Kr2F1 and Kr12 radiative lifetime measurements

Atomic krypton was excited in presence of SF₆ by an intense electron beam. The radiation emitted by the Kr₂F¹(²B₂→ A₁) transition was studied at 430 nm using time resolved spectroscopic techniques. The radiative lifetimes of Kr₂F¹ and of Kr¹₂ were found to be 200 ns and 270 ns respectively.     

Kinetic studies of Kr2 Cl in electron-beam excited gas mixtures

Gas mixtures containing atomic krypton and carbon-tetrachloride were excited using intense electron beam pulses. The fluorescence produced by Kr₂Cl¹ was studied using time-resolved spectroscopic techniques. The lifetime (470 ns) and the quenching rate constants of Kr₂Cl¹ were deduced from the measurements.     

Evidence of KrF1 broad band continuum emission at 400 nm

Broad band emission of KrF¹ centered at about 400 nm was observed in various mixtures containing Kr and fluorinated compounds. This emission was resolved against the more intense Kr₂F¹ broad band emission at the same wavelengths due to its temporal behaviour and its different pressure dependence. Its radiative lifetime is 16 ns and it is tentatively ascribed to the 3 ²∑⁺ → 1 ²Π transition.     

He/Ar/Kr/F2混合气体中准分子KrF*和Kr2F*的动力学研究

本文用时间积分谱的方法研究了快放电激励下He/Ar/Kr/F₂混合气体中Kr₂F^*的动力学,探讨了Kr₂F^*形成的通道特性,理论分析和实验结果表明,在快放电激励下,三体碰撞过程KrF^*+Kr+M→Kr₂F^*+M是形成Kr₂F^*的主要通道,而置换反应ArF^*+Kr→KrF^*+Ar又能有效地产生KrF^*。实验测量了Kr₂F^*形成的有关速率常数。 关键词：     

Charge-transfer reactions in clusters excited with synchrotron radiation

Charge-transfer reactions are observed in a photoluminescence study of NF₃\rm NF_3-doped free krypton clusters. They show up in emissions from Kr⁺F^-\rm Kr^{+}F^{-}free excimers ejected from the clusters, and from excited Kr₂⁺F^-\rm Kr_2^{+}F^{-}and Kr₂⁺(NF₃)_m^-{\rm Kr}_2^{+}({\rm NF}_3)_m^{-} (m 3(m\geq 1) solvated in the clusters. The results show that reaction dynamics in clusters differs considerably from that in the gas and solid phases.     

A KrF fast discharge laser in mixtures containing NF3, N2F4 or SF6

A fast discharge KrF laser system (λ = 248.5 nm) has been operated at 25 mJ/pulse, 3.0 MW peak power in high pressure He: Kr: fluoride mixtures containing low concentrations of both krypton and the fluorine donors N₂F₄, NF₃ and SF₆. Lasing action is reported for the first time in N₂F₄ and SF₆ with optimum energy output at 750 and 160 mJ/l respectively.     

Emission and excitation spectra of Bi2Ge3O9:Eu3+

The emission and excitation spectra of the Bi₂Ge₃O₉:Eu crystal are observed at 77 K and 297 K. The spectra contain groups of sharp lines which are attributed to the transitions within 4f⁶ (Eu³⁺) configuration. The numbers of Stark splitting of terminal levels of transitions from ⁵D₀ and ⁷F₀ multiplets indicate that Eu³⁺ substitutes for Bi³⁺ in Bi₂Ge₃O₉. Tentative assignment of Stark levels of ⁷F_0-4 multiplets is made to crystal quantum numbers of C₃ symmetry which represents the site symmetry of Bi³⁺ in Bi₂Ge₃O₉. The following set of values of crystal field parameters of the C₃ point group is found to give the best overall agreement between the observed energy levels and the calculated levels: B²₀ = -533.84 cm^-1, B⁴₀ = 1085.99 cm^-1, Re(B⁴₃) = 327.57 cm^-1, Im(B⁴₃) = 75.209 cm^-1, B⁶₀ = 185.02 cm^-1, Re(B⁶₃) = - 68.475 cm^-1, Im(B⁶₃) = - 300.45 cm^-1, Re(B⁶₆) = 137.24 cm^-1 and Im(B⁶₆) = 882.29 cm^-1.     

The High-Resolution ν5 Band of Jet-Cooled Si2F6

Vibration-rotation spectra of the parallel ν₅ band of hexafluorodisilane have been measured in a supersonic free jet with 0.001 cm⁻¹ resolution. Three isotopic species, ^28,28Si₂F₆, ^28,29Si₂F₆, and ^28,30Si₂F₆, have been studied. The effect of internal rotation is not observed, indicating that the splitting is smaller than our spectral resolution. A very weak parallel band observed with a slight red shift from the ν₅ fundamental band has been assigned tentatively to the (ν₄ + ν₅)-ν₄ hot band.     

Infrared diode laser spectroscopy of FCO: The ν1 and ν2 bands

The ν₁ (CO stretching) and ν₂ (CF stretching) bands of the FCO radical were observed with Doppler-limited resolution by an infrared diode laser spectrometer with Zeeman and source modulation. The FCO radical was generated by a 60-Hz discharge in one of the following three gas mixtures: O₂ + C₂F₄, CO + SF₆, and CO + C₂F₄, all diluted with He. The observed spectra were analyzed to determine the rotational constants, the centrifugal distortion constants, and the spin-rotation interaction constants. The band origins, 1861.6372(1) and 1026.1283(1) cm^?1 [with standard errors in parentheses], which were obtained, were found to agree well with matrix data, 1857 and 1023 cm^?1, respectively. The assignment of the observed spectra to the FCO radical was further supported by observing the ν₁ band of F¹³CO, which was obtained from ¹³CO and SF₆. The molecular structure and the force field of FCO are briefly discussed by using molecular constants obtained from the observed spectra.     

Racah and Judd-Ofelt parameters for Pr3+, Nd3+, and Er3+ ions in a laser liquid

The values of the Slater-Condon (F₂, F₄, F₆), Racah (E¹, E², E³) and Lande ξ₄f coefficients the nephelauxetic ratio (β), the bonding parameter (σ), and the Judd-Ofelt intensity (T_λ) parameters have been calculated from the reported absorption spectra of Pr³⁺, Nd³⁺, and Er³⁺ ions in an aprotic solvent SeOCl₂ acidified with antimony pentachloride. The nature of the bonding is suggested to be covalent for praseodymium, neodymium and erbium ions in the laser liquid in view of the magnitude of the respective bonding parameters.     

Er3+，Tm3+共掺的NaY(WO4)2晶体的光谱分析和上转换发光

在室温下，测量了Er:Tm:NaY(WO₄)₂晶体的吸收光谱、激发光谱、发射光谱以及上转换发光，并运用J-O理论对测量的结果进行了计算，得出了Er:Tm:NaY(WO₄)₂晶体的强度参数.报道了Tm，Er离子间特殊的能量传递和相关上转换，解释了离子间的能级跃迁过程.同时，对于Er增强Tm离子近红外发光的特性也作了充分研究. 关键词： 4)₂晶体')" href="#">Er:Tm:NaY(WO₄)₂晶体 吸收光谱 发射光谱 激发光谱 上转换     

Tm3+离子掺杂的钨酸钇钠晶体中浓度猝灭效应的研究

测量了Tm³⁺离子不同浓度(0.5at.%, 3 at.%, 5 at.%)掺杂的NaY(WO₄)₂晶体在800nm激光二极管激发下的上转换发射光谱.结合吸收谱、荧光谱和由Judd-Ofelt理论计算的光谱参数，详细分析了Tm³⁺:NaY(WO₄)₂晶体中上转换能量传递机理和离子浓度对上转换发射的影响.讨论了四种影响上转换发光效率的离子间相互作用机理：³H₅+¹G₄→³H₆+¹D₂，³H₅+³H₅→³H₆+³F₃，¹G₄+³H₆→³F₄+³F₃，¹G₄+³H₆→³F₃+³F₄，并根据Miyakawa-Dexter理论定量计算了各过程的发生概率.论证了交叉弛豫和共协上转换等浓度猝灭效应是影响Tm³⁺离子蓝色上转换荧光发射效率的主要因素. 关键词： 3+离子')" href="#">Tm³⁺离子 4)₂晶体')" href="#">NaY(WO₄)₂晶体 上转换 浓度猝灭     

Adsorption-desorption studies using ESD of CCl2F2, C2H2F2 and C2F6 on tungsten

The behavior of the desorbing F⁺ ion current from electron bombarded CCl₂F₂, C₂H₂F₂ and C₂F₆ adsorbed on tungsten has been used to investigate the processes of adsorption and desorption of these gases. For tungsten near room temperature, measurements of the F⁺ ion current as a function of electron bombardment time indicated very similar or even identical F⁺-yielding adsorbed species resulting from adsorption of either CCl₂F₂ or C₂H₂F₂ and widely different species from C₂F₆. Cl⁺ ions were also observed to desorb from CCl₂F₂ ad-layers. The behavior of the Cl⁺ ion current with time during electron bombardment indicated electronic conversion between adsorbed binding modes. Complementary investigations on the interaction of CCl₂F₂, C₂H₂F₂ and C₂F₆ with tungsten were carried out by thermal desorption experiments in which the F⁺ ion signal was used to observe the coverage decrease of the F⁺-yielding species. The experiments were performed at tungsten temperatures in the 1200–1600 K range. It was concluded that the F⁺-yielding adsorbed species from CCl₂F₂ and C₂H₂F₂ were strongly bound to the tungsten surface. The F⁺-yielding species from C₂F₆ were found to be weakly bound. From a comparison of the ESD and thermal desorption results, the possibility of dissociative adsorption as well as the nature of the adsorbed species is discussed.     

Etude des transitions de phases des composes Rb2KMO3F3, Cs2KMO3F3 et Cs2RbMO3F3 (M = Mo,W)

Crystallographic, micro-D.T.A., dielectric and pyroelectric measurements have been performed for the Rb₂KMO₃F₃, Cs₂KMO₃F₃ and Cs₂RbMO₃F₃ (M = Mo, W) compounds. Two types of transitions have been detected : the first one, for Rb₂KMoO₃F₃ at low temperature, is due to the disappearance of the superstructure detected for Rb₃MoO₃F₃α, the second one is of ferroelectric - paraelectric type (Rb₂KMO₃F₃ and Cs₂RbMO₃F₃ ; M = Mo, W). The transition temperatures have been compared vs the size of the alcaline ions and the nature of the M-O bonds. The increase of the transition temperatures from the A₂A'MO₃F₃ to the A₃MO₃F₃ compounds is likely due to the simultaneous presence of the A⁺ cations in the former ones in 6 and 12 coordination sites.     

ANISOTROPY OF OPTICAL ABSORPTION INTENSITY IN Tm3+ DOPED YVO4 CRYSTALS

Seven absorption group-bands (¹D₂, ¹G₄, ³F₂, ³F₃, ³H₄, ³H₅, ³F₄) of Tm³⁺ in YVO₄ single crystals have been observed in the orientation absorption spectra recorded in the spectral range from 200 to 4000 nm at 300K. The integrated absorption cross section for each group-band was accurately evaluated. On the assumption that the anisotropy of this uni-axial crystal is small, the Judd-Ofelt theory was extended for the calculation of 4f-4f transition intensities of Tm³⁺ in YVO₄. Two sets of phenomenological intensity parameters were derived from a least-squares-fit procedure. For c-axis cut sample we have Ω₂=10.18 (10^-20cm²), Ω₄=1.96 (10^-20cm²), Ω₆=0.75 (10^-20cm²).For a-axis cut sample we have Ω₂=8.20 (10^-20cm²), Ω₄=2.47 (10^-20cm²), Ω₆=0.91 (10^-20cm²). The anisotropy of the optical absorption intensities of Tm³⁺:YVO₄ was theoretically analyzed in detail.     

Optical amplification properties of Dy3+-doped Gd2SiO4, Lu2SiO5 and YAl3(BO3)4 single crystals

Comparative investigation of the optical amplification properties of dysprosium doped Gd₂SiO₅, Lu₂SiO₅ and YAl₃(BO₃)₄ single crystals was performed in a pump-and-probe experiment. High power laser pulses at 475 nm were used as the pump source in order to strongly populate the ⁴F_9/2 level of the Dy³⁺ ions due to ground state absorption. Low signal beam cw radiation at 574 nm was used as the probe beam to stimulate the emission associated with the ⁴F_9/2→⁶H_13/2 electronic transition of the Dy³⁺ ions. The process was modelled as a three levels system, and their populations were analysed and simulated in order to study the gain dynamics. Positive optical gain was observed and compared in these crystals. These results confirmed that among the systems studied the Dy³⁺-doped YAl₃(BO₃)₄ single crystal can be considered as a good candidate to develop an optical amplifier employing the ⁴F_9/2→⁶H_13/2 transition at around 574 nm which is the first step to consider as laser active media.     

Multiple fluorescence and the electronic relaxation processes of coronene vapor: The fluorescence from the S1, S2, and S3 states

Fluorescence and excitation spectra of coronene vapor have been measured under different conditions. Weak emission which can be regarded as the fluorescence from the third excited singlet state, S₃(¹E_1u), was observed in addition to the S₁(¹B_2u) and S₂(¹B_1u) fluorescence. The observed S₂ and S₃ fluorescence are substantially different from those reported previously for coronene vapor. Addition of oxygen resulted in significant decrease of the S₁ fluorescence intensity, but did not affect the S₂ fluorescence intensity, indicating the faster decay rate of the S₂ state than that of S₁. Excitation energy dependence of the S₁, S₂ and S₃ fluorescence quantum yields (Φ_F(S₁), Φ_F(S₂) and Φ_F(S₃), respectively) revealed that Φ_F(S₁) decreases with increasing excitation energy, while Φ_F(S₂) and Φ_F(S₃) increase significantly. The quantum yield ratios, Φ_F(S₂)/Φ_F(S₁) and Φ_F(S₃)/Φ_F(S₂), obtained as a function of excitation energy are correlated with the ratios of the relative internal conversion rates.     

Optical absorption spectrum of PrCl3 complexes in solution

Optical spectral studies of Pr³⁺ in PrCl₃ complexes with MgCl₂, CaCl₂, CdCl₂ and NH₄Cl have been carried out, and the second derivative spectra of these five Pr³⁺ complexes are reported. From the observed features of the ³P₂ and ¹D₂ bands, crystal field (A₂₀, A₄₀) parameters were evaluated assuming C_3h symmetry for Pr³⁺ in these complexes. The Slater-Condon(F₂, F₄ and F₆), configuration interaction (α, β) and spin-orbit (ξ_4?), Racah (E¹,E² and E³), nephelauxetic (β), bonding (δ) and Judd-Ofelt (T₂, T₄ and T₆) intensity parameters are evaluated. Theoretical estimates of spectral intensities calculated from Judd-Ofelt and electric (S_ed)-magnetic (S_md) dipole linestrength methods are in good agreement with the observed values. The radiative lifetimes of elctronic excited states ³P₁, ³P₀, and ¹D₂ of Pr³⁺ in these five different hosts have been theoretically estimated.     

Eu photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2-B2O3-PbO2 glasses system

In this work, Eu³⁺-doped lead borosilicate glasses (SiO₂-B₂O₃-PbO₂) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500 °C show a precipitated crystalline phase with sizes 11 and 21 nm, respectively. Besides, as the temperature increases from 350 to 300 K a strong Eu³⁺ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu³⁺ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu³⁺ transitions ⁵D₀→⁷F₂, at 612 nm, ⁵D₀→⁷F₁, at 595 nm, and ⁵D₀→⁷F₀, at 585 nm. It was also observed that the ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ PL bands at 655 and 700 nm, respectively, show a continuous decrease in intensity as the temperature increases.     

Structures and luminescence properties of Yb3＋ in the double perovskites Ba2YB＇O6 （B＇=Ta5＋, Nb5＋） phosphors

The Yb³⁺ doped Ba₂YB'O₆ (B'=Ta⁵⁺, Nb⁵⁺) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb³⁺:Ba₂YB'O₆ (B'=,Ta⁵⁺, Nb⁵⁺) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO₆ or NbO₆ centre with large Stokes shift. The Yb³⁺ doped into these hosts are situated at Y³⁺ sites of cubic symmetry (O_h). The experimental energy levels of Yb³⁺ in Ba₂YTaO₆ and Ba₂YNbO₆ were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb³⁺:Ba₂YB'O₆(B'=Ta⁵⁺, Nb⁵⁺) from (²F_5/2)Γ₈^- to the low-energy states were calculated.