SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.     

N2O+离子A2Σ+电子态高振动能级的转动结构分析

利用一束波长为36055nm的激光,通过(3+1)共振多光子电离方法制备纯净的且处于X²Π_1/2,3/2(000)态的N₂O⁺离子,用另一束激光激发所制备的离子到第一电子激发态A²Σ⁺的不同振动能级,然后解离,通过检测解离碎片NO⁺强度随光解光波长的变化,得到了转动分辨的N₂ 关键词： 2O⁺离子A²Σ⁺电子态')" href="#">N₂O⁺离子A²Σ⁺电子态 共振增强多光子电离 光解碎片激发光谱 光谱常数     

Investigation of phase transitions and thermal expansion of some complex tungsten-containing oxides

The phase transitions have been investigated and the thermal expansion coefficients have been determined in compounds with a structure of brannerite, defect pyrochlore, and tungsten bronze of the general formula M ^I A ^VWO_{6 − δ} (M ^I = □, H₃O, Li, Na, K, Rb, and Cs; A ^V = V, Nb, Sb, and Ta; δ = 0, 0.5) by high-temperature X-ray diffraction and differential thermal analysis. It has been shown that brannerites and tungsten bronze do not undergo phase transitions and the compounds are characterized by a significant anisotropy of the thermal expansion, whereas pyrochlores undergo phase transitions of three types, and thermal deformations in them are determined by the size of M ^I atoms.     

Ab initio calculations on the ground and excited states of InI

Potential energy curves (PECs) of the ground and the low-lying excited states of the InI molecule are computed using the internally contracted multireference singles and doubles configuration interaction with the Davidson correction (ic-MR-CISD + Q) method based on the relativistic effective core potentials (RECPs). The spectroscopic constants are obtained, including the excitation energy (T _e), the equilibrium bond distance (R _e), the dipole moment (μ_e) and the vibrational constants (ω_e and ω_e). Finally, we predict the transition dipole moments, the radiative lifetimes, and the Franc-Condon factors for the transitions of A³Π₀+ ? X¹Σ₀ ⁺ and B³Π^l ? X¹Σ₀ ⁺,. The results reveal that A³Π₀+ and B³Π_l are long-lived states with the lifetimes being of the order of microseconds.     

Structure of low-spin states in the doubly-odd 182Ir nucleus

Low-spin states of ¹⁸²Ir were populated through the β⁺ /EC decay of ¹⁸²Pt . Two strong E2 transitions were observed for the first time: a 25.7keV transition in ¹⁸²Ir and a 34.0keV transition in Re of probable mass A = 178 . Spin and parity, I ^π = 3⁺ , are firmly assigned to the ¹⁸²Ir ground state (g.s.). For the excited states, the parity is established and the spin determined or restricted. These assignments support most of the interpretations of the level structure previously suggested. The systematics for the known 5⁺ → 3⁺ transitions in π h _9/2 ⊗ ν 1/2^-[521] bands is presented. Using a semi-microscopic two-quasiparticle axial-rotor coupling model, particle configurations have been attributed or suggested for most of the coupled states lying at low energy in ¹⁸²Ir .     

The structure of 32S II. Shell model interpretation

The properties of positive-parity states in ³²S are compared to predictions of shell model calculations within the complete s-d basis space using the universal s-d shell Hamiltonian. The experimental T = O spectrum is reproduced to excitation energies between 10 and 11.7 MeV, depending on the level spins. The T = 1 spectrum is known and reproduced for the first five 5 MeV in excitation in general and for the first 8 MeV in the case of I^π = 1⁺ states. Altogether the excitation energies of 80 positive-parity states are reproduced with a rms deviation of 200 keV. A calculation of radiative widths and branching ratios for γ-decay which uses effective charges and free-nucleon g-factors yields good general agreement with experiment. The need for effective g-factors is felt only in the rare cases of transitions which are governed by the isovector d_3/2 → d_5/2 M1 matrix element. The spectrum of negative parity, T = 1 states is understood in terms of the weak-coupling model while that of the T = 0 states is comprised of octupole-quadrupole phonon multiplets. Positive-parity states from outside the s-d configuration are first observed between 9.5 and 10.5 MeV excitation energy.     

Excitation of lowest electronic states of thymine by slow electrons

Excitation of lowest electronic states of the thymine molecules in the gas phase is studied by elec- tron energy loss spectroscopy. In addition to dipole-allowed transitions to singlet states, transitions to the lowest triplet states were observed. The low-energy features of the spectrum at 3.66 and 4.61 eV are identified with the excitation of the first triplet states 1₃ A′ (π → π*) and 1₃ A″ (n → π*). The higher-lying features at 4.96, 5.75, 6.17, and 7.35 eV are assigned mainly to the excitation of the π → π* transitions to the singlet states of the molecule. The excitation dynamics of the lowest states is studied. It is found that the first triplet state 1³ A′(π → π*) is most efficiently excited at a residual energy close to zero, while the singlet 2₁ A′(π → π*) state is excited with almost identical efficiency at different residual energies.     

Absorption Spectra and Thermostimulated Luminescence of Irradiated KBr Crystals with a High Content of an Na Impurity

The influence of high concentrations of the Na⁺ impurity on the photo and thermostimulated luminescence in an xirradiated KBr crystal has been studied. It is revealed that at an impurity concentration of 1 mol.% the absorption spectrum of the KBr:Na crystal possesses only the bands belonging to the (, I _A) and (F, H _A) pairs of the centers and that the thermoluminescence spectrum consists of two peaks with a maximum at 140 and 165 K.     

Atomic and molecular ions in intense ultra-fast laser fields

The interaction of a 60 fs 790 nm laser pulse with beams of Ar⁺, C⁺, H₂ ⁺, HD⁺ and D₂ ⁺ are discussed. Intensities up to 10¹⁶ Wcm^-2 are employed. An experimental z-scanning technique is used to resolve the intensity dependent processes in the confocal volume.Received: 6 January 2003, Published online: 15 July 2003PACS: 32.80.Fb Photoionization of atoms and ions - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift     

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.     

Two-photon transitions of Ag− centers in KBr

Abstract

Two-photon excitation spectra of Ag^? centers in KBr have been measured. The main excitation peak appears only with linearly polarized excitation and has been assigned to the ¹A_1g → ¹A_1g transition. Weaker structures have a polarization dependence corresponding to ¹A_1g → ¹E _g and ¹A_1g → ¹T_2g transitions.     

The collisional energy transfer between the D1Π and d3Π states of the NaK dimer induced by argon buffer gas

1 Π→X¹Σ⁺ transitions and the continuum spectrum of d³Π→a³Σ⁺ transitions of the NaK dimer in a heat pipe could be observed in the range of 500–700 nm. The collision-induced enhancement effects of the intensities I_d→a and the quenching effect of the intensities I_D→X by collisions with argon buffer gas at different pressures were measured experimentally. Based on the stationary collisional model and lifetime measurements, the quenching cross sections and cross sections for collision-induced energy transfer between the D¹Π and d³Π states could be estimated. Received: 13 January 1997/Revised version: 20 October 1997     

Photodissociation dynamics of CF3I investigated by two-color femtosecond laser pulses

We report an experimental study of the multiphoton dissociation dynamics of CF₃I performed on a home-built femtosecond laser pump-probe system, with time-of-flight mass spectrometer. The first repulsive A band and the 5pπ³7sσ υ₂=1 Rydberg state of CF₃I were accessed by one- and two-photon transitions at 267 nm, respectively, with the latter two-photon absorption followed by a further two-photon probe transition at 401 nm to the state of the parent ion. The observed signals from the CF₃ ⁺ and I⁺ fragments show similar multi-component exponential decay patterns but the former is 4 times stronger than the latter. However, the parent CF₃I⁺ signal was observed to evolve in a very different manner, decreasing sharply when probed in the first 289 fs following excitation and subsequently rising again after 860 fs to a constant level below that measured at negative pump-probe delay times when the pump and probe pulses exchange roles. This dip observed in the parent ion profile, is very different from that previously reported at shorter pump wavelengths of 264 nm or 265 nm, and is interpreted as the competition between two different ionization channels. One from the vibrationally excited υ₂=1 of the irradiated Rydberg state and the other from the dissociative vibrational origin of the same electronic state which is populated by internal vibrational relaxation.     

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.     

Dipole moment functions for electronic transitions from ion-pair states of the second tier of molecular iodine

The emission spectra caused by the transitions from the ion-pair states and f0 _g ⁺ and G1_g of the I₂ molecule are obtained by excitation of individual rovibronic levels of the molecule by the method of optical-optical double resonance. The emission spectra from the state F0 _u ⁺ populated due to collisions I₂(f) + I₂(X) are also measured. By modeling the experimental emission spectra, the dipole moment functions for the electronic transitions f _g ⁺ -B0 _u ⁺ , A0 _u ⁺ , and B″0 _u ⁺ ; G1_g-A0 _u ⁺ and B″0 _u ⁺ ; and F0 _u ⁺ -X0 _g ⁺ and a′0 _g ⁺ of the iodine molecule are reconstructed.     

NO excitation and thermal non-equilibrium within a flat plate boundary layer in an air plasma

Optical emission spectroscopy experiments are carried out by recording the radiation from the γ transitions of nitrogen monoxide in an air inductively coupled plasma in interaction with a water-cooled metallic flat plate at moderate pressure. The calibrated results allow to derive the vibrational and rotational temperatures of the NO(A ² Σ ⁺) excited state as well as its densities in the free jet and within the boundary layer by comparison with calculated spectra. Those results are compared with previous ones concerning temperatures and densities of the ground states of the majority species (N₂, O₂ and NO) that were obtained by laser techniques. As for the NO(X ² Π) ground state, vibration and rotation of the excited state are found out of equilibrium. The NO(A ² Σ ⁺) excited state is found to be populated by an energy transfer from the metastable N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}). The steady state of the plasma allows using this property to derive N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}) densities and N₂ electronic excitation temperatures. Close to the wall, a production of excited NO by a catalytic process is also considered involving N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}) as source of adsorbed atoms. The present results confirm that the kinetic temperature cannot be compared to the rotational temperature derived from optical emission spectroscopy in such plasma conditions.     

Coulomb excitation of230Th with32S,84Kr and142Nd projectiles

The Coulomb excitation measurements for the²³⁰Th nucleus with³²S,⁸⁴Kr and¹⁴²Nd projectiles are presented. The use of different projectiles allowed us to get information in the ground-state band and side bands. The energy spectrum of the ground-state band and of the lowest negative-parity band have been investigated up to the spin valueI=24⁺ andI=19^?(21), respectively. Five side bands (K ^π=0⁺, 2 ₁ ⁺ , 2 ₂ ⁺ , 1^?, 2^?) were observed also. The branching ratios for a large number of transitions in the spin regionI≦10 for π=+1 andI≦9 for π=? 1 are analysed. The full set of experimental data contains information on the mixing of the adiabatic states and on the nuclear response to the electromagnetic field ofγ-radiation. It is shown that the experimental data may be explained taking into account the coupling of the ground-β- and twoγ-bands and also of theK ^π=0^?, 1^? and 2^? negative-parity bands. An enhancement of the transitions from theγ-to theβ-band in respect to the transitions from theγ to the ground band and from theβ- to the ground band is reported. The mixing of the negative-parity bands is found to be typical for the alignment of the octupole-vibrational angular momentum. The strong spin dependence of the intrinsic matrix elements of the electric-dipole operator follows from the branching ratios of inter- and intra-band transitions from theK ^π=0^? states.     

Simultaneous cw laser oscillation on transitions of Cd+ and I+ in a hollow-cathode He-CdI2 discharge

Continuous-wave laser oscillation has been obtained on four transitions of Cd⁺ and eleven transitions of I⁺ using a hollow-cathode He-CdI₂ discharge as active medium. Laser output characteristics are similar for both Cd⁺ and I⁺ transitions, and simultaneous cw oscillation has been achieved at wavelengths ranging from blue (4416 Å Cd⁺) through green $\text{(}\text{5337}\text{5378}$ Å Cd⁺, 5407 Å I⁺), yellow $\text{(}\text{5678}\text{5761}$ Å I⁺) and orange (6127 Å I⁺) to red (6585 Å I⁺).     

Effect of carbon nanotubes on the isotropic to nematic and the nematic to smectic- A phase transitions in liquid crystal and carbon nanotubes composites

A high-resolution ac-calorimetric study on the weakly first-order isotropic to nematic (I -N and the continuous nematic to smectic-A (N -SmA phase transitions of the liquid crystal octyl-cyanobiphenyl (8CB) doped with well-dispersed multiwall carbon nanotubes (CNTs) as a function of CNT concentrations is reported. Thermal scans were performed for all samples having CNT weight fraction from f_w \phi_{{w}}^{} = 0.0005 to 0.0060 over a wide temperature range well above and below the two transitions in pure 8CB. Both the I -N and the N -SmA transitions evolve in character and have their transition temperatures qualitatively offset by ∼ 1.10 K lower as compared to that in pure 8CB for all 8CB+CNTs samples. The enthalpy change associated with each phase transition is essentially the same as that of pure 8CB and remains unchanged with increasing f_w \phi_{{w}}^{} . However, there is an evidence that the thermal transport properties of the composites differ from the pure LC upon cooling below a f_w \phi_{{w}}^{} -dependent temperature within the nematic phase. In addition, a new C_p feature is resolved for intermediate f_w \phi_{{w}}^{} samples that appears to be correlated to this onset temperature.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.