F−, Cl−, Li+ and Na+ adsorption on AlN nanotube surface: A DFT study

Adsorption of two anions (F⁻ and Cl⁻) and two cations (Li⁺ and Na⁺) on the surface of aluminum nitride nanotubes (AlNNTs) is investigated by density functional theory. The reactions are site-selective, so that the cations and anions prefer to be adsorbed atop the N and Al atoms of the tube surface, respectively. The adsorption energies of anions (−4.46 eV for F⁻ and −1.12 eV for Cl⁻) are much higher than those of cations (about −0.17 eV for Li⁺ and −0.12 eV for Na⁺) which can be explained using frontier molecular orbital theory. It was found that the adsorption of anions may facilitate the electron emission from the AlNNT surface by reducing the work function due to the charge transfer occurs from the anions to the tube. It has been predicted that in contrast to the cations the adsorption of anions also obviously increases the electrical conductivity of AlNNT.     

Ion beam induced reaction of carbon films on Si(1 0 0)

The irradiation effects of 2 MeV He⁺ and Ar⁺ ions on the film structure of the C–Si system were investigated with RHEED and XPS. The formation of SiC phase and/or the growth of epitaxial SiC were possible by He⁺ irradiation for the carbon films up to 0.7 nm in thickness, which was thinner than that by Ar⁺ irradiation. The He⁺ irradiation could not grow the turbostratic graphite which could be grown by Ar⁺ irradiation. The mechanism of the formation and the epitaxial growth of SiC by ion irradiation was discussed from the view point of the energy transfer from the irradiated ions.     

Radioluminescence of synthetic quartz related to alkali ions

The radioluminescence (RL) of synthetic quartzes (GEMMA Quartz & Crystal Company) has been measured at room temperature. Some samples were treated by electrodiffusion (“sweeping”) in order to change the concentrations of alkali ions, mainly Li⁺ and Na⁺, which in quartz are known to be linked to Al ions, substitutional for Si ions.The RL emission spectra show evidence of a role of alkali ions in affecting some specific emissions. All the spectra could be analysed as composed of four bands in the blue and UV region. Specifically, the well known blue emission at around 470 nm was seen to be composed by two bands at 430 nm (2.86 eV) and at 485 nm (2.53 eV). Effects of irradiation, during the RL measurements, were clearly seen only in the “Li swept in” sample, namely an increase in the 485 nm band intensity and a decrease in the 430 nm band one. The previously reported UV emission was detected at 355 nm (3.44 eV) in all the samples, being the most intense band in the “swept out” sample. A further UV emission was detected at 315 nm (3.94 eV), more intense in untreated samples.Possible assignments of the detected emission bands are discussed in relation to the defects of quartz, specifically focusing on the Al centres that are most affected by sweeping procedures.     

Conductometric study of complex formations between some substituted pyrimidines and some metal ions in acetonitrile and the determination of thermodynamic parameters

The complexation reactions between Cr³⁺, Cd²⁺, Co²⁺, Ni²⁺, Hg²⁺, Zn²⁺, Pb²⁺,and Ag⁺ metal ions with diethyl-3-(4-hydroxy-6-methylpyrimidin-2-yl) guanidine (L1), 2-amino,4-hydroxy,6-methylpyrimidine (L2), and 2-(diethylamin),4-hydroxy,6-methylpyrimidine (L3) in acetonitrile (AN) were studied using a conductometric method. The formation constants of the resulting complexes were determined from computer fitting conductance-mole ratio data. The results revealed that the formation constants of L1 with metal ions are varying in order of Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Hg²⁺ > Ag⁺ ~ Cd²⁺ > Ni²⁺. For L2 and L3 the sequence of complex formation constants are follow as Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Cd²⁺ > Hg²⁺ > Ag⁺ > Ni²⁺ and Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺ ~ Hg²⁺ ~ Cd²⁺ ~ Ag⁺, respectively. The values of the thermodynamic parameters (ΔH, ΔS and ΔG) for complexation reactions were obtained from the temperature dependence of the stability constants. In all cases, the complexes were found to be enthalpy stabilized but entropy destabilized. In addition, some ab-initio quantum-mechanical calculations were carried out, in order to obtain a clue about the degree tendency of ligands to metal ions.     

Measurement of the sputter yield after mild ion erosion of a pristine Cu(001) surface

Using the STM technique we have determined the sputter yield on a pristine Cu(001) surface after mild (fluence less than 0.044 ions per surface atom) bombardment of the pristine surface with 800 eV Ar⁺ions at normal incidence. The experiments have been performed at substrate temperatures ranging from 200 to 350 K. Making use of the positional correlation of adatoms and surface vacancies, at 200 K and 325 K, we concluded that about 1/3 of the surface adatoms originate from interstitials arriving at the surface and they give a direct indication of the buried bulk vacancies. A careful analysis of the different areas for surface vacancies and adatom then allowed a quantitative evaluation of the sputter yield at 1.2 Cu atoms per 800 eV Ar⁺ ion.     

Combined XPS,electrochemical and Kelvin probe measurements of NaY zeolite

In the present study X-ray Photoelectron Spectroscopy (XPS) combined with in situ electrochemical and Kelvin probe measurements was used in order to get a deeper insight on the mechanism of the cation transport through NaY zeolite and the charge transfer through the Au electrode/zeolite interface. It is shown that by imposing a potential gradient across the NaY powder which is sandwiched between two electrodes, Na⁺ ions can be electrically transferred to or from the Au working electrode area, following the direction of the applied potential between the two electrodes. Two peaks corresponding to sodium species were detected by means of in situ XPS investigation during potential application. The first peak of Na1s photoelectrons with binding energy at 1072.2 ± 0.2 eV is attributed to Na adsorbed on the grounded Au electrode with its coverage remaining unchanged upon potential imposition. The second peak is directly associated with Na present in the zeolite and upon potential application its binding energy varies proportionally with the variation of the surface potential measured by Kelvin probe. Upon varying the potential from − 4 to + 4 V between the working and counter electrode, the Na⁺ concentration decreases by ca30% at the Au/zeolite interface. However the invariant amount of Na on the Au electrode under vacuum shows that the variation in Na⁺ concentration is not due to ionic transfer onto the Au surface but instead Na⁺ accumulation can be assumed at the Au/zeolite interface. On the other hand, current or potential application under O₂ atmosphere promotes the electrocatalytic reaction of Na⁺ towards the formation of Na₂O on the Au electrode surface.     

Electronic excitations and luminescence of SrAlF5 crystals doped with Ce3+ ions

This paper reports the results of a time-resolved photoluminescence and energy transfer processes study in Ce³⁺ doped SrAlF₅ single crystals. Several Ce³⁺ centers emitting near 4 eV due to 5d-4f transitions of Ce³⁺ ions substituting for Sr²⁺ in non-equivalent lattice sites were identified. The lifetime of these transitions is in the range of 25–35 ns under intra-center excitation in the energy region of 4–7 eV at T = 10 K. An effective energy transfer from lattice defects to dopant ions was revealed in the – 7–11 eV energy range. Both direct and indirect excitation channels are efficient at room temperature. Excitons bound to dopants are revealed at T = 10 K under excitation in the fundamental absorption region above 11 eV, as well as radiative decay of self-trapped excitons resulting in luminescence near 3 eV.     

M/Li+(M = Mg2+, Zn2+, and Mn2+) ion-exchange on lithium ion-conducting perovskite-type oxides and their properties

Lithium ions of perovskite-type lithium ion conductor La_0.55Li_0.35TiO₃ were replaced by divalent Mg²⁺, Zn²⁺, and Mn²⁺ ions in an ion-exchange reaction using molten chlorides. The polycrystalline Mg-exchanged and Zn-exchanged samples are solid electrolytes for divalent Mg²⁺ and Zn²⁺ ions, whose dc ionic conductivities (σ = 2.0 × 10^− 6 S cm^− 1 at 558 K for the Mg-exchanged sample, La_0.56(2)Li_0.02(1)Mg_0.16(1)TiO_3.01(2) and σ = 1.7 × 10^− 6 S cm^− 1 at 708 K for the Zn-exchanged samples, La_0.55(1)Li_0.0037(2)Zn_0.15(1)TiO_2.98(2)) were compared to those of the known highest Mg²⁺ and Zn²⁺ inorganic solid electrolytes. The Mn-exchanged sample, then, showed paramagnetic behavior in the temperature range of 2 to 300 K. The Mn ions in the exchanged sample are divalent and the spin configuration is in high spin state (S = 5/2).     

Ultraviolet spectroscopy of Pr+3 and its use in making ultraviolet filters

Sputtered deposited thin films of AlN:Pr and GaN:Pr emit in ultraviolet–visible and visible regions of the spectrum, respectively, under electron excitation in cathodoluminescence apparatus. The goal is to study the ultraviolet emission from Pr⁺³ when doped in nitride semiconductor hosts. Luminescence peaks at a wavelength of 295 nm (4.2 eV), 335 nm (3.7 eV) and 385 nm (3.24 eV) are observed as a result from ¹S₀ → ¹G₄, ¹S₀ → ¹D₂ and ¹S₀ → ¹I₆ transitions, respectively. However the ¹S₀ → ¹G₄ and ¹S₀ → ¹D₂ transitions are not observed when Pr⁺³ is doped in GaN host. The bandgap of GaN absorbs the ultraviolet radiation emitted from Pr⁺³ and hence GaN can be used as ultraviolet filter for radiation shielding and protection purposes. AlN is transparent to ultraviolet due to its wide bandgap of 6.2 eV.     

Structural,ferroelectric, optical properties of A-site-modified Bi0.5(Na0.78K0.22)0.5Ti0.97Zr0.03O3 lead-free piezoceramics

We reported the role of A-site modification on the structural, ferroelectric, optical and electrical field-induced strain properties of Bi_0.5(Na_0.78K_0.22)_0.5Ti_0.97Zr_0.03O₃ lead-free piezoceramics. The Li⁺ ions with concentration from 0 to 5 mol% were used to substitute at A-site. There was no phase transition when Li⁺ ions was added up to 5 mol%. The electric field-induced strain (S_max/E_max) values increased from 600 to 643 pm/V for 2 mol% Li⁺-added which results from distortion both rhombohedral and tetragonal phase structures. The band gap reduced from 2.88 to 2.68 eV and the saturation polarization decreased from 46.2 to 26.1 μC/cm² when Li⁺ ions concentration increased from 0 to 5 mol% respectively. We expect that this work could be helpful for further understanding the role of A-site dopants in comparison with B-site modification in lead-free Bi_0.5(Na,K)_0.5TiO₃-based ceramics.     

Franck–Hertz effect in cathodo- and photoluminescence of wide-gap materials

A brief overview of previously obtained and novel data on the manifestations of an analogue of Franck–Hertz effect in photo- and cathodoluminescence of wide-gap inorganic materials is presented. On the example of NaCl:Tl⁺ and MgO:Cr³⁺ single crystals, the excitation processes of the luminescence of 6s² Tl⁺ ions and 3d³ Cr³⁺ ions by 5–15 keV electrons or 5–20 eV photons at 6–420 K have been studied. The rapid processes of the direct energy transfer to Tl⁺ by hot conduction electrons or to Cr³⁺ centers by hot electrons and/or hot valence holes have been separated from rapid excitonic and more inertial electron–hole processes.     

Reduction of thin-film ceria on Pt(111) by supported Pd nanoparticles probed with resonant photoemission

Local defects present in CeO_2 ? x films result in a mixture of Ce³⁺ and Ce⁴⁺ oxidation states. Previous studies of the Ce 3d region with XPS have shown that depositing metal nanoparticles on ceria films causes further reduction, with an increase in Ce³⁺ concentration. Here, we compare the use of XPS and resonant photoemission spectroscopy (RESPES) to estimate the concentration of Ce³⁺ and Ce⁴⁺ in CeO_2 ? x films grown on Pt (111), and the variation of this concentration as a function of Pd deposition. Due to the nature of the electronic structure of CeO_2 ? x, resonant peaks are observed for the 4d–4f transitions when the photon energy matches the resonant energy; (hν = 121.0 eV) for Ce³⁺ and (hν = 124.5 eV) for Ce⁴⁺. This results in two discrete resonant photoemission peaks in valence band spectra. The ratio of the difference of these peaks with off-resonance scans gives an indication of the relative contribution of Ce³⁺. Results from RESPES indicate reduction of CeO_2 ? x on deposition of Pd, confirming earlier findings from XPS studies.     

Synthesis and luminescence properties of Gd6MoO12:Yb3+, Er3+ phosphor with enhanced photoluminescence by Li+ doping

Yb³⁺/Er³⁺ co-doped Gd₆MoO₁₂ and Yb³⁺/Er³⁺/Li⁺ tri-doped Gd₆MoO₁₂ phosphors were prepared by adjusting the annealing temperature via the high temperature solid-state method. Under the excitation of 980 nm semiconductor, the upconversion luminescence properties were investigated and discussed. In the experimental process, we get the optimum Yb³⁺ concentration and the concentration quench effect will happen while the concentration extends the given region. According to the Yb³⁺ concentration quenching effects, the critical distance between Yb³⁺ ions had been calculated. The measured UC luminescence exhibited a strong red emission near 660 nm and green emission at 530 nm and 550 nm, which are due to the transitions of Er³⁺(⁴F_9/2, ²H_11/2, ⁴S_3/2) → Er³⁺(⁴I_15/2). Then the effect of excitation power density in different regions on the upconversion mechanisms was investigated and the calculated results demonstrate that the green and red upconversion is a two-photon process. A possible mechanism was discussed. After Li⁺ ions mixing, the upconversion emission enhanced largely, and the optimum Li⁺ concentration was obtained while fixed the Yb³⁺ and Er³⁺ on the above optimum concentration. This enhancement owns to the decrease of the local symmetry around Er³⁺ after Li⁺ ions doping into the system. This result indicates that Li⁺ is a promising candidate for improving luminescence in some case.     

Li3+ ion irradiation effects on ionic conduction in P(VDF–HFP)–(PC + DEC)–LiClO4 gel polymer electrolyte system

Swift heavy ion irradiation of P(VDF–HFP)–(PC + DEC)–LiClO₄ gel polymer electrolyte system with 48 MeV Li³⁺ ions having five different fluences was investigated with a view to increase the Li⁺ ion diffusivity in the electrolyte. Irradiation with swift heavy ion (SHI) shows enhancement of conductivity at lower fluences and decrease in conductivity at higher fluences with respect to unirradiated polymer electrolyte films. Maximum room temperature (303 K) ionic conductivity is found to be 2.2 × 10^− 2 S/cm after irradiation with fluence of 10¹¹ ions/cm². This interesting result could be ascribed to the fluence-dependent change in porosity and to the fact that for a particular ion beam with a given energy higher fluence provides critical activation energy for cross-linking and crystallization to occur, which results in the decrease in ionic conductivity. The XRD results show decrease in the degree of crystallinity upon ion irradiation at low fluences (≤ 10¹¹ ions/cm²) and increase in crystallinity at high fluences (> 10¹¹ ions/cm²). The scanning electron micrographs (SEM) exhibit increased porosity of the polymer electrolyte films after low fluence ion irradiation.     

Super-protonic phase transition and fast ionic conductivity of Li+ in [Li0.2(NH4)0.8]2TeCl6

The differential scanning calorimetry diagram of [Li_0.2(NH₄)_0.8]₂TeCl₆ showed one anomaly at 526 K accompanied with a shoulder at 505 K.The conductivity plot exhibits two anomalies at 496 and 526 K, which characterize the beginning and the end of the crossing to superionic conductor state. The low temperature conduction is ensured essentially by Li⁺. A sudden jump confirms the presence of a superionic protonic transition related to the fast motion of Li⁺ and H⁺ ions. Above 526 K, the high temperature phase is characterized by high electrical conductivity (10^− 3 Ω^− 1 m^− 1) and low activation energy (E_a < 0.3 eV).The dielectric constant evolution as a function of frequency and temperature revealed the same anomaly.Transport properties in this material appear to be due to Li⁺ and H⁺ ions' hopping mechanism.     

7Li and 51V NMR study on Li+ ionic diffusion in lithium intercalated LixV2O5

Li_xV₂O₅ (0.4 < x < 1.4) prepared by solid-state reaction were studied by ⁷Li and ⁵¹V NMR spectroscopy. ⁷Li NMR spectra showed a narrowing of the line width in relation to Li⁺ionic diffusion. Analysis of Li_xV₂O₅ using a Debye-type relaxation model showed a low activation energy ∼0.07 eV in the sample of x = 0.4 below room temperature, and revealed a Li⁺ionic diffusion with larger activation energy ∼0.5 eV above 450 K in lithium-rich samples. The latter is ascribed to the existence of a multi-phase system comprising stable ɛ- and γ-phases, resulting from complicated phase transitions at high temperature. These shapes and shifts enable the classification of the β-, ɛ-, δ-, and γ-phases. The ionic diffusion of Li⁺ ions is discussed in relation to the complicated phase transitions.     

DFT study of carbon monoxide adsorption on α-Al2O3(0001)

The adsorption of CO on α-Al₂O₃(0001) was studied using the DFT-GGA computational method and on α-Al₂O₃ powder experimentally by Infra red spectroscopy. The core and valence level regions of α-Al₂O₃(0001) single crystal surface were also studied experimentally. Ar ions sputtering of the surface results in a slight but reproducible decrease in the XPS O2p lines in the valence band regions due to preferential removal of surface (and near surface) O atoms. Core level XPS O1s and Al2p further confirmed oxygen depletion with an associated surface stoichiometry close to Al₂O_2.9. The adsorption energy of CO was computed and found equal to 0.52 eV for θ = 0.25, it decreased to 0.42 eV at θ = 1. The IR frequency of νCO was also computed and in all cases it was blue shifted with respect to gas phase CO. The shift, Δν, decreased with increasing coverage where it was found equal to 56 cm^? 1 for θ = 0.25 and decreased to 30 cm^? 1 for θ = 1. Structural analyses indicated that the change in the adsorption energy and the associated frequency shift is due to surface relaxation upon adsorption. Experimentally the adsorption of CO gave rise to one main IR peak at 2154 cm^? 1 at 0.3 Torr and above. Two far smaller peaks are also seen at lower pressures of 0.03–0.2 Torr at 2189 and 2178 cm^? 1. The isosteric heat of adsorption was computed for the IR band at 2154 cm^? 1 and was found equal to 0.2 eV which did not change with coverage in the investigated range up to θ = 0.6.     

First-principles study on electronic states of SrWO4 crystals containing F-type color centers

The electronic structures of the SrWO₄ crystals containing F-type color centers are studied within the framework of the fully relativistic self-consistent Dirac–Slater theory using a numerically discrete variational (DV-X^α) method. The calculations indicate that either F or F⁺ center has donor energy level within the forbidden band. The electronic transition energies from the two donor levels to the bottom of the conduction band are 1.82 eV and 2.28 eV corresponding to the 685 nm and 545 nm absorption bands, respectively. It is, therefore, concluded that the 545–685 nm absorption bands are originated from the F and F⁺ center in SrWO₄ crystal respectively.     

A time-resolved luminescence spectroscopy study of non-linear optical crystals K2Al2B2O7

We report the results of complex study of luminescence and dynamics of electronic excitations in K₂Al₂B₂O₇ (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2 eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21 eV) measured at 7 K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5 eV were detected and assigned to charge-transfer absorption from O^2? to Fe³⁺ ions; the intrinsic PL band at 3.28 eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54 eV were separated; the strong PL band at 1.72 eV was revealed and attributed to a radiative transition in Fe³⁺ ion.     

Energy relaxation through the π*-state in C,F and O K-shell excited CF3COCH3

Total photoabsorption spectra of CF₃COCH₃ were measured in the C, F and O K-shell regions and the peak assignments were tentatively given. The K-shell electrons of C, F and O atoms were selectively excited into the π^* orbital. The kinetic energy (KE) distribution of CF₃⁺ formed through the π^* states gave the maxima at KE = 0 and 0.43 eV. The yield of CF₃⁺ with KE = 0 eV increased from 10 to 50% by changing the excitation sites from F 1s to O 1s. This finding was reasonably understood by considering that intramolecular energy flows from the initially excited K-shell electron to vibrational modes of CF₃ group. The KE distribution of CH₃⁺ showed a mirror image of that for CF₃⁺.