Absorption Edge Spectra Research Articles

Features of the management of the rule of Urbakh in ZnSe:Yb crystals

A comparative analysis of the edge absorption spectra measured in the temperature range of 290–470 K for two types of zinc selenide substrates has been carried out. It has been established that the self-absorption edge of pure ZnSe: Yb melt crystals is described by the «crystalline» approximation of the general Urbach rule, which is a consequence of dynamic disordering. In samples doped with ytterbium, at 330 K, a reversible transition from dynamic to static disordering was detected, which is described by the “glassy” approximation of the general Urbach rule.

Characterisation of Mn/Ti layered double hydroxide for methylene blue degradation with Bayesian representation of electron transport

The exceptional electron transport mechanism involving layered double hydroxides (LDHs) have led visible light mediated photocatalysis to gain significant interest towards wastewater treatment. LDHs inherently have remarkable photocatalytic characteristics owing to their capability to vary the metal ions and its ratios in the interstitial regions, layered architecture resembling brucite, variable interlayer distance etc. The work presents the hydrothermal synthesis and characterisation of 4:1 Mn/Ti LDH, analyses the impact of Ti4+ doping with Mn2+ on the absorption edge spectra, offers insights into the basic crystal structure via data mining through cross-validation of actual XRD data, and delivers assessments of shifts in its energy density through Bayesian distribution using Markov chain Monte Carlo simulations. The characterisations indicated crystallinity; multiple narrow band-gaps; deformed hexagonally layered sheets and the presence of CO32- and H2O in the interlayer galleries of the LDH. Bayesian analyses provided 95 % credible interval estimates (CrI) for the conduction and valence band energies at varying temperature for evaluating the uncertainty of electron transport across the band-gap. Leveraging on Methylene blue (MB) photocatalysis as a test reaction, the electron transport across the LDH was investigated and it was observed that the material exhibited 92.30 % degradation at 90 min under visible light. The present study further discloses the effects of LDH concentration, time variation, solution pH, and MB concentration on the overall photocatalytic MB degradation. On the basis of the theoretical observations and experimental results, a plausible mechanistic pathway of electron transport has been presented, based on e−−h+hopping conduction model. The positive outcome of this research demonstrates the potential of Mn/Ti LDH as an effective and reusable photocatalyst for wastewater treatment processes.

Evolutions of the optical properties in green-emitting MAPbBr3 perovskite nanoplatelets/polymethyl methacrylate (PMMA) composite films for light-emitting diode applications

Organometal halide perovskites have been gaining tremendous attention for their potential application as optoelectronic devices, owing to their excellent optical and electronic properties. This work fabricated MAPbBr3/PMMA composite film with bright green emission via a simple drop-casting method. It is found that when MAPbBr3 were combined with PMMA, PL peak position and edge absorption spectra exhibit a redshift phenomenon. Comprehensive characterizations using x-ray diffraction (XRD) and transmission electron microscope (TEM) suggested that this phenomenon possibly corresponded to the dielectric screening and strain of perovskite crystal induced by the presence of PMMA. Understanding this redshift phenomenon could be beneficial for developing high color purity optoelectronic devices. A potential application of the prepared film as a green down-converter is also demonstrated. Applying the MAPbBr3/PMMA film on a UV LED has successfully generated green color at (0.21, 0.71), close to the green color standards, i.e., NTSC 1953 and Adobe RGB 98. This result suggests that MAPbBr3 perovskite nanoplatelets/PMMA composite films have great potential for light-emitting device applications.

Determination of the crystal field and nature of x-ray linear dichroism for Co-O with local octahedral, tetrahedral, and tetragonal symmetries

Cobalt oxides with multiple local Co-O coordination environments such as octahedral, tetrahedral, and tetragonal networks display versatile electronic and magnetic properties which have attracted great interest in many fields. Understanding the ground-state properties and determining the fundamental band gap remain challenges in cobalt-based compounds and thin films, which have been investigated here using synchrotron-based Co ${L}_{23}$-edge x-ray absorption measurements followed by configuration interaction cluster calculations. We focus on the detailed Co ${L}_{23}$-edge absorption spectral variations in different octahedral crystal fields as well as in the less investigated tetrahedral and tetragonal systems, taking into account Co ions with different valence states. From a quantitative comparison between the simulated spectrum and an accurately measured absorption spectrum of a specified compound, the crystal field value can be extracted from the Co ${L}_{23}$-edge absorption spectrum, which is complementary to the results obtained in optical measurements and other calculations. Furthermore, Co ${L}_{23}$-edge x-ray linear dichroism shows the same spectral evolutions as a result of either local ${\mathrm{CoO}}_{6}$ cluster with tetragonal symmetry or the magnetic exchange field, whereas both coexist in most antiferromagnetic cobalt oxide thin films. Detailed temperature and polarization-dependent Co ${L}_{23}$-edge absorption measurements have been proposed to distinguish both contributions, which show different spectral variations due to the specified modifications of the ground and final states at different temperatures. Our results offer theoretical guidance for understanding the multiplet structure of Co ${L}_{23}$-edge absorption spectrum, obtaining the precise crystal field value for cobalt oxides with versatile coordinations, and explaining the underlying mechanism of x-ray linear dichroism, as well as understanding the fundamental physical properties and their potential applicability of cobalt oxides and their thin films.

Paramagnetic Conducting Metal–Organic Frameworks with Three‐Dimensional Structure

3D well-crystallized metal-organic frameworks (MOFs), M-THBQ (M=Fe, Co, Mn, THBQ=tetrahydroxybenzoquinone), are synthesized and characterized. Their structures are determined as cubic cell in the group of Pm from powder X-ray diffraction data, and their properties of electronic, magnetic and spectroscopic are also investigated. They are all semiconductors, and Fe-THBQ exhibits the air-stable n-type thermoelectric characteristic as its Seebeck coefficient reaches -130 μV K-1 , and the electrical conductivity is 2.7×10-4 S cm-1 at 300 K. Additional, M-THBQ are paramagnetic, and the value of Weiss constant of Fe-THBQ is -219.37 K, indicating the existence of robust intramolecular antiferromagnetic exchanges. Meanwhile, they display strong absorption bands in the range of 220 to 1000 nm, suggest M-THBQ could have the potential to become photoabsorbers, and Fe-THBQ exhibits a narrow band gap of 0.63 eV according to the ultraviolet absorption edge spectrum.

Paramagnetic Conducting Metal–Organic Frameworks with Three‐Dimensional Structure

Abstract3D well‐crystallized metal–organic frameworks (MOFs), M‐THBQ (M=Fe, Co, Mn, THBQ=tetrahydroxybenzoquinone), are synthesized and characterized. Their structures are determined as cubic cell in the group of Pm from powder X‐ray diffraction data, and their properties of electronic, magnetic and spectroscopic are also investigated. They are all semiconductors, and Fe‐THBQ exhibits the air‐stable n‐type thermoelectric characteristic as its Seebeck coefficient reaches −130 μV K−1, and the electrical conductivity is 2.7×10−4 S cm−1 at 300 K. Additional, M‐THBQ are paramagnetic, and the value of Weiss constant of Fe‐THBQ is −219.37 K, indicating the existence of robust intramolecular antiferromagnetic exchanges. Meanwhile, they display strong absorption bands in the range of 220 to 1000 nm, suggest M‐THBQ could have the potential to become photoabsorbers, and Fe‐THBQ exhibits a narrow band gap of 0.63 eV according to the ultraviolet absorption edge spectrum.

ZnO Films Obtained by Reactive Magnetron Sputtering: Microstructure, Electrical, and Optical Characteristics

In this study, a technology producing undoped crystalline zinc oxide films with purposefully changed electrical resistance ρ = 3 × 10–4–1 × 107 Ω cm has been developed. The relationship between the electrical characteristics of ZnO layers and the parameters of their deposition has been studied, and the conditions for the formation of high-resistance i-ZnO and low-resistance n-ZnO films with specified values of electrical resistance have been determined. It has been established that the dominant factor determining the conductivity of ZnO films is a change in the concentration of free carriers, controlled by oxygen vacancies. To select the optimal conditions for the formation of highly transparent coatings with a given conductivity, the microstructure and spectral properties (edge absorption and transmission spectra in the transparency region) of n-ZnO films deposited by reactive magnetron sputtering of a zinc target in an argon atmosphere with oxygen (10% Ar, 90% O2) at a pressure of 5 × 10–3 Torr have been studied. It has been shown that the developed method for the discrete formation of ZnO films on amorphous substrates provides stoichiometric crystal structures with a high packing density and spatial orientation of crystallites in the [002] direction. Even in the case of n-ZnO films with ρ = 3 × 10–3 Ω cm, the microstructure causes a high transmittance of the coatings.

Phase transition of InN films via trimethylindium flows

Wurtzite (w) and zincblende (zb) InN films have been grown on (011) SrTiO3 (STO) substrates by metal- organic chemical vapor deposition, the epitaxial relation- ships and optical properties are characterized by X-ray diffraction (XRD), absorption and photoluminescence (PL). Based on XRD θ –2θ and Φ scanning results, the epi- taxial relationships between (w- and zb-) InN films and STO substrates are determined, that is, (0001)[1120]w-InN (011)[100]STO and (100)[011]zb-InN //(011)[100]STO. Compared with the w-InN films, the zb-InN films exhibit a red shift in absorption edge and PL spectra, and a much nar- rower and stronger PL spectrum, implying a better optical quality of zb-InN films. The structure transition is supposed to be due to the difference in atom and bond areal density between the crystal plane of w-InN(0001) and zb-InN(100).

Stability study of organometal halide perovskite and its enhanced X-ray scintillation from the incorporation of anodic TiO2 nanotubes.

Organometal halide perovskite-based optoelectronic devices are currently a hot research area owing to their unique properties, but widespread commercialization is plagued by their poor long-term stability. So far, the degradation mechanism of organometal halide perovskites is still indistinct due to limited real time systematic study. In this work, we in situ study the crystal evolution of an organometal halide perovskite CH3NH3PbI3, which is prepared on different kinds of framework substrates. Based on the in situ grazing incidence X-ray diffraction and X-ray near absorption edge spectrum, we observe the formation of some 2D networks of [PbI6]4− octahedra intermediates during CH3NH3PbI3 degradation in a moist environment at the early step of the degradation mechanism. We also show that the structural stability of CH3NH3PbI3 deposited anodic TiO2 nanotube substrates is relatively better than that of prepared perovskite on TiO2 nanoparticles in moisture. The confinement of the 3D [PbI6]4− octahedral crystal network probability reduces the ion migration by regular pores of crystalline TiO2 nanotubes, improving the stability of the organometal halide perovskite. Furthermore, the X-ray excited luminescence intensity of CH3NH3PbI3 fabricated on TiO2 nanotubes is boosted 88% compared with that of conventional TiO2 nanoparticle substrates, which demonstrates its potential application in scintillation detectors.

Photocatalytic study of methyl orange dye in UV exposure by using ZnO nanoparticles

The ZnO nanoparticles were prepared by mechanical grinding method of the laboratory grade powder. X-ray diffraction (XRD), Transmission electron microscope (TEM), Diffuse reflectance spectra (DRS) characterizations were done for the conformity of phase formation, particle size estimation and optical property study. XRD result shows ZnO nanoparticles are of hexagonal wurzite phase and TEM image shows the diameter and length of the nanoparticles are 59.34 nm and 300 nm respectively. DRS image shows the band edge absorption spectra is coming around 380 nm. The photocatalytic activity was investigated under the UV exposure using laboratory grade ZnO nanoparticles for the decomposition of Methyl Orange (MO) dye. The MO dye decomposition took 60 min for the complete decomposition of dye. The reaction rate and kinetics is also studied. The reaction rate constant is found to be 0.05 min−1 and also it follows pseudo-fast order reaction kinetics. These materials are low cost materials and showing excellent photocatalytic activity.

EXAFS Study of the Local Order in Cu2ZnSn(SxSe1–x)4 Alloys

Local structure in Cu2ZnSn(SxSe1–x)4 alloys is studied by the extended X‐ray absorption fine structure (EXAFS) method. K edge absorption spectra of four elements: Cu, Zn, Sn, and Se have been measured. The EXAFS analysis of the nearest neighbor shell is performed using simultaneous fitting of the data for all four K edges. This provides value of structural parameters in the most consistent way. The cation–anion interatomic distances exhibit the bimodal behavior, i.e., the Me–S and Me–Se distances (Me = Cu, Zn, and Sn) are practically constant over the whole composition range of Cu2ZnSn(SxSe1–x)4 alloys. They are compared to the X‐ray diffraction (XRD) values for these alloys. The analysis of the EXAFS Debye‐Waller factors indicates differences in the static disorder around different cations with the lowest disorder observed in the first coordination shell of Sn atoms.

Analysis of the Optical Properties of Plastically Deformed ZnS(O) Using Band-Anticrossing Theory

The cathodoluminescence and absorption of plastically deformed ZnS(O) single crystals are investigated in the light of band-anticrossing theory. The difference in the oxygen content in the surface layer and in the sample bulk is found using a scanning electron microscope and according to cathodoluminescence data. This fact explains the specifics of the spectral position of the fundamental absorption edge and exciton spectra. The shift dynamics of the bands of self-activated luminescence on deep A centers (SA luminescence) during deformation recrystallization with an increase in the dissolved oxygen concentration is presented. Restriction of the spectral range of the appearance of self-activated luminescence at shallow levels—“edge” luminescence—is established. The nature of the emission bands in the wavelength ranges of 336–350 and 364–390 nm is established. These results refine the energy model of ZnS(O) crystals and can be useful in the case of the practical use of their structure-sensitive properties.

Characterictics of absorption edge of SiO 2 films

Silicon dioxide (SiO2) is one of the most widely used in various optical system as film material. The micro-structure and defects of SiO2 films are of great importance to the functions and performance of these optical systems. In this paper, the absorption edge characteristics of single layer SiO2 films prepared by electron beam evaporation, ion assisted deposition, and magnetron sputtering are investigated in detail via calculating their absorption edge spectrum, which is divided into three regions: the strong absorption, exponential absorption, and weak absorption regions. The bandgap, Urbach tail, and concentration of oxygen deficiency centers (ODC) are obtained by analyzing the measured absorption spectrum. By analyzing the bandgap, Urbach tail, and ODC data of SiO2 films prepared with different deposition techniques and annealed at different temperatures, the atomic arrangement as well as micro-defect information of SiO2 films are obtained and compared. Such information of SiO2 films are important to the preparation of high-performance optical coatings employing SiO2 as the low refractive index material.

Анализ оптических свойств пластически деформированного ZnS(O) с привлечением теории антипересекающихся зон

Abstract The optical properties of plastically deformed ZnS∙0 single crystals have been studied on the basis of bandanticrossing theory. The difference in oxygen concentration in the surface layer and in the bulk of the sample was found from an analysis of the results of cathodoluminescence and scanning electron microscopy. This made it possible to explain the position of the fundamental absorption edge and exciton spectra. Dynamics of the shift of the self-activated luminescence at deep A-centers bands during deformation recrystallization with increasing concentration of dissolved oxygen is shown. The restriction of the spectral range of the appearance of self-activated luminescence at shallow levels is established. The nature of the emission bands in the wavelength range 336-350and 364-390 nm has been discovered. The results can be used both to refine the energy model of ZnS∙O and in the case of practical use of the structure-sensitive properties of zinc sulphide crystals.

Electronic structure of Pr2MnNiO6 from x-ray photoemission, absorption and density functional theory

The electronic structure of double perovskite Pr2MnNiO6 was studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 4+ and 2+ states respectively. Based on charge transfer multiplet analysis of the 2p XPS spectra of both ions, we find charge transfer energies of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ ions reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the ionic values. The partial density of states clearly show a charge transfer character of the system for U − J 2 eV. The O 1s edge absorption spectra reveal a band gap of 0.9 eV, which is close to the value estimated from analysis of Ni and Mn 2p photoemission and absorption spectra. The combined analysis of nature of spectroscopic data and first principles calculations reveal that the material is a p − d type charge transfer insulator with an intermediate covalent character according to the Zannen–Sawatzy–Allen phase diagram.

Samarium doped calcium sulfate ultra-phosphate glasses: Structural, physical and luminescence investigations

Luminescence mechanism of RE doped glasses is significant in optical devices, the glasses of compositions (80-x) P2O5-20CaSO4-(x) Sm2O3 with 0.3 ≤ x ≤ 1.5 mol% have been prepared by melt-quench method. The result of XRD patterns affirmed the amorphous nature of the samples. The structure was investigated successfully using FTIR, NMR and Raman in order to examine the molecular vibrational modes and to verify the de-polymerization process. Absorption and photoluminescence spectra of Sm2O3 doped calcium ultra-phosphate glasses have been reported. Three emission band of Sm3+ centered at 4G5/2→6H9/2 (642 nm), 4G5/2→6H7/2 (597 nm) and 4G5/2→6H5/2 (559 nm) have been observed at λexc = 402 nm. The spectroscopic research reveals the de-polymerization pattern in P2O5 glass structure by conversion of Q3→Q2→Q1 and to Qo units. Physical and optical properties were investigated, doped ions were successfully position at interstice spaces in CSP, the physical properties such as, density, Polarizability, Molar refractivity, and refractive index etc, have been estimated. The absorption spectra in the wavelength range 900–1700 nm were determined, the spectra consist of seven absorption peaks corresponds to transitions from 6H5/2 ground state to excited state. From the absorption edge spectra, the band gap (direct and indirect) and the Urbach energy (ΔE) values were evaluated. The conventional JO (Judd-Ofelt) intensity parameters (Ω2, Ω4 and Ω6) and root mean square (δrms) deviation have been evaluated and discussed with respect to Sm3+ concentration. Obtained result goes along with the Sm3+ doped magnesium zinc sulfo-phosphate glasses for advancement of many functional glasses.

Investigation of the vanadium L23 -edge x-ray absorption spectrum of SrVO3 using configuration interaction calculations: Multiplet, valence, and crystal-field effects

Configuration interaction cluster calculations have been performed to investigate the electronic structure of orthorhombic distorted ${\mathrm{SrVO}}_{3}$ compound, where a considerable tetragonal crystal-field splitting of larger than $180\phantom{\rule{4.pt}{0ex}}\text{meV}$ for ${t}_{2g}$ orbital levels is suggested for the good consistence between the simulated and the experimental spectral line shape. This supports the crystal-field splitting scenario for the metal-insulator transition mechanism. We further calculate V ${L}_{23}$-edge absorption spectra of vanadium oxides with similar ${\mathrm{VO}}_{6}$ octahedral environment for formal $d$ electrons varying from $3{d}^{0}$ to $3{d}^{3}$, where we obtain energy parameters representing the local ground-state properties and provide the theoretical guidance for identifying the chemical valence and the crystal-field strength of a particular vanadium oxide. Our simulated polarization-dependent spectra at different tetragonal crystal-field values reveal a nonlinear orbital-lattice interaction. The orbital polarization $P$ reflecting the electron occupations in different ${d}_{xy}$ and ${d}_{xz(yz)}$ orbital symmetries shows strong sensitivity to small tetragonal crystal field, indicating the strongly correlated electron effect and further addressing the efficiency of strain engineering in functional SVO-based thin films and heterostructures.

Laser processing of transparent semiconductor materials

A proposed method for laser processing of transparent semiconductor materials is based on thermal effect of increasing an absorption of light with a wavelength in the range of fundamental absorption-edge spectrum of the material. In this paper, we provide an analytical and experimental investigation of increase of absorption in semiconductor materials caused by laser radiation with wavelength in the range of absorption-edge of the material.

Simultaneous surface and bulk sensitive XAS measurements of magnetic particle clusters

Magnetic iron oxide nanoparticle clusters (mnpc) coated with organic stabilizers were investigated using scanning transmission x-ray microscopy (STXM). Simultaneous surface and bulk sensitive Fe L3 edge absorption spectra, obtained using a photomultiplier tube and a channeltron, were used to detect subtle changes in the oxidation state in the surface and bulk of Iron Oxide mnpc. The effectiveness of this mode of STXM operation is demonstrated for these nanoparticle clusters.

Electronic structure of FeAl alloy studied by resonant photoemission spectroscopy and Ab initio calculations

Resonant photoemission spectroscopy has been used to investigate the character of Fe 3d states in FeAl alloy. Fe 3d states have two different character, first is of itinerant nature located very close to the Fermi level, and second, is of less itinerant (relatively localized character), located beyond ∼2 eV below the Fermi level. These distinct states are clearly distinguishable in the resonant photoemission data. Comparison between the results obtained from experiments and first principle based electronic structure calculations show that the origin of the itinerant character of the Fe 3d states is due to the ordered B2 structure, whereas the relatively less itinerant (localized) Fe 3d states are from the disorders present in the sample. The exchange splitting of the Fe 3s core level peak confirms the presence of local moment in this system. It is found that the itinerant electrons arise due to the hybridization between Fe 3d and Al 3s and 3p states. Presence of hybridization is observed as a shift in the Al 2p core-level spectra as well as in the X-ray near edge absorption spectra towards lower binding energy. Our photoemission results are thus explained by the co-existence of ordered and disordered phases in the system.