The origin of K2, Rb2 and Cs2 triplet 13Πg−X3Σ+u bands in discharge

The absorption and emission spectra of potassium, rubidium and caesium low-pressure discharges have been studied at the far blue wings of resonance D2-lines. The observed diffuse bands were attributed to the 1³Π_g?X³Σ⁺_u transition. Experiments revealed the recombination ²P + ²S nature of these bands, and the corresponding rate coefficients were obtained. Energies of the higher excited states as well as the X³Σ⁺_u -state well depths for K₂, Rb₂ and Cs₂ molecules were estimated.     

Cathodoluminescence of thorium in the presence of O2, CO and gas mixtures of CO-O2 and CO-H2

The cathodoluminescence (2–6 keV incident electrons) observed from thorium (111) and (533) crystal faces was recorded and analyzed for surfaces produced under various conditions. The blue luminescence observed in the presence of a partial oxygen pressure ～ 133 μPa (～10^-6 Torr) was found to consist of a broad asymmetric major band that peaked around 468 nm on which weak bands or lines were superimposed at approximately 433, 489, 502, and 534 nm. The emission was almost totally extinguished in the presence of a partial CO pressure ～ 133 μPa (～10^-6 Torr). The thorium-oxygen cathodoluminescence (CL) is interpreted as arising from the formation of ThO₂ and the excitation of luminescence centers by the incident electron beam and their subsequent decay. The major luminescence at 468 nm arises from F centers in ThO₂. The weak bands at 433 and 534 nm may arise from surface F⁺ and F centers designated as F⁺_s and F_s. The former may also be due to an OH luminescence center. The two longer wavelength lines (489, 502 nm) superimposed on the broad major band at approximately 468 nm are interpreted as arising from Pr³⁺ impurities in the thorium lattice that gave rise to fluorescence emission. The line at 468 nm also may be due in part to the fluorescence of ThO. The cathodoluminescence spectra observed in the presence of CO, and (CO+O₂) and (CO+H₂) gas mixtures were consistent with an interpretation that O₂ in the gas phase was required in order to obtain ThO₂ on and below the surface to produce significant luminescence. Auger spectroscopy showed that exposure to CO left approximately as much oxygen on the surface as in the case of O₂ but did not produce appreciable cathodoluminescence.     

The ν2, 2ν2, 3ν2, ν4, and ν2 + ν4 bands of 15NH3

The ir absorption of gaseous ¹⁵NH₃ between 510 and 3040 cm^?1 was recorded with a resolution of 0.06 cm^?1. The ν₂, 2ν₂, 3ν₂, ν₄, and ν₂ + ν₄ bands were measured and analyzed on the basis of the vibration-rotation Hamiltonian developed by V. ?pirko, J. M. R. Stone, and D. Papou?ek (J. Mol. Spectrosc.60, 159–178 (1976)). A set of effective molecular parameters for the ν₂ = 1, 2, 3 states was derived, which reproduced the transition frequencies within the accuracy of the experimental measurements. For ν₄ and ν₂ + ν₄ bands the standard deviation of the calculated spectrum is about four times larger than the measurements accuracy: a similar result was found for ν₄ in ¹⁴NH₃ by ?. Urban et al. (J. Mol. Spectrosc.79, 455–495 (1980)). This result suggests that the present treatment takes into account only the most significant part of the rovibration interaction in the doubly degenerate vibrational states of ammonia.     

The 2ν2 and ν1 bands of HD16O

The 2ν₂ and ν₁ bands of HDO lying in the region 2235–3115 cm^?1 were analyzed using Fourier transform spectra of “pure” D₂O and of H₂OD₂O mixtures. From this analysis, an extended and precise set of rotational levels belonging to the (000), (020), and (100) vibrational states was derived. Using the (000) levels together with the existing microwave data as input in a least-squares fit, it was possible to obtain reliable rotational constants for the ground state of the HDO molecule.     

High resolution infrared spectrum of the ν2 + ν3 and ν1 + ν2 bands of ozone

The vibration-rotation bands ν₁ + ν₂ and ν₂ + ν₃ of ozone appearing in the 5.7 μm region have been recorded at a resolution of 0.019 cm^?1 with a SISAM spectrometer. The rotational levels of the (110) and (011) vibrational states have been fitted using a Hamiltonian which takes into account the Coriolis interaction between these two states. The rotational and coupling constants deduced from this study have been used to calculate a list of the vibration-rotation lines which is of interest for high resolution studies of atmospheric spectra in the 1670–1890 cm^?1 region.     

Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2 and (CH3)2S2

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂, and (CH₃)₂S₂ have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.     

Study of isotopic 13C2 bands of the Deslandres-D'Azambuja system

The emission bands of the Deslandres-D'Azambuja system of ¹³C₂ have been obtained in the region 320–450 nm using a source containing enriched ¹³C. Measured line positions of the 2-0, 2-1, 1-0, 0-0, 1-1, 1-0, 2-1, and 3-2 bands were fitted by a least-squares procedure to determine the rotational constants and the origin for each band. The fitted origins were used as input in calculation of the vibrational constants for both C¹Π_u electronic states involved in the transition.     

Ni2+ emission in SrF2

Luminescence measurements of X-irradiated SrF₂:Ni are reported. After X-irradiation two emission bands have been found. One of them peaked at 293 nm and has an excitation band at 267 nm. The other one at about 770 nm, which is much weaker, has an excitation band at 274 nm. Both emission bands are also observed under X-ray excitation. A comparison with some previous studies of the absorption and thermoluminescence properties of X-irradiated SrF₂:Ni indicates that the emission bands are due to two different kinds of Ni²⁺ centers. The proposed emission mechanisms are similar to those found in CaF₂:Ni.     

Photoluminescence of F2+2 centres in additively coloured magnesium oxide

The principle luminescence bands excited in additively coloured MgO by radiation in the wavelength range 170–400 nm are observed at wavelengths of 520, 475, 441 and 375 nm. Polarised luminescence and uniaxial stress measurements on the 441 nm band, the radiative lifetime of 25 msec at 1.6 K and temperature dependence of luminescence intensities of the 375, 441 and 375 nm bands are consistent with the 441 nm band being due to ³B_1u → ¹A_g transitions of the F²⁺₂ centre.     

The vibration-rotation spectrum of methinophosphide: l-Type doubling, l-type resonance and the ν2, 2ν2, and 3ν2 bands of H12CP; The ν1 and ν2 bands of H13CP

The vibration-rotation bands ν₂, 2ν₂, and several “hot” bands of H¹²CP have been recorded and assigned. The states with v₂ = 2, perturbed by l-type resonance and l-type doubling effects have been analyzed on the basis of the existing theory. The energy difference between the 02²0 and the 02⁰0 states was found to be 17.5095 (19) cm^?1. Because of insufficient data, the states with v₂ = 3 could not be corrected for l-type resonance interaction and therefore only an effective l-type doubling constant was obtained. The ν₁ and ν₂ bands of the H¹³CP isotopic molecule (present at natural concentration) were also identified and their spectroscopic constants obtained. The value of I_e for H¹²CP is found to be 25.18793 (26) amu Ų.     

Opto-galvanic spectroscopy of some molecules in discharges: NH2, NO2, H2 and N2

The change of the discharge voltage when laser light crossing the discharge is tuned to a molecular transition has been measured. Experiments have been performed in the wavelength region between 570 nm and 620 nm with discharges in NH₃, NO₂, H₂, N₂, O₂ and argon. Transitions from the ground states of NH₂ and NO₂ and transitions from metastable states of N₂ and H₂ have been detected. The spacial dependence of the opto galvanic in a low pressure dc-discharge of H₂ and N₂ has been studied.     

Luminescence of Ce and Pr doped Sr2Mg(BO3)2 under VUV-UV and X-ray excitation

This report presents the luminescence properties of Ce³⁺ and Pr³⁺ activated Sr₂Mg(BO₃)₂ under VUV-UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46 729, 44 643, 41 667, 38 314 and 29 762 cm⁻¹ (i.e. 214, 224, 240, 261 and 336 nm) for Ce³⁺ in the host lattice. The doublet Ce³⁺ 5d→4f emission bands were found at about 25 840 and 24 096 cm⁻¹ (387 and 415 nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce³⁺ in Sr₂Mg(BO₃)₂ were investigated. For Pr³⁺ doped samples, the lowest 5d excitation band was observed at about 42017 cm⁻¹ (238 nm), a dominant band at around 35714 cm⁻¹ (280 nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce³⁺ and Pr³⁺ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100 photons/MeV of absorbed X-ray energy for the samples Sr_1.86Ce_0.07Na_0.07Mg(BO₃)₂ and Sr_1.82Pr_0.09Na_0.09Mg(BO₃)₂ at RT, respectively.     

Intrinsic ultraviolet luminescence from Lu2O3, Lu2SiO5 and Lu2SiO5:Ce

Radioluminescence and thermally stimulated luminescence measurements on Lu₂O₃, Lu₂SiO₅ (LSO) and Lu₂SiO₅:Ce³⁺ (LSO:Ce) reveal the presence of intrinsic ultraviolet luminescence bands. Characteristic emission with maximum at 256 nm occurs in each specimen and is attributed to radiative recombination of self-trapped excitons. Thermal quenching of this band obeys the Mott-Seitz relation yielding quenching energies 24, 38 and 13 meV for Lu₂O₃, LSO and LSO:Ce, respectively. A second intrinsic band appears at 315 nm in LSO and LSO:Ce, and at 368 nm in Lu₂O₃. Quenching curves for these bands show an initial increase in peak intensity followed by a decrease. Similarity in spectral peak position and quenching behavior indicate that this band has a common origin in each of the samples and is attributed to radiative recombination of self-trapped holes, in agreement with previous work on similar specimens. Comparison of glow curves and emission spectra show that the lowest temperature glow peaks in each specimen are associated with thermal decay of self-trapped excitons and self-trapped holes. Interplay between the intrinsic defects and extrinsic Ce³⁺ emission in LSO:Ce is strongly indicated.     

Optical study of ZnP2 nanoparticles in zeolite Na-X

Nanoparticles of the II-V semiconductor (ZnP₂) were prepared and investigated. ZnP₂ nanoparticles were incorporated into zeolite Na-X matrix. Absorption, diffuse reflection (DR) and photoluminescence (PL) spectra of ZnP₂ nanoparticles were measured at the temperature of 77 K. Five bands B₁-B₅ are observed in both the DR and PL spectra demonstrating the blue shift from the line of free exciton in bulk crystal. We attribute the B₁-B₅ bands to five stable nanoparticles with size less than the size of zeolite Na-X supercage. We observed Stokes shift of the PL bands with respect to the absorption bands. This dependence of this Stokes shift on the particle size is nonmonotonic.     

Photoluminescence of CdGeP2 and (Cd,Mn)GeP2

Photoluminescence of CdGeP₂ (112) single crystal and CdGeP₂ epitaxial film grown on GaAs (001) substrate have been studied and their spectral similarity found. Spectral bands associated with donor/acceptor transitions peak at close energies for both substances and all are lower than the energy gap of the chalcopyrite crystal.On the other hand, the growth of (Cd,Mn)GeP₂ ferromagnetic layer on CdGeP₂ (112) single crystal was performed to make it possible observation of PL from both the ferromagnetic layer and substrate. The green laser excitation (514, 532 nm) produces a proper photoluminescence similar to that in the undoped CdGeP₂ crystal and film. An extra emission from the ferromagnetic-nonmagnetic heterojunction occurs to extend up to photon energies exceeding E_g of the host semiconductor. The short wavelength photoluminescence is to be due to (Cd,Mn)GeP₂ dilute magnetic semiconductor (DMS). This fact states that Mn-doped II-IV-V₂ chalcopyrites are closer to II-VI DMS than to another group III-V DMS, where the heavy Mn-doping suppresses photoluminescence at all. Features of the observed short wavelength emission are discussing based on the temperature and spectral analyses.     

The ν2 + ν4 and 2ν2 isotropic Raman bands of 12CH4

The purely isotropic Raman spectrum of the ν₁ band, the ν₂ + ν₄ band (enhanced through interaction with ν₁), and the 2ν₂ band of ¹²CH₄ was obtained with a spectral resolution of 0.30–0.35 cm^?1 from exposures with different orientations of the linearly polarized exciting light. The ν₂ + ν₄ and 2ν₂ bands show partially resolved rotational structure. The spectra are interpreted in terms of a model which takes explicitly into account vibrational and rovibrational interactions with other vibrational states, using molecular constants determined primarily from infrared spectra. The computed contours are in excellent agreement with the experimental ones and the observed and calculated peak wavenumbers agree within one tenth of the spectral resolution limit, except for a small region near the ν₁ band. The good overall agreement represents an independent check on the overall correctness of the previously reported molecular constants. A detailed discussion is given of the contributions to the intensities of individual transitions from the three transition moment matrix elements, which in an isolated-band model are the intensity parameters of the ν₁, 2ν₄, and 2ν₂ isotropic bands, respectively.     

On the photoelectron spectrum of CS2

High-resolution photoelectron spectra of CS₂ have been obtained by photoionization with the He(I) (58.4 nm), Ne(I) (73.58–74.37 nm) and Ar(I) (104.8–106.7 nm) resonance lines. The resolution of about 17 meV was further improved by deconvolution of the experimental data. The formation of the X?²Π_g and B?²Σ_u⁺ states is accompanied by a weak ν₂ excitation. The spin—orbit splitting of the òΠ_u state is completely resolved, and a value of 186 cm^?1 is reported. We confirm the value of 12.689 eV for the ionization threshold of the Ã²Π ^u3/2 state, and show that the small peak observed at lower energy is due to a hot band.     

非线性光学晶体HgGa2S4 和 Hg0.5Cd0.5Ga2S4的能带结构、化学键及光学性质研究

用密度泛函理论和非谐振子模型计算了晶体HgGa₂S₄和Hg_0.5Cd_0.5Ga₂S₄的能带结构、态密度、化学成键及线性、非线性光学性质。结果表明：HgGa₂S₄的价带顶部主要是Ga-S成键态的贡献，导带底部主要是Ga-S反键态的贡献; Hg_0.5Cd_0.5Ga₂S₄的价带顶部主要由S-3p轨道组成，导带底部主要是Ga-S反键态的贡献。布居分析表明Ga-S键主要是共价成分，而Hg-S和Cd-S键主要是离子成分。HgGa₂S₄的折射率计算值与实验值在低能量区很好吻合。另外，HgGa₂S₄的能隙计算值比Hg_0.5Cd_0.5Ga₂S₄小，而二阶非线性极化率比Hg_0.5Cd_0.5Ga₂S₄大。     

Luminescence characteristics of Eu2+ activated Ca2SiO4 Sr2SiO4 and Ba2SiO4 phosphorsfor white LEDs

<正>This paper investigates the luminescence characteristics of Eu²⁺ activated Ca₂SiO₄,Sr₂SiO₄ and Ba₂SiO₄ phosphors. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices,and show different emission colour variation caused by substituting M²⁺ cations for smaller cations.This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence.These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes（LEDs） based on ultraviolet chip/phosphor technology.     

Model calculation of the electronic structure and spectroscopy of Hg2

Energy curves and transition moments of the excited valence states of Hg₂ were obtained in a model calculation based on calculated Mg₂ energy levels and the assumption that the asymptotic spin-orbit matrix elements for the Hg atom are applicable to the molecular states. The spin-orbit and orbital-rotational interaction of the excited states of Hg₂ is analyzed in both a Hund's case (c) and (a) representation. The intermediate (a) → (c) transition moments are obtained as a function of the internuclear distance. The effect of the orbital-rotational interaction which introduces Hund's case (b) and (e) couplings is found to be small for transitions among excited states under the conditions normally encountered for populating excimer states.Using the energy level positions and transition moments, the observed spectra and predicted spectra are compared for both radiative transitions including the ground state and among the excited states. The lifetime of the $\text{1}{}_{\mathrm{u}}\text{(}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{)}$ excimer state is calculated to be 1.4 μsec with the 335 nm band assigned to the $\text{1}{}_{\mathrm{u}}\text{→ X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transition. The 485 nm bands cannot be assigned to any Hg₂ transitions. Strong bound-continuum absorptions are predicted for the 485 nm bands. On the other hand, the 335 nm emission is predicted to be absorbed by bound-bound transitions only.