2Π and B2Σ+ states, respectively.

Band bending effect induced non-enzymatic highly sensitive glucose sensing in ZnO nanoparticles

We report band bending effect assist the enhancement of green fluorescence in ZnO nanoparticles surrounded by glucose molecules. Optical absorption measurements show free exciton absorption of ZnO around 377nm and consistent decrease in absorption intensity while adding glucose. Room temperature photoluminescence study under excitation at 330nm shows very strong emission in the ultra violet (UV) and visible wavelength regions. Enhancement in green emission intensity is observed while increasing concentration of glucose from 60 to 480nM, which is attributed for decreasing depletion layer width near the surface as a result of electrons donating by glucose. Recorded time resolved emission spectra of prepared nanoparticles in the presence and absence of glucose proves that there is no energy transfer process occurs during ZnO-glucose interaction and the enhanced green emission are due to glucose molecules adsorbed on the surface of ZnO which can be applied for non-enzymatic glucose sensing applications.

Steady state and time resolved optical characterization studies of Zn2SnO4 nanowires for solar cell applications

Nanowires are a promising option for sensitized solar cells, sensors, and display technology. Most of the work thus far has focused on binary oxides for these nanowires, but ternary oxides have advantages in additional control of optical and electronic properties. Here, we report on the diffuse reflectance, Low Temperature and Room Temperature Photoluminescence (PL), PL excitation spectrum, and Time Resolved PL (TRPL) of Zinc Tin Oxide (ZTO) nanowires grown by Chemical Vapor Deposition. The PL from the ZTO nanowires does not exhibit any band gap or near gap emission, and the diffuse reflectance measurement confirms that these ZTO nanowires have a direct forbidden transition. The broad PL spectrum reveals two Gaussian peaks centered at 1.86 eV (red) and 2.81 eV (blue), representing two distinct defect states or complexes. The PL spectra were further studied by the Time Resolved Emission Spectrum and intensity dependent PL and TRPL. The time resolved measurements show complex non-exponential decays at all w...

Ultrashort pulsed laser induced heating-nanoscale measurement of the internal temperature of dielectrics using black-body radiation

The nanoscale measurement of temperature in the bulk of dielectrics initiated by a single ultrashort laser pulse was first investigated by black-body radiation. A structureless broad continuum emission has been recorded at an interval delay of 2ns with a temporal gate of 2ns and spectral resolution of about 0.137nm, which provides the highest temporal and spectral precision ever. The temporally resolved emission spectrum was proved to be black-body radiation in nature, and temperature was obtained by fitting the radiation with the Planckian formula. Pulse energy was varied from 110 to 270μJ at 600fs and a pulse duration of 0.83ns was also used. The temperature exhibited a small variation with an increasing pulse energy at 600fs. However, due to the energy transfer from heated electrons to lattice, the temperature was sharply increased at pulse duration of 0.83ns. It was estimated that heat accumulation started at 0.42-0.47MHz for a laser pulse at 600fs, while it was 0.25MHz for a laser pulse at 0.83ns.

A New Approach of Oil Spill Detection Using Time-Resolved LIF Combined with Parallel Factors Analysis for Laser Remote Sensing.

In hope of developing a method for oil spill detection in laser remote sensing, a series of refined and crude oil samples were investigated using time-resolved fluorescence in conjunction with parallel factors analysis (PARAFAC). The time resolved emission spectra of those investigated samples were taken by a laser remote sensing system on a laboratory basis with a detection distance of 5 m. Based on the intensity-normalized spectra, both refined and crude oil samples were well classified without overlapping, by the approach of PARAFAC with four parallel factors. Principle component analysis (PCA) has also been operated as a comparison. It turned out that PCA operated well in classification of broad oil type categories, but with severe overlapping among the crude oil samples from different oil wells. Apart from the high correct identification rate, PARAFAC has also real-time capabilities, which is an obvious advantage especially in field applications. The obtained results suggested that the approach of time-resolved fluorescence combined with PARAFAC would be potentially applicable in oil spill field detection and identification.