X-ray Photoelectron Valence-band Spectra Research Articles

Quantitative Evaluations on Ozone Evolution Electrocatalysts by Scanning Electrochemical Microscopy for Oxidative Water Treatment.

This study valorized scanning electrochemical microscopy (SECM) for the detection of dissolved O3, which is increasingly in demand for water treatment. Au ultramicroelectrodes biased at 0.62 V RHE provided superior activity and selectivity for O3 reduction, compared to Pt analogues. It allowed quantitative in situ interrogation of ozone evolution reaction (OZER) electrocatalysts with unprecedented estimations on the OZER overpotential. The difference in onset potentials between the OZER and the competing oxygen evolution reaction (OER) primarily accounted for the OZER current efficiency (CE) on boron-doped diamond (BDD, 1.4% at 10 mA cm-2 in 0.5 M H2SO4), Ni-Sb-doped SnO2 (NSS, 10.8%), and SiOx-coated NSS (NSS/SiOx, 34.4%). SECM areal scans in tandem with elemental mapping perspicuously visualized the improved OZER activity by the SiOx overlayer on NSS. A shift in the charge transfer coefficient further rationalized the elevated OZER selectivity on NSS/SiOx, in association with the weakened Sn-O bond strength confirmed by valence band X-ray photoelectron spectra. The invigorated OZER on NSS/SiOx effectively accelerated the degradation of a model aqueous pollutant (4-chlorophenol).

Zinc-doped iron oxide nanostructures for enhanced photocatalytic and antimicrobial applications

A simple, cost-effective method of two-step anodization is used to prepare environmentally benign zinc-doped iron oxide nanostructures for photocatalytic and antimicrobial applications. The effect of zinc doping on the structure and morphology of iron oxide nanostructure is analysed with the help of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy. A detailed analysis of the changes in the binding energy positions of Fe 2p, O 1s, Zn 2p and valence band maximum with variation in doping concentration is carried out with X-ray photoelectron spectroscopy. A combined analysis of valence band X-ray photoelectron spectra and optical reflectance spectra indicates a shift in Fermi level characteristic to a conversion from n-type in pure α-Fe2O3 to p-type in 5-s zinc-doped α-Fe2O3. The room-temperature electrical conductivity of the doped is improved by five orders compared to the undoped nanostructures. The zinc-doped iron oxide nanostructures with p-type conductivity are found to show high photocatalytic degradation efficiency for the organic dye methylene blue. Significant antimicrobial activity is observed with the nanostructures for the microbes Pseudomonas aeruginosa, Bacillus subtilis and E. coli.

Single crystal growth and the electronic structure of Rb2Na(NO3)3: Experiment and theory

Rb2Na(NO3)3 crystals demonstrate nonlinear optical properties and can be used as a converter of laser radiation in the shortwave region. The crystals were grown in the present work by the Bridgman–Stockbarger method in a ratio of 75 ​wt%(RbNO3) and 25 ​wt%(NaNO3). After the growth, a transparent centimeter size single crystal (6 ​cm long) was obtained for the first time that is very important for its practical application. The unit cell volume of double Rb2Na(NO3)3 nitrate is intermediate between the cell volumes of simple rubidium and sodium nitrates, RbNO3 and NaNO3. Electronic structure of Rb2Na(NO3)3 was studied in the present work from both experimental and theoretical viewpoints. In particular, employing X-ray photoelectron spectroscopy, we have measured binding energies of core electrons and energy distribution of the electronic states within the valence band region of the Rb2Na(NO3)3 crystal and established rather big binding energies for N 1s and O 1s core-level electrons. The bombardment of middle-energy Ar+ ions induces transformation of some nitrogen atoms of the analyzing topmost layers of the Rb2Na(NO3)3 crystal surface from the NO3– group to the NO2– group. To explore in detail the filling of the valence band of Rb2Na(NO3)3 by electronic states associated with constituting atoms, we use first-principles calculations within a density functional theory (DFT) framework. The DFT calculations reveal that O 2p states are the principal contributors to the valence band bringing the main input in its upper portion. The theoretical finding is supported experimentally by fitting the X-ray photoelectron valence band spectrum and the X-ray emission O Kα band on the total energy scale. The conduction band bottom of Rb2Na(NO3)3 is composed by unoccupied O 2p and N 2p states in almost equal proportion.

Determination of sp2 and sp3 phase fractions on the surface of diamond films from C1s, valence band X-ray photoelectron spectra and CKVV X-ray-excited Auger spectra

The practice of applying the methods for determining the relative contents of carbon atoms in sp2 and sp3 hybridization states from the profiles of C1s X-ray photoelectron and carbon KVV (CKVV) Auger spectra is analyzed. Difficulties in using C1s and CKVV spectra for determining the sp2/sp3 ratios are discussed. A method is proposed for evaluating the fractions of sp2 and sp3 phases based on the fitting of the valence band X-ray photoelectron spectra by superposition of valence band spectra of samples with carbon atoms in pure sp2 and sp3 states. Relative fractions of sp2 and sp3 phases on the virgin surfaces of two ultrananocrystalline diamond films, and on their surfaces subjected to friction, were determined using C1s spectra, CKVV Auger spectra, and valence band spectra. All three methods gave the results that are consistent for virgin film surfaces with accuracy of 2%, and for the surfaces of films subjected to friction, 15%. In contrast to the ultrananocrystalline films, three XPS-based methods applied to a microcrystalline diamond film yielded significantly different sp2/sp3 ratios. The reasons for this discrepancy are shown to lie in different analysis depths of these methods, and in different morphology of the film surfaces.

Experimental determination of electron attenuation lengths in complex materials by means of epitaxial film growth: Advantages and challenges

Accurate electron attenuation lengths are of critical importance in using electron spectroscopic methods to quantitatively characterize complex materials. Here, the authors show that analysis of core-level and valence-band x-ray photoelectron spectra excited with monochromatic AlKα x-rays from the substrate and measured as a function of film thickness can be used to determine electron attenuation lengths in epitaxial SrTiO3 films on Ge(001). Closely lattice-matched epitaxial heterojunctions are ideal systems for determining attenuation lengths provided the films grow in a layer-by-layer fashion, leading to atomically flat surfaces, and the buried interfaces are atomically abrupt. In principle, either the rate of attenuation of substrate peak intensities or the rate of increase of film peak intensities can be used for this purpose. However, the authors find that structural nonuniformities in the films reduce the accuracy of electron attenuation lengths determined from photoelectrons that originate within the films. A more reliable source of information is found in photoelectrons from the substrate which traverse the film. By using the energy dependence of calculated electron attenuation lengths from the NIST database in combination with Ge 3d core and Ge-derived valence-band intensities, the authors determine electron attenuation length as a function of kinetic energy for SrTiO3.

Aluminium doping in iron oxide nanoporous structures to tailor material properties for photocatalytic applications

In this study, metal doping of iron oxide nanostructures grown by anodization is successfully achieved by the simple cost effective technique of electrochemical doping. Structural and morphological characterizations of all the samples are done using X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy in conjunction with field-emission scanning electron microscopy, respectively. A detailed analysis of the X-ray photoelectron spectra is done for all the samples to obtain the effect of aluminium doping on the multiplet peak positions of Fe 2p and different species of oxygen. Analysis of the valence band X-ray photoelectron spectra (VB XPS) reveals a displacement of ‘valence band edge’ towards higher energy on doping. The VB XPS coupled with optical data is used for evaluating the shift in the Fermi level towards the conduction band minimum, which indicates the formation of donor defect level on doping. The reduction in band gap from 1.96 to 1.72 eV and enhanced electrical conductivity on doping are observed to produce an improvement in the photo catalytic activity for aluminium-doped nanostructures compared to undoped.

Band bending at the ZnO(0001)-Zn surface produced by electropositive, electronegative and atmospheric adsorbates

We have analysed the surface band bending (SBB) at the clean ZnO(0001)-Zn surface and after its modification by electropositive, electronegative and atmospheric adsorbates. The evolution of the band bending with increasing adsorption was monitored by measuring core-level and valence-band X-ray photoelectron spectra. We found that the SBB produced by the adsorption of electropositive elements was always downwards, reaching in all cases the limit imposed by the crossing of the conduction-band minimum with the Fermi level. The adsorption of electronegative elements produced always upward band bending, but in this case a pinning of the SBB was observed that kept the valence-band maximum far from the Fermi level. A self-consistent equation relating the adsorbate level occupation with the band bending is shown to qualitatively reproduce the observed SBB pinning effect. In contrary to the commonly assumed upwards SBB for the ZnO/air interface, a downward SBB was observed after exposing the clean surface to atmospheric air. A downward SBB was also observed when the surface was bombarded with 1 keV Ar+ in vacuum.

Photocatalytic hydrogen evolution on P-type tetragonal zircon BiVO4

Tetragonal zircon BiVO4 (P-BiVO4) were grown on fluorine-doped tin oxide (FTO) glass via hydrothermal method. The cathodic photocurrent and Mott-Schottky analysis indicate that the tetragonal zircon BiVO4 is a p-type semiconductor. Inductively coupled plasma (ICP) analysis and X-ray photoelectron spectrum showed that there are Bi vacancies and interstitial oxygen exist in the crystal, which are the origin of the p-type conductivity. The flat band potential of the P-BiVO4 is about 1.33 V (vs Ag/AgCl) inferred from Mott-Schottky plots. Combining with diffuse reflection spectrum and valence band X-ray photoelectron spectrum, the calculated conduction band value of the P-BiVO4 is about 0.06 V vs RHE, slightly higher than the reduction potential of hydrogen. However, the P-BiVO4 exhibit hydrogen production activity under Xe light irradiation even though its conduction band level is not negative enough. This can be attributed to the hot carrier processes in p-type semiconductors.

DFT calculations of energy dependent XPS valence band spectra

In the past few years it became regularly possible to measure valence band X-ray photoelectron spectra (XPS) using variable excitation energies. This ranges from UV-light to conventional X-ray sources (like Al Kα) all the way to synchrotron radiation with energies of several keV. In order to explain the observed variations in intensity with respect to the excitation energy, we performed XPS calculations using the WIEN2k code. The new PES module computes the XPS spectra using a combination of partial density of states times excitation-energy-dependent atomic-orbital cross sections. It considers as additional correction the charge fraction of the corresponding orbital located inside the atomic spheres. The resulting XPS spectra are compared with experimental data for SiO2, PbO2, CeVO4, In2O3 and ZnO at different excitation energies and in general good agreement between the simulated and experimental spectra has been achieved. In some cases significant unexpected contributions like Pb-6d in PbO2 or Zn-4p in ZnO appear and explain some features in the experimental spectra which previously have not been identified.

Ultra-trace (parts per million-ppm) W6+ dopant ions induced anatase to rutile transition (ART) of phase pure anatase TiO2 nanoparticles for highly efficient visible light-active photocatalytic degradation of organic pollutants

A series of novel photocatalysts were synthesized by incorporating tungsten (W6+) ions in to the lattice of pure anatase TiO2 nanoparticles with ultra-trace concentrations (ppm) such as 10 ppm, 50 ppm, 90 ppm and 120 ppm using a simple one-step hydrothermal method under identical conditions. X-ray diffraction (XRD) studies, revealed a spectacular structural phase transformation from anatase to rutile on doping and associated morphological changes are seen by scanning electron microscopy (SEM). The phase transformation is promoted with the increase of W concentration up to 50 ppm and inhibited thereafter. Microstructural lattice distortions due to the presence of W6+ ions are monitored by high-resolution transmission electron microscopy (HR-TEM). The valence band X-ray photoelectron spectra (XPS), Ultraviolet photoelectron spectra (UPS) and UV–Vis absorption studies confirm the reduction of band gap for W doped TiO2 mixed phase nanoparticles. The doping causes an enhanced visible light absorption. Room temperature photoluminescence (PL) spectroscopy ensures an oxygen vacancy mediated phase transformation. The photocatalytic performances of the W doped TiO2 catalysts are evaluated for the degradation of Rhodamine B (RhB), Methylene blue (MB) and Methyl orange (MO) aqueous solutions under visible-light irradiation. The efficiency of photocatalytic degradation of the dyes gradually increased with the content of W6+ ions (till 50 ppm) and then decreased which is consistent with the structural and optical studies. The control experiments, showed possible oxidative species, are hydroxyl (·OH-) and oxygen (·O2-) radicals while the earlier plays a dominant role. The resuability tests performed for five cycles demonstrate high stability and reusability of the photocatalysts. A possible synergistic mechanism based on the impurity energy levels of W6+ ions, oxygen vacancies and anatase-rutile heterojunction for the enhancement of the photocatalytic activity under visible-light irradiation is proposed.

Electronic structure and optical properties of LiGa0.5In0.5Se2 single crystal, a nonlinear optical mid-IR material

Measurements of X-ray photoelectron core-level and valence-band spectra for pristine and irradiated with Ar+ ions surfaces of LiGa0.5In0.5Se2 single crystal, novel nonlinear optical mid-IR selenide grown by a modified vertical Bridgman-Stockbarger technique, are reported. Electronic structure of LiGa0.5In0.5Se2 is elucidated from theoretical and experimental points of view. Notably, total and partial densities of states (DOSs) of the LiGa0.5In0.5Se2 compound are calculated based on density functional theory (DFT) using the augmented plane wave + local orbitals (APW + lo) method. In accordance with the DFT calculations, the principal contributors to the valence band are the Se 4p states, making the main input at the top and in the upper part of the band, while its bottom is dominated by contributions of the valence s states associated with Ga and In atoms. The theoretical total DOS curve peculiarities are found to be in excellent agreement with the shape of the X-ray photoelectron valence-band spectrum of the LiGa0.5In0.5Se2 single crystal. The bottom of the conduction band of LiGa0.5In0.5Se2 is formed mainly by contributions of the unoccupied Ga 4s and In 5s states in almost equal proportion, with somewhat smaller contributions of the unoccupied Se 4p states as well. Our calculations indicate that the LiGa0.5In0.5Se2 compound is a direct gap semiconductor. The principal optical constants of LiGa0.5In0.5Se2 are calculated in the present work.

Effect of reaction atmosphere on photodeposition of Pt nanoparticles and photocatalytic hydrogen evolution from SrTiO3 suspension system

We systematically investigated the impact of reaction atmosphere on the Pt cocatalyst photodeposition and hydrogen evolution. A long induction period which is hardly found in close-system appears in the presence of oxygen, and is affected by the concentration of chloroplatinic acid. The Pt cocatalyst is metal state and contributes to the electronic states near Fermi level judging from the valence band X-ray photoelectron spectrum. The cocatalyst metal Pt will reduce the surface photovoltage signals due to the metal feature. The hydrogen evolution rate increased and reached a platform with increasing the Pt coverage on the surface of photocatalyst which is characterized by the Pt:Ti atomic ratio.

AgGaSiSe4: Growth, crystal and band electronic structure, optoelectronic and piezoelectric properties

Growth of AgGaSiSe4 single crystals, determination of their crystal structure, studies of electronic structure and optical properties are presented. The X-ray photoelectron core-level and valence-band spectra were measured. We recorded the X-ray emission Se Kβ2 and Ga Kβ2 bands, giving information on the energy distribution of the Se4p and Ga4p states, respectively, and compared with the X-ray photoelectron valence-band spectrum. The main contributions of the Se4p and Ga4p states have been found in the upper and central parts of the valence band, respectively, with their substantive contributions in other parts of the band. The spectral distribution of the absorption coefficient in the temperature range 100–300K was investigated and band gap variation coefficient was evaluated (dEg/dT=−4.5×10−4eV/K). The activation energies of dark conductivity were calculated as follows: Ea1=0.03eV, Ea2=0.24eV. The IR transmission curve and the relaxation kinetics of photoinduced piezoelectric module were described.

Phase quantification by X-ray photoemission valence band analysis applied to mixed phase TiO2 powders

A method of quantitative phase analysis using valence band X-ray photoelectron spectra is presented and applied to the analysis of TiO2 anatase-rutile mixtures. The valence band spectra of pure TiO2 polymorphs were measured, and these spectral shapes used to fit valence band spectra from mixed phase samples. Given the surface sensitive nature of the technique, this yields a surface phase fraction. Mixed phase samples were prepared from high and low surface area anatase and rutile powders. In the samples studied here, the surface phase fraction of anatase was found to be linearly correlated with photocatalytic activity of the mixed phase samples, even for samples with very different anatase and rutile surface areas. We apply this method to determine the surface phase fraction of P25 powder. This method may be applied to other systems where a surface phase fraction is an important characteristic.

Single Silver Adatoms on Nanostructured Manganese Oxide Surfaces: Boosting Oxygen Activation for Benzene Abatement.

The involvement of a great amount of active oxygen species is a crucial requirement for catalytic oxidation of benzene, because complete mineralization of one benzene molecule needs 15 oxygen atoms. Here, we disperse single silver adatoms on nanostructured hollandite manganese oxide (HMO) surfaces by using a thermal diffusion method. The single-atom silver catalyst (Ag1/HMO) shows high catalytic activity in benzene oxidation, and 100% conversion is achieved at 220 °C at a high space velocity of 23 000 h-1. The Mars-van Krevelen mechanism is valid in our case as the reaction orders for both benzene and O2 approach one, according to reaction kinetics data. Data from H2 temperature-programmed reduction and O core-level X-ray photoelectron spectra (XPS) reveal that Ag1/HMO possesses a great amount of active surface lattice oxygen available for benzene oxidation. Valence-band XPS and density functional theoretical calculations demonstrate that the single Ag adatoms have the upshifted 4d orbitals, thus facilitating the activation of gaseous oxygen. Therefore, the excellent activation abilities of Ag1/HMO toward both surface lattice oxygen and gaseous oxygen account for its high catalytic activity in benzene oxidation. This work may assist with the rational design of efficient metal-oxide catalysts for the abatement of volatile organic compounds such as benzene.

Synthesis, structural, electronic and linear electro-optical features of new quaternary Ag2Ga2SiS6 compound

For the first time phase equilibria and phase diagram of the AgGaS2–SiS2 system were successfully explored by differential thermal and X-ray phase analysis methods. Crystal structure of low-temperature (LT) modification of Ag2Ga2SiS6 (LТ- Ag2Ga2SiS6) was studied by X-ray powder method and it belongs to tetragonal space group I-42d, with unit cell parameters a=5.7164(4) Å, c=9.8023(7) Å, V=320.32(7) Å3. Additional details regarding the crystal structure exploration are available at the web page Fachinformationszentrum Karlsruhe. X-ray photoelectron core-level and valence-band spectra were measured for pristine LТ- Ag2Ga2SiS6 crystal surface. In addition, the X-ray photoelectron valence-band spectrum of LТ-Ag2Ga2SiS6 was matched on a common energy scale with the X-ray emission S Kβ1,3 and Ga Kβ2 bands, which give information on the energy distribution of the S 3p and Ga 4p states, respectively. The presented X-ray spectroscopy results indicate that the valence S p and Ga p atomic states contribute mainly to the upper and central parts of the valence band of LТ-Ag2Ga2SiS6, respectively, with a less significant contribution also to other valence-band regions. Band gap energy was estimated by measuring the quantum energy in the spectral range of the fundamental absorption. We have found that energy gap Eg is equal to 2.35eV at 300K. LT-Ag2Ga2SiS6 is a photosensitive material and reveals two spectral maxima on the curve of spectral photoconductivity spectra at λmax1 =590nm and λmax2 =860nm. Additionally, linear electro-optical effect of LT-Ag2Ga2SiS6 for the wavelengths of a cw He-Ne laser at 1150nm was explored.

Electronic structure of single-crystal solid solutions Pb1-xBaxTiO3 (0 ≤ x ≤ 1) from X-ray photoelectron spectroscopy and real-space multiple electron scattering calculations

Valence band and core level X-ray photoelectron spectra (XPS) are measured in single-crystal solid solutions Pb1-xBaxTiO3 (x = 0, 0.021, 0.146, 0.24, 0.541, 0.784, 0.906, 1). Valence band densities of states (DOS) and theoretical valence band XPS are calculated for Pb1-xBaxTiO3 (x = 0, 0.12, 0.25, 0.5, 0.875, 1) via the method of multiple electron scattering in real space. Experimental and theoretical valence band XPS are in good agreement. The increase of ionicity of the TiO bonds in Pb1-xBaxTiO3 upon the growth of relative Ba content x is predicted theoretically and shown experimentally using the energy position of the charge transfer satellites in the Ti2p XPS. The increase of Ti2p-spectrum line widths against relative Ba content x is observed.

Band Gap Engineering of Wurtzite-Type Narrow Band Gap Oxide Semiconductor β-CuGaO2

β-CuGaO2 is an oxide semiconductor possessing wurtzite-derived β-NaFeO2 structure. Its band gap is 1.47 eV in near-infrared region, and the first principles calculation indicates that it is a direct band gap semiconductor. Therefore, this material is expected to be applicable to optoelectronic devices working in near-infrared region. When the band gap of β-CuGaO2 is widened into visible region, the material is expected to be applicable to visible LEDs and lasers, photocatalyst and so on. In the present study, we demonstrated band gap engineering of β-CuGaO2 by alloying with β-CuAlO2 and β-LiGaO2 possessing wurtzite-derived β-NaFeO2 structure in order to widen the band gap. Cu(Ga1-xAlx)O2 alloys were prepared by ion-exchange of Na+ ions in β-Na(Ga1-xAlx)O2 with Cu+ ions in CuCl at 250 °C for 48 h under vacuum. (Cu1-xLix)GaO2 alloys were prepared by ion-exchange of Cu+ ions in β-CuGaO2 with Li+ ions in LiCl at 300 °C for 48 h under vacuum. Wurtzite-type β-phases were obtained in 0≤x≤0.7 for Cu(Ga1-xAlx)O2 system and in 0≤x≤1 for (Cu1-xLix)GaO2 system. In β-Cu(Ga1-xAlx)O2, the optical band gap increased linearly with the increasing alloying level; no band gap bowing appeared in the present system. The band gap of β-CuGaO2 was widened up to 2.1 eV at β-Cu(Ga0.3Al0.7)O2; this energy corresponds to red light. In β-(Cu1-xLix)GaO2, the energy band gap increased almost linearly with the increasing alloying level up to x~0.9; the largest band gap in this composition range was 3.0 eV corresponding to violet light at β-(Cu0.11Li0.89)GaO2. When the alloying level increased further, the band gap steeply increased from 3.0 eV at x=0.89 to 5.6 eV at x=1. The valence band X-ray photoelectron spectra of β-(Cu1-xLix)GaO2 indicated that the steep increase in energy band gap from x~0.9 to 1 is attributed to that the Cu 3d contribution around the top of the valence band electronic states vanishes for the alloys with x>0.9. These results indicate that the energy band gap of β-CuGaO2 is highly controllable in the wavelength region from near-infrared to entire visible lights. Thus, it is expected that β-CuGaO2 opens new applications of oxide semiconductors in devices working in visible region.

Probing the charge separation process on In2S3/Pt-TiO2 nanocomposites for boosted visible-light photocatalytic hydrogen production

A simple refluxing wet-chemical approach is employed for fabricating In2S3/Pt-TiO2 heterogeneous catalysts for hydrogen generation under visible light irradiation. When the mass ratio between Pt-TiO2 and cubic-phased In2S3 (denoted as In2S3/Pt-TiO2) is two, the composite catalyst shows the highest hydrogen production, which exhibits an 82-fold enhancement over in-situ deposited Pt-In2S3. UV–vis diffuse reflectance and valence band X-ray photoelectron spectra elucidate that the conduction band of In2S3 is 0.3eV more negative compared to that of TiO2, favouring charge separation in the nanocomposites. Photoelectrochemical transient photo-current measurements and optical pump – terahertz probe spectroscopic studies further corroborate the charge separation in In2S3/Pt-TiO2. The migration of photo-induced electrons from the In2S3 conduction band to the TiO2 conduction band and subsequently into the Pt nanoparticles is found to occur within 5ps. Based on the experimental evidence, a charge separation process is proposed which accounts for the enhanced activity exhibited by the In2S3/Pt-TiO2 composite catalysts.

Specific features of the electronic structure and optical properties of KPb2Br5: DFT calculations and X-ray spectroscopy measurements

Density functional theory (DFT) calculations are made in order to explore the total and partial densities of states of potassium dilead pentabromide, KPb2Br5, by using the augmented plane wave+local orbitals (APW+lo) method as incorporated in the WIEN2k package. The present calculations reveal that the principle contributors to the valence band of KPb2Br5 are the Pb 6s and Br 4p states contributing predominantly at the bottom and at the top of the band, respectively, while the bottom of the conduction band is formed mainly from contributions of the unoccupied Pb 6p states. The curves of total density of states derived by the present DFT calculations of KPb2Br5 are found to be in agreement with the experimental X-ray photoelectron valence-band spectrum of the compound studied. Comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the valence Br p and K s states and the X-ray photoelectron valence-band spectrum of the KPb2Br5 single crystal indicate that the Br 4p and K 4s states contribute mainly at the top and in the upper portion of the valence band, respectively, being in agreement with data of the present DFT band-structure calculations of this compound. Principal optical characteristics of KPb2Br5, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are also studied by the DFT calculations.