Electronic energy band calculation in β-PbO2 comparison with SnO2 and GeO2 energy band structures

The energy band structure of β-PbO₂ is determined semi-empirically by the Kohn-Korringa-Rostoker method. It is believed to be the first PbO₂ calculated band structure that appears in literature. The direct band gap value that is obtained directly from this method is 2.7eV. It is lowered to the value of 1.6 eV which seems to be the most likely value of β-PbO₂ energy gaps that were already obtained. This energy band structure is compared with those of other oxides whose lattices belong to the same space group (D¹⁴_4h).     

Interference of resonance luminescence of exciton polaritons in CuGaS2 crystals

The nonmodulated and wavelength-modulated reflection spectra of CuGaS₂ crystals for the polarization EIIc of 10 K are studied. The states n = 1, 2 and 3 of the excitons Γ₄ (A-excitons) and n = 1, n = 2 of B- and C-excitons are found. The nonmodulated absorption spectra for the polarization E⊥c at 10 K have been studied. The states n = 1, 2 and 3 of Γ₅ excitons are found. The main parameters of the A (Γ₄, Γ₅) and B, C exciton series at the energies of the longitudinal and transverse excitons Γ₄ for the states n = 1 and n = 2, the effective masses of electrons and holes are determined. The photoluminescence peaks were observed at n = 3 and n = 4 of the excitons Γ₅ in the luminescence spectra excited by the line 4880 Å of Ar⁺ laser. In the luminescence spectra the interference is found.     

Electronic energy band calculations in SnO2

The energy band structure of SnO₂ is determined semi-empirically by the Kohn-Korringa-Rostoker method. A Hartree-Fock-Slater potential model is used for Sn⁴⁺. For O²⁻, we use a HFS potential model corrected by the introduction of an additional Slater orbital. The band gap value which is obtained directly from this method is 4.5 eV; it is lowered to the value of 3.8 eV by fitting the mean potential value.     

Bound exciton in CuGaS2

In CuGaS₂ crystals absorption and luminescence spectra at the temperature 9 K at excitation by different wavelengths of Ar laser are investigated. A series of lines available in luminescence and absorption spectra is found. Another series of lines is found only in absorption spectra. The found series of lines of absorption and luminescence are determined by excitons bound on neutral acceptor. A model of electron transitions between the energy levels of the exciton bound on neutral acceptor is proposed.     

Temperature dependence of the Urbach energy in ordered defect compounds Cu-III3-VI5 and Cu-III5-VI8

Two previous models used with success in Cu-III-VI₂ semiconductors have been employed to study the temperature dependence of the Urbach energy in ordered compounds Cu-III₃-VI₅ and Cu-III₅-VI₈. The model which contains two variable parameters seems to explain better the data over the whole temperature range studied. However, the ordered vacancy or the donor acceptor defect pair in the cation sublattice provides new features in these compounds that need further study.     

Optical spectra and energy band structure of AgAsS2 crystals

Ground and excited states of three exciton series are observed in the region of fundamental absorption edge of AgAsS₂ crystals. The contours of exciton reflection spectra are calculated and the main parameters of excitons and energy bands are determined in the center of Brillouin zone. The optical reflection spectra are investigated at 30 K in E∥c and E⊥c polarizations in AgAsS₂ crystals in the region of 2-6 eV. The optical functions are calculated from the reflection spectra and a scheme of electronic transitions responsible for peculiarities of reflection spectra deep into the absorption band is proposed.     

On the Urbach rule in sulphur-implanted Cu6PS5I superionic conductors

Cu₆PS₅I superionic crystals, grown using chemical vapour transport, were implanted by sulphur ions. The ion implantation effect on the phase transitions is studied by temperature isoabsorption investigation of the optical absorption edge. For the implanted crystals the optical absorption edge shape is studied in the temperature range 77-320 K, the parameters of exciton-phonon interaction, resulting in the Urbach behaviour of the optical absorption edge, are determined, the temperature dependences of the optical pseudogap and Urbach energy are obtained. The implantation effect on the ordering-disordering processes in Cu₆PS₅I superionic conductors is studied.     

Low energy sputtering of neutral Cu2 molecules

The ratios of relative yields of neutral sputtered Cu₂ molecules to neutral sputtered Cu atoms were found to be linearly proportional to the sputtering yield of Cu, from a Cu target under bombardment by Ar⁺ ions (energy 50–90 eV), as determined by secondary neutral mass spectrometry.     

Low and room temperature measurements and calculations of O2-broadening coefficients in the ν3 band of CS2

O₂-broadening coefficients have been measured for 16 lines in the P and R branches of the fundamental ν₃ band of ¹²C³²S₂ at room and low temperatures (298.0, 273.2, 248.2, 223.2, and 198.2 K), using a tunable diode laser spectrometer and a low temperature cell. These lines from P(62) and R(64) are located in the spectral range 1519-1547 cm⁻¹. The collisional half-widths are obtained by fitting each observed profile with the Voigt and Rautian lineshape models. The broadening coefficients have also been calculated at all experimental temperatures using a semiclassical calculation performed by considering in addition to the electrostatic quadrupole-quadrupole interaction, a simple anisotropic contribution. Finally, from all the results, the parameter n of the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

Photoluminescence decay affected by variable range hopping in band tail in amorphous As2S3

Photoluminescence decay was observed with various excitation energies and at various temperatures in amorphous As₂S₃. The decay at high temperature or with the high excitation energy had the $\text{t}{}^{\mathrm{<mtext>-3</mtext><mtext>2</mtext>}}$ long time behavior. This decay is concluded to arise from the combination of the tunneling recombination and the variable range hopping of carriers in the band tail.     

Structure of the free exciton luminescence band of heteroepitaxial ZnSe/GaAs layers

The exciton reflectance and photoluminescence spectra of epitaxial ZnSe/GaAs layers with a thickness of 2–4 μm are investigated in the temperature range 10–120 K. It is shown that one of the causes of the formation of the doublet structure of the A _n=1 photoluminescence band is interference of the exciton radiation at the boundaries of the near-surface dead layer. Fiz. Tverd. Tela (St. Petersburg) 40, 881–883 (May 1998)     

Bonding energetics in HF and their relation to H2 and F2

The changes in total and kinetic energies of the HF molecule have been studied as a function of internuclear separation R. In addition the variation of the electron-electron potential energy with R has been displayed. The relation to energy changes in H₂ and F₂ is discussed.     

Low energy Ar-ion bombardment effects on the CeO2 surface

The structure and electronic properties of epitaxial grown CeO₂(1 1 1) thin films before and after Ar⁺ bombardment have been comprehensively studied with synchrotron radiation photoemission spectroscopy (SRPES). Ar⁺ bombardment of the surface causes a new emission appearing at 1.6 eV above the Fermi edge which is related to the localized Ce 4f¹ orbital in the reduced oxidation state Ce³⁺. Under the condition of the energy of Ar ions being 1 keV and a constant current density of 0.5 μA/cm², the intensity of the reduced state Ce³⁺ increases with increasing time of sputtering and reaches a constant value after 15 min sputtering, which corresponds to the surface being exposed to 2.8 × 10¹⁵ ions/cm². The reduction of CeO₂ is attributed to a preferential sputtering of oxygen from the surface. As a result, Ar⁺ bombardment leads to a gradual buildup of an, approximately 0.69 nm thick, sputtering altered layer. Our studies have demonstrated that Ar⁺ bombardment is an effective method for reducing CeO₂ to CeO_2−x and the degree of the reduction is related to the energy and amount of Ar ions been exposed to the CeO₂ surface.     

Indirect exciton luminescense and Raman scattering in CdI2

Intrinsic luminescence and Raman scattering in 4HCdI₂ have been investigated at 2 K. Weak emission bands observed near the absorption edge are attributed to the phonon-assistes indirect exciton luminescence. Several new Raman lines are observed under resonant excitation in addition to known lines. The symmetry of the phonon modes associated with the indirect transitions as well as with Raman scattering is discussed.     

Time-resolved luminescence of UO2MoO4

Time-resolved spectroscopy and decay-time measurements for the intrinsic and trap emission lines of UO₂MoO₄ supply experimental evidence for fast energy migration among intrinsic centres and from intrinsic to trap centres. The temperature behaviour of the decay time for the main trap lines reveals an energy transfer rate from trap to intrinsic centres in the order of 5×10⁹s^-1, while the transfer rate among intrinsic centres, as estimated from the correlation field splitting, is 3×10¹¹ s^-1.     

Time behaviour of diffuse band emission in Na2 and K2

The C states of sodium and potassium dimers were excited with short laser pulses (about 500 ps) and time evolution of the diffuse bands in Na₂ (413–456 nm) and K₂ (550–583 nm) was observed in fluorescence. The measured decay times were interpreted as lifetimes of unidentified triplet states giving origin to the diffuse bands. Our results contradict the values reported before.     

Magneto-optical study of the I2 bound exciton in ZnTe

The 1L0-phonon replica of the I₂ bound exciton in ZnTe at 2.374 eV is fully resolved into a quintet at fields of 130 kG. Analysis of the data shows that the I₂ complex consists of an exciton bound to an $\text{ionized}$ donor or acceptor; the electron and hole gyromagnetic ratios deduced, $\text{g}{}_{\mathrm{h}}\text{= ? 1.2}$ and g_e = ± 1.7, are in excellent agreement with the values determined from recent spin-flip scattering experiments, viz. g_h = 1.07 ± 0.1, g_e = 1.74 ± 0.05.     

Synthesis and luminescence of SrZnO2 phosphors

SrZnO₂ phosphors have been synthesized by two new methods viz. carbonate decomposition at 1000 °C and combustion synthesis. Phosphors activated with Pb²⁺, Sm³⁺, Tb³⁺, Bi³⁺ and Pr³⁺ could be prepared in one step using the combustion synthesis. Characteristic emission and excitation were observed for Bi³⁺. For the remaining activators excitation spectra always contained a band at 283 nm. Presence of this band for all these different types of activators was interpreted as host sensitization.     

Recombination luminescence mechanisms in Ba3(PO4)2

The effect of hole self-trapping in Ba₃(PO₄)₂ at low temperatures has been studied. The TSL peak at 135 K is due to hole delocalization and diffusion by thermally activated hopping between perfect lattice sites, resulting in a composite uv band, corresponding to the tunneling recombination of holes with localized electrons.     

Low energy electron spectroscopy of N2 in the 11.8–13.8 eV energy range

In the 11.8–13.8 eV energy range differential threshold and energy loss spectra of electrons scattered by N₂ molecules have been obtained at an incident energy of 14.3 eV and with a 30 meV experimental resolution. The study of the angular behaviour of the observed peaks permits us to distinguish between singlet-singlet and singlet-triplet transitions. The predicted F³Π_u and G³Π_u Rydberg states are observed. Also some levels of unknown triplet states are seen at 13.155, 13.395 and 13.635 eV.