A photoelectron spectroscopic study of the second ionisation of the CF(X2Π) radical

The CF(X²Π) radical has been re-investigated with vacuum ultraviolet photoelectron spectroscopy. Two bands were observed and assigned to the ionisations CF⁺(X¹Σ⁺)←CF(X²Π) and CF⁺(a³Π)← CF(X²Π). The first band, which has been observed previously, has an adiabatic ionisation energy of (9.11±0.02) eV and a vertical ionisation energy of (9.55±0.02) eV. For the second band, three vibrational components were observed with the first, the most intense, at an ionisation energy of (13.94±0.02) eV. Analysis of the vibrational structure in the two observed bands allowed ω_e and r_e to be determined as 1810±30 cm⁻¹ and 1.154±0.005 Å, respectively for the first ionic state, CF⁺(X¹Σ⁺), and 1614±30 cm⁻¹ and 1.213±0.005 Å, respectively for the second ionic state, CF⁺(a³Π). Comparison of the ionisation energies and spectroscopic constants obtained has been made with values obtained from recent multi-reference configuration interaction calculations.     

Spectroscopic properties of SbH

Relativistic configuration interaction calculations which include spin-orbit interaction are carried out for nine low-lying ω-ω states and four λ-s states. Spectroscopic properties of six bound ω-ω states are reported. These calculations not only enable assignment of the experimentally observed X₁, X₂, A₁, A₂, and B states but also predict the properties of other electronic states (0⁺(II), 0⁺(IV), 2, 2(II), 1(II), 0⁻) which are yet to be observed. The dissociation energy of SbH is predicted to be 2.7 ± 0.2 eV.     

A1Σu+-X1Σg+ and B1Πu-X1Σg+ fluorescence of 6Li2 and 6Li7Li excited by a krypton ion laser

The A¹Σ_u⁺-X¹Σ_g⁺ and B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li₂ and ⁶Li⁷Li molecules has been studied for all krypton ion laser lines (468.0–799.3 nm) which might be expected to excite such fluorescence. Only two A-X fluorescence series of ⁶Li₂ were found (one excited by 647.1 nm, and one by 752.5 nm). No A-X fluorescence series of ⁶Li⁷Li was found. Five B-X fluorescence series of ⁶Li₂ were found (one each excited by 468.0, 476.2, and 530.9 nm, and two by 568.2 nm). Four B-X fluorescence series of ⁶Li⁷Li were found (one each excited by 468.0 and 482.5 nm and two by 520.8 nm). Calculated Einstein A coefficients and lifetimes for these transitions are also given.     

Coulomb effects in spatially separated electron and hole layers in coupled quantum wells

We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/Al_xGa_1?x As coupled quantum wells (CQWs) at low temperatures (T = 1.4 K) for a broad range of electron-hole (e-h) densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the e-h density both for a zero magnetic field and at high fields for all Landau level transitions; this is in contrast to the electron-hole systems in single QWs where the main features are explained by the band-gap renormalization resulting in a reduction of the PL energy. The observed enhancement of the ground state energy of the system of the spatially separated electron and hole layers with increasing the e-h density indicates that the real space condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has been observed: its relative intensity increased both in PL and in absorption (measured by indirect PL excitation) with increasing density; its energy separation from the direct exciton line fits well to the X ^? and X ⁺ binding energies previously measured in single QWs. The line is therefore attributed to direct multiparticle complexes.     

Rotational analysis of the a3Π-X1Σ+ bands of GaD

A new method of producing strong and clean emission spectra of the gallium hydride/deuteride molecule has been developed. Five bands belonging to the gallium deuteride molecule (GaD) have been photographed under high resolution. The rotational analyses of the bands lying at 5669.14 Å (0-0) and 5675.10 Å (1-1) in the a³Π₁-X¹Σ⁺ transition, 5761.0 Å (0-0) and 5766.20 Å (1-1) in the a³Π_0⁺-X¹Σ⁺ transition, and 5760.85 Å (0-0) in the a³Π_0⁻-X¹Σ⁺ transition have been performed. Accurate rotational constants (B, D) have been determined for the X¹Σ⁺, a³Π_0^± and a³Π_1^± states. The Λ doubling in the a³Π₀ (v = 0) and a³Π₁ (v = 0 and 1) states are obtained.     

Laser Spectroscopy of Cerium Monofluoride: Ligand Field Assignments of Some 4f5d6p← 4f5d6sTransitions

The techniques of selectively detected fluorescence excitation, dispersed fluorescence, and magnetic rotation spectroscopy have been applied to the CeF molecule and used to characterize one [17.6]4.5 electronic state in the ∼2 eV region and three electronic states withT₀< 2000 cm⁻¹:X(1)3.5 and (2)3.5 with Ω = 3.5 and (1)4.5 with Ω = 4.5. Two of these states, the [17.6]4.5 andX(1)3.5 states, had been observed previously [R. M. Clements and R. F. Barrow,J. Mol. Spectrosc.107,119 (1984); Y. Azuma, W. J. Childs, and K. L. Menningen,J. Mol. Spectrosc.145,413 (1991)]. Based on the pattern of Ω-values and the value of ΔG_1/2≈ 550 cm⁻¹, the three low-lying states are assigned to the Ce⁺(4f5d(³H)6s)F⁻superconfiguration. The upper state is assigned to the Ce⁺(4f5d(³H)6p)F⁻superconfiguration on the basis of computed ligand field monopoleB⁰₀(nl,nl) orbital destabilization energies and one-electron transition propensity rules.     

Positron annihilation from excited states of [X-e+] systems

The relative probabilities for the radiative de-excitation 2p₊ → ls₊ versus 2γ-annihilation for the hdot; ns²np⁶2p₊, ²P state of the [X^-e⁺] system with X = F, Cl, Br, and I are presented. It is shown that a positron captured into a 2p₊ orbital undergoes annihilation with electrons of the system instead of radiative transition to the ground state of the [X^-e⁺] system.     

Influence of Cu doping on the microstructure,optical properties and photoluminescence features of Cd0.9Zn0.1S nanoparticles

Cd_0.9−xZn_0.1Cu_xS (0≤x≤0.06) nanoparticles were successfully synthesized by a conventional chemical co-precipitation method at room temperature. Crystalline phases and optical absorption of the nanoparticles have been studied by X-ray diffraction (XRD) and UV–visible spectrophotometer. XRD confirms the phase singularity of the synthesized material, which also confirmed the formation of Cd–Zn–Cu–S alloy nanocrystals rather than separate nucleation or phase formation. Elemental composition was examined by the energy dispersive X-ray analysis and the microstructure was examined by scanning electron microscope. The blue shift of absorption edge below Cu=2% is responsible for dominance of Cu⁺ while at higher Cu concentration dominated Cu²⁺, d–d transition may exist. It is suggested that the addition of third metal ion (Cu²⁺/Cu⁺) is an effective way to improve the optical property and stability of the Cd_0.9Zn_0.1S solid solutions. When Cu is introduced, stretching of Cd–Zn–Cu–S bond is shifted lower wave number side from 678 cm⁻¹ (Cu=0%) to 671 cm⁻¹ (Cu=6%) due to the presence of Cu in Cd–Zn–S lattice and also the size effect. The variation in blue band emission peak from 456 nm (∼2.72 eV) to 482 nm (∼2.58 eV) by Cu-doping is corresponding to the inter-band radiation combination of photo-generated electrons and holes. Intensity of red band emission centered at 656 nm significantly increased up to Cu=4%; beyond 4% it is decreased due to the quenching of Cu concentration.     

Shift of a Γ-X junction due to hydrostatic pressure

Hydrostatic pressure causes a shift of a Γ-X junction in the direction opposite to the band-gap gradient. The shift is of the order of 1μ/kbar in the samples investigated. From the shift and the band-gap gradient, the intervalley pressure coefficient (?/?P) (E_X–E_Γ) is estimated to be — 9·0^-6 eV/bar for the composition of Al_xGa_1-xAs corresponding to the Γ-X crossover.     

The electronic spectrum of bismuth monofluoride: An 0+ ← X10+ band system at 3838 Å

Emission bands of BiF (in the region of 3800 Å), formerly designated as belonging to the B-X₁0⁺ and A₃-X₁0⁺ transitions, have been photographed and rotationally analyzed under high resolution. These bands have been found to belong to an 0⁺ ← X0⁺ system. Extensive rotational and vibrational perturbations have been observed and the nature of the perturbing state is discussed.     

VUV excitation of luminescence in pure and Tl+ doped KI

Excitation spectra of pure and Tl⁺ doped KI have been measured at room temperature (RT) and liquid nitrogen temperature (LNT) between 13 and 30 eV. Energy transfer between the host lattice ions and the Tl⁺ impurities, and intrinsic recombinaton of electron-hole pairs, have been studied at different temperatures and excitation energies. Energy transfer has been observed only at RT while at LNT the intrinsic recombination, V_k centers-electrons, is the dominant process.     

Observation of charged X−and X+excitons and metal-to-insulator transition in CdTe/CdMgZnTe modulation-doped quantum wells

The positively and negatively charged excitons,X⁺andX⁻, respectively, are identified by their magnetic circular dichroism in the absorption spectra of modulation-doped CdTe/Cd_0.69Mg_0.23Zn_0.08Te multiple quantum wells at small carrier densities (≈10¹⁰cm⁻²). In these quantum wells with a width of 8 nm the binding energies of the second electron of theX⁻exciton and of the second hole of theX⁺exciton are very similar, 2.9 meV and 2.6 meV, respectively. At larger hole densities a transition to the conducting state is observed. In a sample with intermediate hole density (low 10¹¹cm⁻²) the insulating phase is restored by application of a magnetic field.     

Luminescence above the gap in heavily Zn-doped GaAs

Several distinct features have been observed in the photoluminescence spectrum of heavily Zn-doped GaAs, in the range between 1.65eV to 2.25eV. They are attributed to direct recombination across the E_o+?_o gap and to indirect processes related to X^c₁ and X^c₃. The X^c₁ minima are thus located to be 1.935±0.01eV above the top of the valence band at 100K. Their shear deformation potential $\text{E}$^X₂ is found to be $\text{E}{}^{\mathrm{X}}{}_2\text{=5.5±2eV}$.     

Fine structure in optical transitions from 3d and 4d core levels to the lower conduction band in Ga-V and In-V compounds

We investigate fine structure in energy derivative reflectance (EDR) spectra near 20–21 eV in GaP, GaAs, and GaSb, and near 18–20 eV in InP, InAs, and InSb. Derived energy values for X^c₁ thresholds in GaP and GaSb, and L^c₁ and X^c₁ thresholds in GaAs, agree well with previous Schottky barrier electroreflectance (ER) results. L-X structure splittings in EDR spectra of InAs and InSb, for which Schottky barrier ER measurements cannot be performed, are 0.29 and 0.44 eV, respectively. Estimates of expected locations of these structures, based on XPS and absorption data and band structure calculations, indicate energy deficits of 0.2 eV for In4d-L^c₁ and 0.5 eV for In4d-X^c₁ transitions, respectively.     

Photoemission via bloch states and evanescent band gap states for Cu(110)

Normal emission photoelectron spectra from Cu(110) using polarized synchrotron radiation (hv < 35 eV) can be explained with a direct transition model using realistic final state bands. Prominent surface photoemission via evanescent final states is observed in the large X′₅-X₁ conduction band gap. Accurate valence band eigenvalues at K and X have been determined.     

Oscillator strengths for SiH and SiH deduced from the solar spectrum

Recent identifications of SiH (A²Δ-X²Π) and SiH⁺ (A¹Π-X¹Σ⁺) in the solar photospheric spectrum have enabled us to derive absolute oscillator strengths for the (0, 0) bands of these transitions: f₀₀(SiH) = 0.0033 and f₀₀(SiH⁺) = 0.0005. Our result for SiH is compared with other values.     

The spectra and structure of indium iodide: The rotational and vibrational constants of the B 1 state

The rotational constants of the B 1 state of indium iodide are reported for the first time as B_e = 0.037533 cm⁻¹ and α_e = 0.000289 cm⁻¹ while T_e = 25050.60 cm⁻¹ for the B1-X0⁺ transition. Accurate vibrational constants are also computed from measured Q heads as ω_e= 146.36 cm⁻¹ and ω_eχ_e = 2.20 cm⁻¹.     

Laser spectroscopy of the B[21.68]8-X8, B′[21.65]8-X8 and C[22.3]7-X27 transitions of holmium monofluoride

The spectrum of holmium monofluoride (HoF) in the blue (420-480 nm) region has been studied using laser-induced fluorescence. Previous work [J. Phys. B 7 (1974) L234] had assigned several bands in this region to the B8-X8 transition. By obtaining wavelength selected laser excitation spectra at high resolution and rotationally analyzing seven bands in this region, we have shown that not all the bands previously assigned to the B8-X8 system belong to the same electronic transition and have identified three separate transitions which we have labelled B8-X8, B′8-X8, and C7-X₂7. Preliminary low resolution dispersed fluorescence spectra have shown several excited states at energies greater than 4000 cm⁻¹ above the ground state and, though not all could be assigned, ligand field theory calculations are consistent with assigning them to the first excited spin-orbit component of the Ho⁺(4f¹⁰6s²)F⁻ ground state configuration or to the first excited configuration, Ho⁺(4f¹¹6s)F⁻. The results of the dispersed fluorescence experiments also tentatively place the X₂7 state at ∼70 cm⁻¹ above the ground X7 state.     

Thermoluminescence in room temperature λ-irradiated KCl: Na crystals

Thermoluminescence in KCl:Na (>250 ppm) crystals has been examined. Analysis indicates that processes involved follow the first-order kinetics. The frequency factor (∼10¹⁰s⁻¹) obtained favours an electron-hole recombination occuring after an electron has passed through the conduction band. It is also suggested that the 440 nm band peak found in pure samples in resolved into 500 nm and 430 nm band peaks in Na-doped samples.     

Cathodoluminescence of copper and nickel surfaces

Cathodoluminescence spectra of clean and oxidized Cu(100) and Ni(100) surfaces, using 60–1000 eV electron bombardment, has been measured. A broad peak at 310 nm has been observed for both clean Cu and Ni surfaces. This peak is attributed to radiative recombination of electrons from the point X'₄ with holes at the point X₅ of the energy band diagram. A narrow peak at 520 nm has been found to correlate with the growth of oxide on the Cu and Ni surfaces. This peak can be attributed to electronic transitions involving energy levels of the O^2- ions. The cathodoluminescence technique appears useful for studying the initial growth of metal oxides.