Intensity Redistribution Research Articles

The effect of magnesium impurities on the optical and spectral characteristics of calcium orthovanadate single crystals doped with chromium and manganese

The effect of magnesium co-doping on growth conditions, crystal composition, optical and spectral properties of manganese or chromium-doped Ca3(VO4)2 (CVO) crystal was studied. The single crystals were grown by the Czochralski method. Effective segregation coefficients of manganese and chromium in the CVO matrix with magnesium co-doping were calculated. A redistribution of the absorption lines intensities was observed in the absorption spectra of CVO:Mn:Mg and CVO:Cr:Mg. Low (15 K) temperature fluorescence measurements confirmed that co-doping CVO crystal with Mg ions leads to the redistribution of Mn ions concentration in different valence states, but does not cause changes in their spectral properties. In the presence of magnesium, additional annealing of the materials resulted in a slower reduction of the valence state of doping ions and a noticeable change in crystal coloration. All investigated impurities have practically no effect on the specific ferroelectric domain structure of CVO.

The Thermal Stability and Photoluminescence of ZnSeO3 Nanocrystals Chemically Synthesized into SiO2/Si Track Templates

We report the effect of high-temperature treatment on the structure and photoluminescence of zinc selenite nanocrystals (ZnSeO3) deposited into SiO2/Si track templates. The templates were formed via irradiation with Xe ions (200 MeV, 108 ions/cm2) followed by etching in HF solution. ZnSeO3 nanocrystals were obtained via chemical deposition from the aqueous solution of ZnCl2 and SeO2 as Zn-, Se- and O-precursors. To estimate the thermal stability of the deposited precipitates, heat treatment was carried out at 800 and 1000 °C for 60 min in a vacuum environment. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), photoluminescence (PL) spectroscopy, and electrical measurements were used for the characterization of ZnSeO3/SiO2nanoporous/Si nanocomposites. Thermal treatment of the synthesized nanocomposites resulted in structural transformations with the formation of ZnSe and ZnO phases while the content of the ZnSeO3 phase decreased. For the as-deposited and annealed precipitates, an emission in the range of (400 to 600) nm was observed. PL spectra were approximated by four Gaussian curves with maxima at ~550 nm (2.2 eV), 488 nm (2.54 eV), ~440 nm (2.82 eV), and 410 nm (3.03 eV). Annealing resulted in a decrease in PL intensity that was possibly due to the weight loss of the deposited substance during high-temperature treatment. The redistribution of maxima intensities after annealing was also observed with an increase in blue and violet emissions. The origin of the observed PL is discussed. The I–V curve analysis revealed an electronic type of conductivity for the ZnSeO3(NCs)/SiO2nanoporous/Si structure. The values of the specific conductivity were calculated within the percolation model. The sample annealed at 800 °C showed the highest specific conductivity of 8.5 × 10−6 Ohm−1·cm−1.

Intervalence Charge Transfer in Aluminum Oxide and Aluminosilicate Minerals at Elevated Temperatures

Abstract Single-crystal optical spectra of corundum (Al2O3) and the Al2SiO5 polymorphs andalusite, kyanite, and sillimanite, containing both Fe2+ – Fe3+ and Fe2+ – Ti4+ intervalence charge transfer (IVCT) absorption bands were measured at temperatures up to 1000 °C. Upon heating, thermally equilibrated IVCT bands significantly decreased in intensity and recovered fully on cooling. These trends contrast with the behavior of crystal field bands at temperature for Fe, Cr and V in corundum, kyanite, and spinel. The effects of cation diffusion and aggregation, as well as the redistribution of band intensity at temperature, are also discussed. The loss of absorption intensity in the visible and near-infrared regions of the spectrum of these phases may point to a more general behavior of IVCT in minerals at temperatures within the Earth with implications for radiative conductivity within the Earth.

CN stretches around 4.4 microns dominate the IR absorption spectra of cyano-polycyclic aromatic hydrocarbons

ABSTRACT Anharmonic quantum chemical computations reveal a strong, narrow (width = 0.075 $\mu$m) band in the 4.3–4.5 $\mu$m region of the absorption spectra of the cyano-substituted polycyclic aromatic hydrocarbons (CN-PAHs) cyanonaphthalene, cyanoanthracene, cyanophenanthrene, and cyanopyrene. This narrow window with intense IR lines implies that CN-PAHs of various shapes and sizes offer little variation in both wavelength and intensity in this region. Subsequently, this band can be used as a tracer for CN-PAHs. The distinct features making up the band are assigned to mixed vibrational states consisting of the CN stretch fundamental and various combination bands, including in-plane CH bends, CC skeletal bends, and CC skeletal breathing motions. The extraordinarily large intrinsic intensity of the fundamental CN stretch is redistributed to nearby states via anharmonic coupling, which is readily captured when using second order vibrational perturbation theory with resonance polyad matrices. This redistribution of intensity leads to a complex spectrum. The intense bands in this wavelength region may contribute to the baseline continuum and undulating macroscopic structure seen in recent JWST NIRSpec observations.

MORPHOLOGICAL, OPTICAL PROPERTIES AND ELECTRONIC STRUCTURE OF ZnO THIN FILMS DOPED WITH ALUMINUM

This paper presents the results of investigation of aluminum-doped zinc oxide thin films obtained by radio-frequency magnetron deposition on a glass substrate. It was shown by energy dispersion X-ray spectroscopy that the average aluminum content in the thin films was 0.2–0.8 at.%. An increase in the average grain size with increasing aluminum concentration was shown, and column-like growth of the films was established using microscopic images. Investigation of the electronic structure showed a redistribution of intensity in the O 1s spectrum with aluminum doping. The valence band spectra were also obtained, and theoretical calculations were performed within the framework of density functional theory to better understanding the results. Using a spectrophotometer, the transparency of the films obtained after aluminum doping was shown to increase. With the help of the Tauc method, the band gap was determined to be 3.41 eV, while DFT calculations showed a band gap of 1.25 eV.

Electrical conductivity, luminescence, and deep acceptor levels in β-Ga2O3-In2O3 polycrystalline solid solution doped with Zr4+ or Ca2+ ions

Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga2O3-In2O3 solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga2O3-In2O3 solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca2+ or Zr4+ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca2+ and was 10−13 Ω−1 cm−1, while in the samples doped with Zr4+, the electrical conductivity was the highest and reached 10−3 Ω−1 cm−1. The broadband luminescence of β-Ga2O3-In2O3 solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca2+ or Zr4+ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Gai, VGa, VGaVo) or doping impurities (Zr4+, Ca2+). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the VGa or VGaVO acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca2+ impurities are manifested in the intense excitation band at 4.1 eV.

Observation of magnetically-induced transition intensity redistribution in the onset of the hyperfine Paschen–Back regime

The Zeeman effect is an important topic in atomic spectroscopy. The induced change in transition frequencies and amplitudes finds applications in the Earth-field-range magnetometry. At intermediate magnetic field amplitude B∼B0=Ahfs/μB, where Ahfs is the magnetic dipole constant of the ground state, and μB is the Bohr magneton (B0≈1.7kG for Cs), the rigorous rule ΔF=0,±1 is affected by the coupling between magnetic sub-levels induced by the field. Transitions satisfying ΔF=±2, referred to as magnetically-induced transitions, can be observed. Here, we show that a significant redistribution of the Cs 6S1/2→6P3/2 magnetically-induced transition intensities occurs with increasing magnetic field. We observe that the strongest transition in the group Fg=3→Fe=5 (σ+ polarization) for B<B0 cease to be the strongest for B>3B0. On the other hand, the strongest transition in the group Fg=2→Fe=4 (σ− polarization) remains so for all our measurements with magnetic fields up to 9kG. These results are in agreement with a theoretical model. The model predicts that similar observations can be made for all alkali metals, including Na, K and Rb atoms. Our findings are important for magnetometers utilizing the Zeeman effect above Earth field, following the rapid development of micro-machined vapor-cell-based sensors.

Spectroscopic Properties of Cobalt Ions in Ca3(VO4)2 Crystals Doped via Thermal Diffusion and During Synthesis

The spectroscopic properties of cobalt ions in Ca3(VO4)2 crystals doped via thermal diffusion and during synthesis are investigated. The diffusion doped crystal shows the potential for higher cobalt doping while maintaining its high initial optical quality. The redistribution of several absorption and fluorescence lines intensities with cobalt concentration is attributed to the formation of Co2+ optical centers with sufficiently different local environments. The fluorescence decay times of Co2+ optical centers are measured to differ by an order of magnitude (95 and 13 μs) and are attributed to centrosymmetric M1 and low symmetry M2 types of Co2+ optical centers, possibly corresponding to Ca(4) and Ca(1) positions of Ca3(VO4)2 crystal, respectively. Nonlinear transmission of Co2+ M2 centers is measured, and efficient absorption cross‐sections of 1.4 × 10−19 and 2.4 × 10−19 cm2 are evaluated at 1300 and 1500 nm, respectively. The narrow fluorescence line of cobalt ions peaking at about 1170 nm, detected in both Ca3(VO4)2 crystals doped via thermal diffusion and during synthesis, is attributed to Co ions in a trivalent state.

Terahertz radiation generation from amplitude-modulated laser filament interaction with a magnetized plasma

The availability of high-power lasers open new frontiers of Terahertz (THz) optics. In this paper, we present a mechanism for the enhanced THz field generation from the laser wakefield excitation during the interaction of an amplitude-modulated laser filament with a magnetized plasma. The derivation of electric and magnetic wakefields in axially magnetized plasma is obtained using the perturbative approach. Amplitude-modulated laser filament generates a significantly stronger transverse current due to laser intensity redistribution by the amplitude modulation. The modulation index of the amplitude modulated laser pulse is used to control the transverse current at THz frequency. Fourfold enhancement takes place in THz field strength for higher values of the modulation index (0–0.4). Also, the conversion efficiency of this mechanism is estimated as [Formula: see text] that can be enhanced for higher modulation index. Scaling laws are provided for controlling and optimization of generated THz field. This work may be crucial in exploring THz optical phenomena such as THz field-induced Kerr effects and many other nonlinear effects.

Peculiarities of Eu3+ Photoluminescence in Opal Photonic Crystal Films and Heterostructures Based of Them

Single opal films and heterostructures based on them grown by the method of vertically moving meniscus are characterized by the reflection spectroscopy technique and then impregnated with the Eu(CH3COO)3 × H2O salt. The suppression of the Eu3+ ion emission in single opal films is clearly detected within the photonic stop-band range. The weaker manifestation of this effect in heterostructures is more likely due to interface defects causing both the appearance of permitted states in the photonic stop band and the scattering of radiation in the direction of observation. With the further impregnation of opal films with glycerol to reduce the dielectric contrast from 1.85 to 1.13, the emission spectrum is mainly determined by the Eu3+ coordination environment effects accompanied with the broadening of bands and the spectral intensity redistribution.

Background optimization of powder electron diffraction for implementation of the e-PDF technique and study of the local structure of iron oxide nanocrystals.

The local structural characterization of iron oxide nanoparticles is explored using a total scattering analysis method known as pair distribution function (PDF) (also known as reduced density function) analysis. The PDF profiles are derived from background-corrected powder electron diffraction patterns (the e-PDF technique). Due to the strong Coulombic interaction between the electron beam and the sample, electron diffraction generally leads to multiple scattering, causing redistribution of intensities towards higher scattering angles and an increased background in the diffraction profile. In addition to this, the electron-specimen interaction gives rise to an undesirable inelastic scattering signal that contributes primarily to the background. The present work demonstrates the efficacy of a pre-treatment of the underlying complex background function, which is a combination of both incoherent multiple and inelastic scatterings that cannot be identical for different electron beam energies. Therefore, two different background subtraction approaches are proposed for the electron diffraction patterns acquired at 80 kV and 300 kV beam energies. From the least-square refinement (small-box modelling), both approaches are found to be very promising, leading to a successful implementation of the e-PDF technique to study the local structure of the considered nanomaterial.

Enhanced Photoluminescence and Random Lasing Emission in TiO2-Decorated FAPbBr3 Thin Films.

Herein, titanium-dioxide-decorated organic formamidinium lead bromide perovskite thin films grown by the one-step spin-coating method are studied. TiO2 nanoparticles are widespread in FAPbBr3 thin films, which changes the optical properties of the perovskite thin films effectively. Obvious reductions in the absorption and enhancements in the intensity of the photoluminescence spectra are observed. Over 6 nm, a blueshift of the photoluminescence emission peaks is observed due to 5.0 mg/mL TiO2 nanoparticle decoration in the thin films, which originates from the variation in the grain sizes of the perovskite thin films. Light intensity redistributions in perovskite thin films are measured by using a home-built confocal microscope, and the multiple scattering and weak localization of light are analyzed based on the scattering center of TiO2 nanoparticle clusters. Furthermore, random lasing emission with sharp emission peaks is achieved in the scattering perovskite thin films with a full width at the half maximum of 2.1 nm. The multiple scattering of light, the random reflection and reabsorption of light, and the coherent interaction of light within the TiO2 nanoparticle clusters play important roles in random lasing. This work could be used to improve the efficiency of photoluminescence and random lasing emissions, and it is promising in high-performance optoelectrical devices.

Trap state and exciton luminescence of colloidal PbS quantum dots coated with thioglycolic acid molecules

This work presents the results of studying the IR luminescence of colloid PbS quantum dots coated with molecules of thioglycolic acid. Luminescence of the sample was recorded using the InGaAs image sensor PDF 10C/M (ThorlabsInc., USA) and a diffraction monochromator with 600 mm-1 grating. To study the temperature dependence of luminescence, the sample was cooled in a nitrogen cryostat down to 80 К. A redistribution of the luminescence intensity between two peaks (1100 and 1280 nm) was identified upon a decrease in temperature. It was shown that an exciton absorption peak was present in the excitationspectrum for the short-wave luminescence peak, and the Stokes shift was ΔEstokes ~ 0.1 eV. On the contrary, the exciton peak was absent in the luminescence excitation spectrum of the long-wave band, and its red boundary was shifted towards the short-wave region, that provided the Stokes shift of more than 0.3 eV. It was concluded that the short-wave luminescence band appeared as a result of the radiative annihilation of an exciton, while the long-wave band appeared due to the recombination of charge carriers at trap states. Trap state luminescence was effectively excited upon direct absorption of the radiation by the luminescence centre. A three-level diagram was suggested that determined the IR luminescence of colloid PbS quantum dots coated with thioglycolic acid molecules.

Effect of laser intensity redistribution on terahertz field generation via laser wakefield in a magnetized plasma

Effect of laser intensity redistribution on terahertz field generation via laser wakefield in a magnetized plasma

Nanopore-enabled macroscopic alignment of 700 kDa membrane protein complex: Characterization by pulsed EPR

The Photosystem II (PSII) catalytic cycle involves proton transfer as well as rearrangements of hydrogen bonding of sidechains and cofactors and their reorientation. While thought to be critically important for the function, some of the changes including protonation states of the cofactors and metal cluster ligands are inaccessible by x-ray crystallography but can be addressed in EPR experiments with macroscopically aligned PSII embedded in lipid membranes. Previously, we reported on aligning lipid bilayers within anodic aluminum oxide nanopores (AAO) 40 to 90 nm in diameter. The method provides for lipid alignment within 2-3o mosaic spread and worked well for single domain membrane proteins. Here, we successfully address a challenge of aligning a much larger membrane protein complex - ca. 700-kDa dimer of PSII. This was accomplished by developing AAO substrates with 300-400-nm pore diameter and 80 μm in length and forming nanotubular PSII bilayer inside the pores by self-assembly directly from aqueous suspensions. After the deposition, the nanoporous substrates acquired dark green color indicative of PSII complexes in high density. AAO strips were exposed to ambient light for 10 min at room temperature to generate YD⦁ radical species. The shock frozen samples retained macroscopic alignment of PSII as revealed by EPR. The angle dependent hyperfine interactions with 3- and 5-ring protons were measured in 2D HYSCORE experiments at two orthogonal sample orientations in magnetic field, B0. The two spectra exhibited well-pronounced differences caused by intensity redistributions among the cross-peaks arising from different orientations of hyperfine tensors vs. B0 and provided angular restrains for the tensor orientation with respect to the bilayer normal. Spectral resolution was also improved by decreasing HYSCORE peak crowding from the macroscopic alignment.

Особенности флуоресценции паров атомов Rb, заключенных в ячейку с антирелаксационным покрытием

The features of the fluorescence spectra of Rb D1 line vapors were studied for the first time using a cell with anti-relaxation PolyDiMethylSiloxane (PDMS) coating. At high intensities (&gt; 200mW/cm2) of a cw narrow-band diode laser in the transmission spectra due to the effect of optical pumping, there are no absorption lines at atomic transitions, while in the fluorescence spectrum, all 8 atomic transitions of the D1 line are pronounced. A strong redistribution of fluorescence intensity is registered for atomic transitions of 85Rb and 87Rb: in particular, the ratio of fluorescence amplitudes for transitions of 87Rb, Fg = 1 - Fe = 1, 2 in a regular cell is 5, while for a PDMS cell it is equal to 1.5. A physical explanation of the observed features of fluorescence in a PDMS cell is given. A significant increase of fluorescence intensity and a change in redistribution at the transitions with increasing of the PDMS cell temperature is demonstrated. It is noted that at large intensities of laser radiation (when there are no peaks on the transmission/absorption spectra of atomic transitions), fluorescence spectra remain the only convenient and informative tool for studying the behavior of atoms.

Subtle hydrogen bond preference and dual Franck-Condon activity - the interesting pairing of 2-naphthol with anisole.

The hydrogen-bonded complexes between 2-naphthol (or β-naphthol) and anisole are explored by detecting their IR absorption in the OH stretching range as well as their UV absorption by means of laser-induced fluorescence and resonance-enhanced two-photon UV ionisation. For the more stable cis and the metastable trans conformations of the OH group in 2-naphthol, hydrogen bonding to the oxygen atom of anisole is consistently detected in different supersonic jet expansions. Alternative hydrogen bonding to the aromatic ring of anisole remains elusive, although the majority of state-of-the-art hybrid DFT functionals with London dispersion correction and - less surprisingly - MP2 wavefunction theory predict it to be slightly more stable at zero-point level, unless three-body dispersion correction is added to the B3LYP-D3(BJ) approach. This changes at the CCSD(T) level, which forecasts an energy advantage of 1-3 kJ mol-1 for the classical hydrogen bond arrangement even after including (DFT) zero-point energy contributions. The UV and IR spectra of the cis complex exhibit clear evidence for intensity redistribution of the primary OH stretch oscillator to combination states with the same low-frequency intermolecular bending mode by Franck-Condon-type vertical excitation mechanisms. This rare case of dual (vibronic and vibrational) Franck-Condon activity of a low-frequency mode invites future studies of homologues where aromatic ring docking of the OH group may be further stabilised, e.g. through anisole ring methylation.

Contribution of multiple plasmon scattering in low-angle electron diffraction investigated by energy-filtered atomically resolved 4D-STEM

We report the influence of multiple plasmon losses on the dynamical diffraction of high-energy electrons, in a scanning transmission electron microscopy (STEM) study. Using an experimental setup enabling energy-filtered momentum-resolved STEM, it is shown that the successive excitation of up to five plasmons within the imaged material results in a subsequent and significant redistribution of low-angle intensity in diffraction space. An empirical approach, based on the convolution with a Lorentzian kernel, is shown to reliably model this redistribution in dependence of the energy-loss. Our study demonstrates that both the significant impact of inelastic scattering in low-angle diffraction at elevated specimen thickness and a rather straightforward model can be applied to mimic multiple plasmon scattering, which otherwise is currently not within reach for multislice simulations due to computational complexity.

Laser pulse shaping in a semiconductor material

We present a model representing the intensity redistribution of a laser when propagating inside an n-InSb semiconductor material. The intensity-dependent behavior of the refractive index of the semiconductor is responsible for the laser focusing, which leads to laser intensity redistribution. The beam width parameter (f) equation is obtained assuming paraxial approximations. Numerical simulations are performed to measure the variation in the intensity of the laser. A significant change in laser intensity is observed. We predict that our model may be helpful in plasma acceleration.

Dynamics of degenerate and nondegenerate solitons in the two-component nonlinear Schrödinger equations coupled to Boussinesq equation

The paper studies the dynamics of degenerate and nondegenerate bright solitons and their collisions in the two-component nonlinear Schrödinger equations coupled to Boussinesq equation. The degenerate solitons that have only single-hump profiles, exhibit both elastic and inelastic collisions, and their velocities are identical in the two short wave (SW) components and in the long wave (LW) component. The nondegenerate single solitons have two different forms: one of them has double- or single-hump profiles and identical velocities in all SW and LW components, and the other one only admits single-hump profiles and has unequal velocities in the two SW components. The collisions of nondegenerate solitons cannot result in the redistribution of soliton intensities. Three different types of collisions of nondegenerate two-soliton solutions are studied in detail.