Sensitive method for the determination of F attached to aerosol particles in a PET centre

A new grab sampling method has been developed for the measurement of ¹⁸F attached to aerosol particles. It is based on direct β-counting of filtered aerosol sample over successive time intervals by an end-window Geiger–Müller counter. The effect of the progeny of radon and thoron on the β-counting rate is separated by analysing the decay curve. The defined solid angle absolute counting was used to evaluate the efficiencies for ¹⁸F and for the progeny of radon and thoron one by one. Absolute activity concentration of ¹⁸F can be determined with less than 10% systematic error. Glass-fibre filter and high sampling flow rate are applied, leading to a detection limit for ¹⁸F of less than 1 Bq m⁻³. The method was tested under different circumstances in the PET centre of University of Debrecen, Hungary.     

Measurement of fluorine total concentration in dental enamel using fast-neutron activation

Fluorine which is present in dental enamel, at the level of a few tens to a few hundred ppm, plays an important role in the behaviour of this tissue. Therefore its quantitative determination is of interest for particular studies of the dental system. We present a nuclear nondestructive method to determine the total fluorine content in dental enamel by cyclotron-produced fast-neutron activation. The ¹⁹F(n, 2n) reaction leads to ¹⁸F which is a β⁺ emitter with a 109.8 min half-life. The irradiated sample activity is measured by detecting in coincidence the annihilation photons. A fluorine standard is used for calibration. The detection limit is of the order of 1 ppm, while the reproducibility is better than 95%.     

Feasibility study of in-beam polarization of fluorine

The feasibility of in-beam polarization of nuclear spin in F⁺ beams was studied. It was demonstrated that metastable atomic fluorine could be optically pumped on the closed transition (3s ⁴P_5/2→3p ⁴D_7/2) at 686 nm. The metastable production efficiency in sodium vapor was measured using optical depopulation pumping of the metastable on the (3s ⁴P_5/2→3p ⁴D_5/2) transition at 678 nm. At low helium density, 0.24 (+0.16/−0.03) of the reionized beam was derived from metastables, implying an ion beam polarization of 24% would be feasible if the metastables were fully polarized. The hyperfine structures of the 3s ⁴P_5/2, 3p ⁴D_5/2 and 3p ⁴D_7/2 states in ¹⁹F were measured via laser-induced fluorescence and modulated optical depopulation pumping. Based on these results, a scheme is suggested for polarizing ²⁰F.     

Optically active Er–Yb codoped Y2O3 films produced by pulsed laser deposition

Optically active Er³⁺:Yb³⁺ codoped Y₂O₃ films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y₂O₃ targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 10²¹ at cm^− 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb³⁺ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 10²⁰ at cm^− 3 and total rare-earth concentration ≈ 1.8 × 10²¹ at cm^− 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

Spectroscopic evidence of inhomogeneous distribution of Nd in YVO4, YPO4 and YAsO4 crystals

Nd³⁺ : YVO₄ is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd³⁺ in three zircon type crystals YMO₄ (M=V, As, P). In particular, Nd³⁺ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO₄, single crystals containing 7 ± 1 × 10¹⁸ Nd³⁺ ions/cm³, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd³⁺ ions. Nd³⁺ ions are found to be inhomogeneously distributed in tetragonal D_2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd³⁺ ions are gathered in Nd³⁺–Nd³⁺ pairs for 7.2 ± 0.2 × 10¹⁹ Nd³⁺ ions/cm³.     

Determination of upper and lower limits combining different experimental results

This paper discusses how to combine different experimental results in order to obtain upper or lower limits of physical quantities in the case of null experiments. Reanalyzing some published results, half-life limits for p → e⁺π⁰, p → K⁺, and for the ⁷⁶Ge ββ(0ν)-decay to the ground state of ⁷⁶Se were determined as 5.7 × 10³², 1.4 × 10³² and 2.5 × 10²⁴ yr, respectively, at 90% Confidence Level. The Bayesian approach is adopted using a step function as the prior-probability density function of the decay constant.     

Effect of radiation trapping on the emission properties of Er: I13/2 → I15/2 transition in oxide glasses

The effect of radiation trapping on the emission properties of Er³⁺-doped tellurite and phosphate glasses has been investigated as the function of sample thickness and doping concentration. It was found that radiation trapping exists generally in two glass matrices, even at low doping concentration (0.1 mol% Er₂O₃). The larger effect of radiation trapping in tellurite glasses compared with phosphate glasses is due to its larger emission cross-section at 1.5 μm band and the spectral overlap between the emission and absorption spectra of Er³⁺: ⁴I_13/2 ↔ ⁴I_15/2transition. Due to radiation trapping, the measured lifetime of the Er³⁺: ⁴I_13/2 level in tellurite glasses increases by about 11–37% with increasing the sample thickness at the different erbium doping concentration, while 6–17% for phosphate glasses. And the full-width at half maximum of fluorescence (FWHM) of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses increased by about 15–64% with increasing the sample thickness, while 11–55% for phosphate glasses. It caused a high overestimation on the figure of merits (FOM) for amplifier bandwidth (σ_e × FWHM).     

Synthesis and the luminescent properties of europium-activated Ca2SnO4 phosphors

The synthesis and photoluminescent (PL) properties of calcium stannate crystals doped with europium grown by mechanically activated in a high energy vibro-mill have been investigated. The characteristics of Ca₂SnO₄:Eu³⁺ phosphors were found to depend on the amounts of europium ions. The XRD profiles revealed that the system, (Ca_1−xEu_x)₂SnO₄, could form stable solid solutions in the composition range of x = 0–7% after being calcined at 1200 °C. The calcined powders emit bright red luminescence centered at 618 nm due to ⁵D₀ → ⁷F₂ electric dipole transition. Both XRD data and the emission ratio of (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) reveal that the site symmetry of Eu³⁺ ions decreases with increasing doping concentration. The maximum PL intensity has been obtained for 7 mol% concentration of Eu³⁺ in Ca₂SnO₄.     

Growth and spectroscopy of Dy doped in ZnWO4 crystal

Single-crystal ZnWO₄:Dy³⁺ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω₂, Ω₄, Ω₆ are obtained to be 7.76 × 10⁻²⁰ cm², 0.57 × 10⁻²⁰ cm², 0.31 × 10⁻²⁰ cm², respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO₄:Dy³⁺ crystals are presented. Fluorescence lifetime of ⁴F_9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition ⁴F_9/2 → ⁶H_13/2 is potentially for application of yellow lasers.     

Enhancement of red emission assigned to inversion defects in ZnAl2O4:Cr3+ hollow spheres

ZnAl₂O₄:Cr³⁺ hollow spheres composed of secondary nanoparticles with single spinel phase were fabricated using carbon templets. Monitoring the emission of 687 nm, two wide excitation bands attributed to the electrons of Cr³⁺ transiting from ⁴A_2g (⁴F) → ⁴T_1g (⁴F) and ⁴A_2g (⁴F) → ⁴T_2g (⁴F) were observed. The broad excitation band at about 397 nm was asymmetric and consisted of two peaks, indicating that there was a trigonal distortion existing in the lattices. The intensity of all emitting peaks revealed sharp increasing trend with the sintering temperature increase, and the intensity of emission at 698 nm assigned to inversion defects was more intense than that of emission at 687 nm assigned to octahedral Cr³⁺ ions in the undistorted spinel lattice. The samples with higher synthesized temperature revealed longer decay time, and the relative weightage of shorter decay time component decreased with the increase of sintering temperature, indicating that the surface defects decreased.     

Electrical properties of reactively sputtered carbon nitride films

Carbon nitride films with β-C₃N₄ crystals of 200 nm grain size were grown on Si (1 0 0) substrates using magnetron sputtering. These films were characterized by transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Carbon nitride films had low surface roughness. Maximum N/C ratio of 0.5 was achieved in the films. Chemical bonds of sp, sp² and sp³ coexisted in the films. The fraction of each bond was related to the deposition conditions. The resistivities of the films were measured, which ranged from 1×10³ to 1×10⁷ Ω cm. The measured resistivity results indicated that the carbon nitride films had semiconductive properties. The resistivity largely depended on the sp³/sp² ratio. Effects of N₂ fraction, target current and substrate bias were investigated. All these deposition parameters had influence on the chemical bonds of the films, and on the resistivities too. High sp³/sp² ratio resulted in high resistivity.     

Color centers and charge state recharge in γ-irradiated Yb:YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe²⁺, Fe³⁺ and Yb³⁺ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe³⁺ and Fe²⁺ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb³⁺ → Yb²⁺ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe²⁺ → Fe³⁺ and Yb²⁺ → Yb³⁺ take place and the color centers responsible for the 385 nm band was destroyed.     

Energy transfer luminescence in (Eu,Nd) : tellurite glass

Here, we bring out an infrared transmitting new optical glass based on TeO₂ added with AlF₃ and LiF, containing dual rare earth ions (Eu³⁺,Nd³⁺) as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu³⁺ (⁵D₀ → ⁷F₂ at 615 nm) as a function of temperature both in the presence and absence of Nd³⁺ ions. The energy transfer rates (W_tr), critical distances (R₀) and transfer efficiencies (η_tr) have been evaluated based on the measured lifetime data of this glass.     

Ni2+掺杂尖晶石相透明微晶玻璃制备及光学性能

实验制备了Ni²⁺掺杂的ZnO-MgO-Al₂O₃-SiO₂(ZMAS)体系的透明微晶玻璃, 研究了微晶玻璃的超宽带发光现象。热分析结果表明样品的玻璃化转变温度(T_g)和析晶峰温度(T_c)分别为754℃和948℃。采用X射线粉末衍射分析了两种热处理制度对玻璃的晶体形核、晶体生长及物相变化的影响, 结果表明: 采用阶梯温度热处理制度可以得到Ni²⁺掺杂的尖晶石相透明微晶玻璃。紫外-可见吸收光谱和荧光光谱测试表明制备的Ni²⁺掺杂ZMAS微晶玻璃中Ni²⁺以四配位和六配位共同存在于尖晶石相中, 红外荧光中心位于1324 nm的样品荧光半高宽达490 nm。样品的超宽带荧光主要是由于微晶玻璃中六配位Ni²⁺在ZnAl₂O₄和MgAl₂O₄形成的尖晶石相固溶体晶体场中的³T_2g(³F)→³A_2g(³F) 能级跃迁。实验结果表明, 制备的微晶玻璃在超宽带光纤放大器等光子器件中具有潜在的应用前景。     

Optical properties, fluorescence mechanisms and energy transfer in Tm, Ho and Tm -Ho doped near-infrared laser glasses, sensitized by Yb

The optical properties of the rare elements Tm³⁺, Ho³⁺ and Yb³⁺ were systematically investigated in various glasses. The Tm³⁺ doped aluminozircofluoride glass shows higher quantum efficiency, longer lifetime and stronger fluorescence intensity than Tm³⁺ doped YSGG crystal and other Tm³⁺ doped glasses for the ³H₄ → ³H₆ transition. Similar quantum efficiency, longer lifetime and stronger fluorescence intensity were also found in Ho³⁺ doped aluminozircofluoride glass for the ⁵I₇ → ⁵I₈ transition. The higher quantum efficiencies of Tm³⁺ and Ho³⁺ in aluminozircofluoride glass are due to the longer lifetime and the lower phonon energy. The fluorescence mechanisms and energy transfer in the Yb³⁺ -Tm³⁺ system, Yb³⁺ -Ho³⁺ system and Yb³⁺ - Tm³⁺ -Ho³⁺ system were studied. The very strong fluorescence intensities in the Yb³⁺ -Tm³⁺ system for Tm³⁺ and the Yb³⁺ -Tm³⁺ -Ho³⁺ system for Ho³⁺ which are 1.68 times that of Tm³⁺ doped YSGG crystal and 2.25 times that of Tm³⁺---Ho³⁺ codoped YSGG crystal are attributed to the efficient Yb³⁺ → Tm³⁺, Yb³⁺ → Ho³⁺ and Tm³⁺ → Ho³⁺ energy transfer processes. The fluorescence processes are described by cross relaxations of ²F_5/2 → ³H₅ → ³H₄ → ³H₆ → ²F_7/2 and²F_5/2 → ³H₅ (or ²F_5/2 → ⁵I₆ → ³H₅) → ³H₄ → ⁵I₇ → ⁵I₈ → ³H₆ → ²F_7/2.     

In situ co-precipitation synthesis and photoluminescence of YxGd1−xVO4:Tm microcrystalline phosphors by hybrid precursors

Y_xGd_1−xVO₄:Tm³⁺ (5 mol%) phosphors were prepared by in situ co-precipitation technology with the different content ratio of Y/Gd (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, respectively). During the process, rare earth coordination polymers with o-hydroxylbenzoate were used as precursors, composing with polyethylene glycol (PEG) as dispersing media. After heat-treatment of the resulting multicomponent hybrid precursors at 900 °C, the samples were obtained. SEM indicated the particles present good crystalline state, whose crystalline grain sizes were about 0.2–2 μm. Under the excitation of 257 nm, all the materials show the characteristic emission of Tm³⁺ which is the strong blue emission centered at 475 nm originating from ¹G₄ → ³H₆ of Tm³⁺. Besides this, concentration quenching appears in the system of YVO₄:Tm³⁺ and GdVO₄:Tm³⁺. And when x reaches 0.5, the system of Y_xGd_1−xVO₄:Tm³⁺ shows the strongest blue emission.     

Crystal growth and spectral properties of pure and Co-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

A method for determining the branching ratio for the superallowed decay: C(0, gs) → B(0, 1.74 MeV) + e + ν

We describe a new way of determining the strength of the superallowed branch of the β-decay of ¹⁰C, ¹⁰C(0⁺, gs) → ¹⁰B(0⁺, 1.74 MeV) + e⁺ + ν. Precise knowledge of the branching ratio is needed to compute the experimental ft-value and the weak vector coupling constant.     

Two- and three-photon upconversion of LaOBr:Er

In this work, the LaOBr:Er³⁺ (0.1%) powders were prepared by solid state reaction. The structural properties of LaOBr:Er³⁺ were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The results show that LaOBr:Er³⁺ has low phonon energy, which indicate that LaOBr:Er³⁺ may have high luminescent efficiency. Under excitation into ⁴I_11/2 level of Er³⁺ ions by 980 nm laser, the two- and three-photon upconverted luminescence of LaOBr:Er³⁺ were recorded. The most intense emissions were come from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions. The upconversion mechanisms were studied in detail through laser power dependence, and results show that excited state absorption is responsible for the upconversion. The upconversion properties indicate that LaOBr:Er³⁺ may be used in upconversion phosphors.