Average excited state lifetimes in 73Br

Lifetimes in the region of 10^?16 s have been measured for excited states between 4 and 6.6 MeV in ⁷³Br. The states were produced by the β⁺(EC) decay of a mass-separated source of ⁷³Kr, and they decayed by the emission of protons or γ-rays; their lifetimes were measured by the particle X-ray coincidence technique. The data yield information on both γ-ray and proton partial widths as well as on the level density, a level density parameter-a = 13.7 MeV^?1 is obtained. With the level widths so determined, a statistical model calculation yields excellent agreement with the delayed proton spectrum if a smooth gaussian β-strength function is employed. It is concluded, however, that without the lifetime data, β-strength function information could not have been reliably extracted.     

Delayed neutrons and high-energy γ-rays from decay of 87Br

Delayed neutrons and high-energy γ-rays following decay of ⁸⁷Br have been studied to characterize the β-decay to and the decay of neutron unbound levels in ⁸⁷Kr. The principal part of the neutron spectrum appears due to some 20–30 individual transitions and for seven of these, decay by γ-ray emission has been demonstrated. The β-strength function derived from these data and the decay scheme at lower energies is dominated by a broad resonance located near the neutron binding energy which can be identified with the main strength of a single-particle transition. The fluctuations in the reduced β-transition probabilities are found to be in accord with the Porter-Thomas distribution and the observed level density just above the neutron binding energy is consistent with the Gilbert and Cameron prediction after accounting for fluctuation in the β-decay transition probabilities.     

Emission spectrum of concentrated dye solutions excited by high-power laser radiation

Emission spectra of concentrated (~10¹⁸–10¹⁹ cm^–3) ethanol solutions of Rhodamine C excited by high-power (~10²⁵–10²⁶ cm^–2s^–1) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm^–1). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.     

Study of VUV emission and γ-ray responses of Nd:BaF2 scintillaotor

Nd³⁺ 1%, 5% and 10% doped BaF₂ single crystals were grown by the micro-pulling down method. Photoluminescence properties, including excitation and emission spectra and luminescence decay were measured under synchrotron radiation excitation at the Superlumi station in HASYLAB at DESY (Hamburg, Germany). The Nd³⁺ related 5d-4f emission lines peaking around 180 nm, 230 nm, and 260 nm, identified as the 5d–⁴I_j, 5d–⁴F_j, and 5d–²G_j transitions, were observed under 140–168 nm excitation. In photoluminescence decay under the 160 nm excitation, the dominant component decay time is about 12, 2.5 and 1.2 ns for Nd³⁺ 1%, 5% and 10% concentration, respectively. The decay time shortening is explained by the concentration quenching effect. Transmittance of Nd1% sample is about 80% for wavelengths above 185 nm. Finally, gamma-ray responses, non-proportionality and energy resolution of Nd1% sample were compared with the undoped BaF₂ scintillator. The light yield of the Nd1%:BaF₂ is about 93% of that of undoped BaF₂. ^©2009 Elsevier Ltd. All rights reserved.     

The impurity-induced luminescence of RbMnF3

The impurity-induced luminescence of RbMnF₃ has been studied in the temperature range, 4–120 K. Multimagnon sidebands of impurity-induced Mn²⁺ emission lines have been detected spanning the spectral range, 5515–5960 Å. The broad emission bands, which peak at 5750 Å and 6440 Å, have been attributed to phonon-assisted transitions from two impurity-induced Mn²⁺ traps of different depths. Pulsed luminescence measurements indicate that the quenching of the shallow trap emission is by a thermal activation to the E1 exciton level whereas the quenching of the deeper trap emission is by a multiple phonon decay. The coupling between Mn²⁺ ions is strong enough to support a detectable transfer of excitation between these two traps.The results of this research also include the observation in absorption of the E1 exciton line and its 1-magnon and possible 2-magnon sidebands.     

Steady‐State and Time‐Resolved Emission Studies of 6‐Methoxy Quinoline

Abstract

Steady‐state absorption, fluorescence excitation, and emission spectra of 6‐methoxy quinoline (6‐MQ) were measured at room temperature in cyclohexane, dioxane, ethanol, acetonitrile, water, and water–dioxane solvents. Absorption spectra of cyclohexane, n‐hexane, and isopentane solutions show resolved vibronic structure at room temperature. However, the excitation spectrum of cyclohexane solution is structureless and is found to be emission wavelength dependent, indicating the formation of at least two distinct species in the ground state. Similar behavior was observed in dioxane and water–dioxane solutions. For all other solutions, the fluorescence excitation spectrum of 6‐MQ was found to be the same for different emissions. Emission of 6‐MQ in all solvents consisted of two bands with their maxima around 355 nm (I) and 430 nm (II), the actual positions and the relative intensities being dependent on the solvent used. The bands I and II were respectively attributed to normal and protonated/H‐bonded species of either ¹L_a or ¹L_b states or mixed (¹L_a/¹L_b) state of ππ* character. Fluorescence decay of this dye in all solvents monitored over each emission maximum showed biexponential behavior, and the analysis yielded two different lifetime components for each emission band. The short and long fluorescence decay components were respectively in the range of 0.30–3.00 ns and 18–20 ns. The observed emission characteristics coupled with the nature of the fluorescence polarization spectra and two different decay components for each emission suggest the existence of two different conformers having two different excited electronic states.     

Spectral properties of Pr3+ ions in Bi2(MoO4)3 crystal

A Bi₂(MoO₄)₃ single crystal doped with Pr³⁺ ions has been grown by the Czochralski technique. The polarized absorption and fluorescence spectra as well as the fluorescence decay curve of Pr³⁺ ions in the crystal were measured at room temperature. The spectroscopic parameters, including the Judd–Ofelt intensity parameters Ω_t (t=2, 4, and 6), spontaneous emission probabilities, fluorescence branching ratios, radiative lifetimes, stimulated emission cross sections, and fluorescence quantum efficiencies, were calculated. The spectral properties related to laser performance of this crystal were analyzed. The ¹ D ₂ multiplet of the crystal may be a good upper level for a solid-state laser.     

Production of Λ hypernuclei in π+ A interactions

The production of Λ hyperons in π⁺ A interactions is studied on the basis of the intranuclear-cascade model, and the excitation-energy, momentum, angular-momentum, charge, and mass distributions of the ensemble of product hypernuclei are determined. The decay of excited hypernuclei via particle emission and fission is considered. It is shown that, for the production of heavy Λ hypernuclei, the optimal momentum of the incident π⁺ meson is about 1 GeV/c. The cross section of the channel in which heavy-nucleus decay induced by a π⁺ meson is accompanied by the emission of a K ⁺ meson is estimated, and it is proposed to use the reaction (π⁺, K ⁺ f) in measurements of the fission barrier in hypernuclei and of their level density.     

VUV-UV-visible luminescence of Nd3+, Er3+ and Tm3+ in LiLuF4 single crystal host

An overlook of absorption and luminescence characteristics of Nd³⁺, Er³⁺ and Tm³⁺ centers in LiLuF₄ single crystal is provided. Single crystal doped with the mentioned RE ions were prepared by micro-pulling-down technique in the form of few cm long rods with the diameter of about 2 mm. Excitation and emission spectra and fast decay kinetics in VUV spectral region were measured at SUPERLUMI station at synchrotron DESY, Hamburg and characterization was further completed in UV-visible region at conventional spectrophotometers. Observed absorption and emission peaks are ascribed to the 5d–4f and 4f–4f optical transitions in the doped rare earth ions. Concentration dependence of the decay kinetics is discussed.     

Impact of Tensor Interaction on Beta-Delayed Neutron Emission from Neutron-Rich Nickel Isotopes

The Skyrme energy density functional including tensor interaction is used to describe microscopically multineutron delayed-neutron emission accompanying beta decay of even–even neutron-rich nickel isotopes of mass number in the range of A = 74?80. The respective calculations are performed in the quasiparticle random-phase approximation with allowance for the two-phonon components of the wave function for states of the daughter nucleus. The properties of the lowest quadrupole excitation of ^74,76,78,80Ni are also studied. It is shown that a decrease in the strength of neutron–proton tensor interaction leads to a substantial hindrance of beta decay and to an increase in the probability for delayedneutron emission.     

Photoluminescence of Pb2+-doped SrHfO3

Pb²⁺ excitation and emission spectra and decay kinetics in SrHfO₃ host are measured within 10–350 K temperature interval. Temperature dependence of decay times is fit by the phenomenological model describing the dynamics of the lowest excited state of Pb²⁺ ion. The best fit provided corresponding quantitative parameters of the model. Suitability of the Pb-doped SrHfO₃ for phosphor and scintillator application is discussed.     

Effect of pressure on luminescence properties of Sm3+ ions in potassium niobate tellurite glass

Emission spectra and decay properties of the ⁴G_5/2 level of Sm³⁺ ions in TeO₂+K₂O+Nb₂O₅ glass have been measured as a function of pressure upto 14.6 GPa at room temperature. A progressive red shift in the barycentres of ⁴G_5/2→⁶H_J (J=9/2, 7/2 and 5/2) emission bands and increase in splitting of these bands have been observed with increasing pressure. The luminescence decay profile of the ⁴G_5/2 level at ambient condition shows a nearly single exponential nature and with increase in pressure it becomes gradually non-exponential associated with a decrease in lifetime. The non-exponential decay curves are well-fitted to the Inokuti–Hirayama model for S=6, indicating that the interaction for cross-relaxation energy transfer between Sm³⁺ ions is of dipole–dipole type. The results obtained after release of pressure reveal that there is a small hysteresis.     

Vacuum ultraviolet 5d14f9-4f10 emission of Ho3+ ions in alkaline-earth fluorides

Time-resolved emission and excitation spectra as well as emission decay kinetics of CaF₂, SrF₂, BaF₂ doped with HoF₃ were investigated. Intensive emission bands near 168 nm, having long decay time, are caused by the spin-forbidden transitions from the 5d¹4f⁹ high-spin states to the ground ⁵I₈ states of Ho³⁺ ions. Weak spin allowed 5d¹4f⁹(low-spin)-4f¹⁰ emission band at 158 nm was observed only in CaF₂–Ho crystals. Spin allowed and spin-forbidden excitation bands were observed near 166 and 155 nm, respectively, in all studied crystals. Fast component of spin-forbidden emissions due to multiphonon relaxation to low-lying 4f¹⁰ Ho³⁺ level also was observed for all crystals.     

Luminescence and decay times of CsI:In+

Luminescence spectra of single crystals of CsI:In⁺ excited in the A(304 nm), B(288 nm), C(268 nm) and D(257 nm) absorption bands have been studied in the temperature range 4.2–300 K. Excitation in the A band at 4.2 K gives rise to the principal emission at 2.22 eV accompanied by a partly-overlapping weak band at 2.49 eV. An additional emission band at about 2.96 eV is observed on excitation in the B, C or D bands. Yet another emission band located at 2.67 eV is excited only in the D band. The relative intensities of the bands are very sensitive to excitation wavelength as well as to temperature. The origin of all these bands is assigned in terms of a model for the relaxed excited states (RES). All the luminescence spectra were resolved into an appropriate number of skew-Gaussian components. Moments analysis leads to a value of (1.35 ± 0.02) × 10¹³ rad s^-1 for the effective frequency (ω_eff) of lattice vibrations coupled to the RES. At the lowest temperature, the radiative decay times of each of the intracenter emission bands (2.22, 2.49 and 2.96 eV) show a slow decay ( ～ 10–100 μs) and a fast decay ( ～ 10–100 ns). The 2.96 eV band, which is assigned to an emission process which is the inverse of the D-band absorption, exhibits a single decay mode ( ～ 10 μs). The intrinsic radiative decay rates (k₁, k₂), the one-phonon transition rate (K) and the second-order spin-orbit splitting (D) for the RES responsible for the principal emission are: k₁ = (6.0±-0.3)×10³ s^-1, k₂ = (1.33±-0.06)×10⁵ s^-1, K = (2.4±-0.4)×10⁷ s^-1 and D = (13.8±-0.5) cm^-1.     

Lifetime measurement in the β system (c1Φ-a1Δ) of TiO

The radiative lifetime of the v′ = 0 level of the c¹Φ state of TiO has been measured from observations on fluorescent decay of a single rotational level, following excitation by laser radiation. The value is τ₀ = 17.5 ± 1.0 nsec. From this is derived a transition probability of 5.71 × 10⁷ sec^?1 and an emission f value of 0.270. Transition probabilities for the other bands in the β system have been calculated.     

On the possibility of stimulated emission in GaP : N

The luminescence decay times of NN_i-pair emission are found to decrease when the photoexcitation density is increased from several W/cm² to 10⁶–10⁷ W/cm². For lightly N-doped GaP, the reduction is typically from 3000 to 30 nsec (A-line, low temperature); for heavily N-doped GaP it is from about 1000 nsec to a few nanoseconds. From this decay time reduction the onset of a new recombination mechanism is concluded. No mechanism is likely to explain previously reported high gain values for GaP : N.     

Internal bremsstrahlung of strongly interacting charged particles

A universal theoretical model intended for calculating internal-bremsstrahlung spectra is proposed. In this model, which can be applied to describing nuclear decays of various type (such as alpha decay, cluster decay, and proton emission), use is made of realistic nucleus–nucleus potentials. Theoretical internal-bremsstrahlung spectra were obtained for the alpha decay of the ²¹⁴Po nucleus, as well as for the decay of the ²²²Ra nucleus via the emission of a ¹⁴C cluster and for the decay of the ¹¹³Cs nucleus via proton emission, and the properties of these spectra were studied. The contributions of various regions (internal, subbarrier, and external) to the internal-bremsstrahlung amplitude were analyzed in detail. It is shown that the contribution of the internal region to the amplitude for internal bremsstrahlung generated in nuclear decay via proton emission is quite large, but that this is not so for alpha decay and decay via cluster emission. Thus, a process in which strong interaction of nuclear particles affects the internal-bremsstrahlung spectrum if found.     

Two-proton radioactivity search

Two-proton radioactivity, a spontaneous breakup of elements with emission of two protons, was predicted to exist near the proton drip line by V.I. Goldansky long time ago. The recent theoretical and experimental progress in a search for such an exotic nuclear decay is reviewed. In theory, the new three-body model which treats two-proton radioactivity as a genuine three-particle nuclear decay is considered. In experiment, the first evidence for two-proton decay of ⁴⁵Fe is described. Four atoms of ⁴⁵Fe, produced at the fragment separator of GSI, decayed via particle emission with a total energy of 1.1(1) MeV and a half-life of 3.2 _?1.0 ^+2.6 ms. A possible experiment for a direct observation of two-proton emission from the ground state of ¹⁹Mg is considered for its decay in-flight. The half-life of ¹⁹Mg, as well as proton-proton correlations, might be derived from the distribution of the ¹⁹Mg decay vertices extrapolated from the measured trajectories of all fragments.     

Spectroscopic and nonlinear characteristics of anthracene-containing silicon-organic polymers in solution

Spectroscopic characteristics, i.e. absorption, fluorescence, fluorescence excitation spectra, fluorescence decay time, fluorescence polarization degree of novel silicon-containing organic polymers including main chain anthracene groups were investigated. Three kinds of emission spectra were revealed and assigned to polaron–exciton, anthracene and anthracene dimer. The measured fluorescence polarization spectra gave evidence of directed excitation energy migration along the disordered polymeric chain. Strong quenching of anthracene fluorescence during the polaron–exciton lifetime was interpreted as a result of the interaction between two excitations that causes anthracene anion-radical formation. The third-order nonlinear susceptibility of the polymers in solution measured by the Z-scan technique at 1054 nm is 190×10⁻¹⁴ cm² W⁻¹.     

Analysis of Energy Transfer and Concentration Quenching in Sm3+-Activated Borate GdB3O6 Phosphors by Means of Fluorescence Dynamics

This article reports on the optical properties of Sm³⁺-activated GdB₃O₆ phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd³⁺ to Sm³⁺ and the concentration quenching of the Sm³⁺ ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd³⁺ to Sm³⁺ is confirmed. The concentration quenching of the Sm³⁺ ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm³⁺ ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm³⁺⁴G_5/2 level exhibiting a buildup and decay process also confirm the energy transfer from Gd³⁺ to Sm³⁺ and between Sm³⁺ ions.