Design and achieving mechanism of upconversion white emission based on Yb/Tm/Er tri-doped KY3F10 nanocrystals

KY₃F₁₀:Yb³⁺/Tm³⁺/Er³⁺ upconversion nanocrystals are synthesized via a simple hydrothermal procedure. The nanocrystals emit the near equal energy white light with high brightness and favorable color balance when excited using a 980 nm continuous wave diode laser. The research of upconversion mechanism indicates that in addition to the energy transfer processes from Yb³⁺ to Tm³⁺ and Er³⁺, respectively, there exists a new process ¹G₄ (Tm³⁺) + ⁴I_11/2 (Er³⁺) → ³H₄ (Tm³⁺) + ⁴S_3/2 (Er³⁺).     

Effect of Ce(Eu) codoping on the spectroscopic properties of Er in bismuth-germanate glass

In order to improve the transition rate from the ⁴I_11/2 level to the 1.53 μm fluorescence emitting ⁴I_13/2 level of Er³⁺, the Ce³⁺ and Eu³⁺ ions were respectively introduced into the Er³⁺ doped bismuth-germanate glass with a composition of Bi₂O₃–GeO₂–Ga₂O₃–Na₂O. The energy transfer mechanisms between Er³⁺ and the codopants were discussed based on their energy level diagrams. Though Ce³⁺ was less effective than Eu³⁺ on the decrease of the ⁴I_11/2 level lifetime, it hardly influenced the lifetime value of ⁴I_13/2 level. Both the ⁴I_11/2 and ⁴I_13/2 levels were depleted severely at the same time with the codoping of Eu³⁺. As a result, Er³⁺/Ce³⁺ codoping improved the 1.53 μm fluorescence emission intensity, while Er³⁺/Eu³⁺ codoping had a deleterious effect on it. The results indicate that the Er³⁺/Ce³⁺ is a preferable codoped scheme for bismuth-germanate glass with low phonon energy to obtain an efficient broadband EDFA pumped at 980 nm.     

Boson Inverse Operators and a New Family of Two-photon Annihilation Operators

Abstract

We introduce the inverse of the Hermitian operator (ââ ^?) and express the Boson inverse operators â ^?1 and â ^??1 in terms of the operators â, â ^? and (ââ ^?)^?1. We show that these Boson inverse operators may be realized by Susskind-Glogower phase operators. In this way, we find a new two-photon annihilation operator and denote it as â ²(ââ ^?)^?1. We show that the eigenstates of this operator have interesting non-classical properties. We find that the eigenstates of the operators (ââ ^?)^?1 â ², â(ââ ^?)^?1 â and â ²(ââ ^?)^?1 have many similar properties and thus they constitute a family of two-photon annihilation operators.     

A Fast Pulsed Source of Ballistic R− Rotons in Superfluid 4He

Superfluid ⁴ He is unique in having well-defined excitations (R ^– rotons) with momentum oppositely directed to their velocity. If a beam of R ^– rotons can be produced, it could be unambiguously detected by quantum evaporation because the atoms will emerge in the opposite quadrant to that for atoms evaporated by R ⁺ rotons and phonons. Previous work shows that a heated metal film which is immersed in superfluid ⁴ He only creates phonons and R ⁺ rotons. A sponge-like heater does appear to produce R ^– rotons but, because it has a long time constant, it cannot be used in time of flight studies. We have developed a source that produces fast pulses of R ^– rotons suitable for time of flight measurements. The method uses interactions between R ⁺ rotons to create R ^– rotons, so a transient high density of R ⁺ rotons in a small confined volume is needed. The source appears to operate as we expect from a model of the evolution of the R ⁺ and R ^– roton populations.     

Precision Measurement of the 2

Abstract

The 4f¹³ 6s^{2 2}F_7/2–4f¹⁴ 5d ²D_5/2 3·43 μm infrared transition in ¹⁷²Yb⁺ has been driven for the first time and measured to be 87 360 087(4) MHz. The frequency was determined by probing a cloud of ¹⁷²Yb⁺ ions held in a radiofrequency trap in the presence of helium buffer gas. The infrared radiation was generated by difference frequency mixing in LiNbO₃. The frequency measurement is part of a programme to locate the 4f¹⁴ 6s ²S_1/2–4f¹³ 6s^{2 2}F_7/2 467 nm ultra-narrow transition in laser-cooled Yb⁺.     

Molten salt synthesis,characterization, and luminescence of SrWO4, SrWO4:Tb3+ and SrWO4:Eu3+ powders

SrWO₄, SrWO₄:Tb³⁺, and SrWO₄:Eu³⁺ powders were synthesized by a method of molten salt. XRD patterns showed that the synthesized powders have a pure tetragonal scheelite structure without the presence of deleterious phases. Scanning electron microscopy images show that powders are in the range of 20–35 nm. The emission spectrum of SrWO₄ shows the emission peak in the blue spectral region. The excitation spectra of SrWO₄:Tb³⁺ and SrWO₄:Eu³⁺ show the energy transfer from WO₄ ^2? group to Tb³⁺ and Eu³⁺ ions with a high efficiency. The emission spectrum of SrWO₄:Tb³⁺ shows the green emission at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. The emission spectrum of SrWO₄:Eu³⁺ shows the red emission located at 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The asymmetry ratio of SrWO₄:Eu³⁺ is found to be 5.54, which indicates that the Eu³⁺ ions are located in a lower symmetric site.     

An algorithm for spectral factorization using random search techniques

An approximation method for the energy spectrum of a stationary stochastic dynamical system is presented, which allows approximate functional rational factorization.This paper is in three parts. The first deals with a theoretical problem of approximation in Hardy Spaces, whose main result is the following:Let S⁽ⁱⁿ⁾, S be positive functions belonging to L¹(R_gw), such that log S⁽ⁿ⁾ and log S belong to L¹(R_ω, dω/1 + ω²).Let h⁽ⁿ⁾, h be the outer functions of the Hardy Space H²(Π₊) such that S^(g) = |h⁽ⁿ⁾|² and S = |h|² on iR.If S⁽ⁿ⁾ n^→∝ S in L¹(R_ω), and log S⁽ⁿ⁾ n^→∝ log S in L¹(R_ω, dω/1 + ω²), then: h⁽ⁿ⁾ n^→∝ h in H²(Π₊).The second part describes an effective algorithm, using random search methods, and gives an almost sure convergence result for it.The third part treats numerically two examples, permitting comparison of this algorithm with others (whenever there are…): the first example is a problem of approximation for a nonrational process (turbulence) that was considered in Ref. 22: the second example is a problem of model reduction (automatic) considered in Ref. 4.     

The 4πβ − γ coincidence method for parent-daughter decay in non-equilibrium: The measurement of the disintegration rates of 47Ca-47Sc, 45Ca

A 4πβ ? γ coincidence technique, employing the “computer discrimination” method of data collection with a pressurized gas flow proportional counter in the β-channel, is used to determine the individual activities in a mixture of ⁴⁷Ca-⁴⁷Sc and ⁴⁵Ca, where the parent-daughter decay ⁴⁷Ca-⁴⁷Sc is not in equilibrium. Calibration figures for an NPL ionization chamber are derived for both ⁴⁷Ca and ⁴⁷Sc.The general case of a mixture of β^?-γ or β^?-emitting radionuclides is discussed and the difficulties which can result from the use of conventional methods of efficiency variation are outlined, and the advantage of using the computer discrimination method is pointed out, particularly when the shortest half-life is of the order of a day.     

NaScMo<Subscript>2</Subscript>O<Subscript>8</Subscript>:RE<Superscript>3+</Superscript> (RE = Tb,Eu, Tb/Eu,Yb/Er,Yb/Ho) phosphors: hydrothermal synthesis,energy transfer and multicolor tunable luminescence

NaScMo₂O₈:RE³⁺ (RE = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho) phosphors were successfully synthesized by surfactant-free hydrothermal method and post-calcination treatment. The energy transfer (ET) of MoO₄ ^2? → Tb³⁺ → Eu³⁺ was proved by photoluminescence spectra and decay features. Multicolor emissions (green → yellow → red) were obtained by adjusting the ratio of Tb³⁺/Eu³⁺ upon excitation into the MoO₄ ^2? at 292 nm. The ET of Tb³⁺ → Eu³⁺ was demonstrated to be a resonant type via a dipole–dipole mechanism, and the crystal distance (R _c) was calculated by the quenching concentration method. Under 980 nm excitation, the emission of NaScMo₂O₈:RE³⁺ (RE = Yb/Er, Yb/Ho) showed strong green (Yb³⁺/Er³⁺: ⁴S_3/2, ²H_11/2 → ⁴I_15/2; Yb³⁺/Ho³⁺: ⁵S₂ → ⁵I₈) luminescence, respectively. Moreover, the doping concentration of the Yb³⁺ has been optimized under a fixed concentration of Er³⁺ and Ho³⁺, respectively. The NaScMo₂O₈:RE³⁺ phosphors have potential applications for color displays and light-emitting devices due to a variety of luminous colors.     

Lead oxide hydroxide clusters in Pb9O(OH)4A,zeolite A exchanged with Pb2+ at Ph 6.0

The crystal structure of Pb₉O(OH)₄A, zeolite 4A exchanged with Pb²⁺ at pH 6.0 and evacuated at 26°C, has been determined by single-crystal X-ray crystallography. Two separate (Pb²⁺, OH⁻, O²⁻) clusters were found. In each sodalite unit, a (Pb²⁺)₃(O²⁻)(OH⁻)₃ cluster, a distorted Pb₄O₄ cube with one Pb²⁺ missing, coordinates via its oxygens to four Pb²⁺ ions at 6-ring sites to give [Pb₇O(OH)₃]⁹⁺. In half of the large cavities, a [Pb₂(OH)₂]²⁺ cluster may have formed. The remaining Pb²⁺ ion is near the center of an 8-ring. The oxygen positions are somewhat uncertain, and the presence of hydrogen atoms is inferred.     

A reciprocating liquid helium pump used for forced flow of supercritical helium

The performance of a small double acting piston pump for circulating helium in a closed heat transfer loop is described. The pump was manufactured by LINDE AG, Munich, West Germany. The measured flow rate of supercritical helium was about 17 gs^?1 (500 lhr^?1) with a differential pressure of Δρ = 0.5 × 10⁵Nm^?2 at a working pressure of p = 6 × 10⁵Nm^?2. At differential pressures beyond 0.5 × 10⁵Nm^?2 the volumetric efficiency decreases.     

Isolation of actinium-225 for medical purposes

A procedure is described for isolation and purification of ²²⁵Ac as a ²²⁹Th daughter decay product using ion exchange. The process includes the following steps: separation of ²²⁹Th from a mixture of ²²⁵Ac and ²²⁵Ra (²²⁵Ac precursor) using an anion-exchange resin; separation of ²²⁵Ac and ²²⁵Ra using a cation-exchange resin; purification of ²²⁵Ac to remove inactive impurity cations (primarily Fe) using an anion-exchange resin; final purification of the product on a column with a cation-exchange resin.     

16O contamination in 4He analysis beams

The ⁴He⁺ beam from a Van de Graaff accelerator is often accompanied by an ¹⁶O⁺ beam of the same energy. If, after acceleration and before magnetic analysis, one electron is stripped from the oxygen ion to form ¹⁶O²⁺, these ions will not be separated from ⁴He⁺ during magnetic analysis. The ¹⁶O²⁺ fraction in the ⁴He⁺ beam was measured by analyzing back-scattering spectra for a thin Au film and the O to He ion charge ratio of 2:1 was confirmed by electrostatic deflection. Ion source conditions and the pressure in the beam lines strongly affect the ¹⁶O²⁺ fraction and the dependence of the O²⁺/O⁺ ratio on pressure is found to be in approximate agreement with predicted values. A formula for estimating the ¹⁶O²⁺ beam intensity, based on charge exchange data and measurement of the primary ¹⁶O⁺ beam intensity, is N[O²⁺] = 13 P(torr) l(cm) N[O⁺], where P is the total gas pressure, l the length of the beam line between the accelerator and switching magnet and N[O²⁺] and N[O⁺] are the beam intensities of the respective species. The ¹⁶O²⁺ contamination of ⁴He⁺ beams is easily removed by electrostatic separation.     

Behavior of radioaerosols formed by evaporation of 137Cs131I and 137CsOH from the metal surface in an electrostatic field

The behavior of radioaerosols formed by condensation of supersaturated ¹³⁷Cs¹³¹I and/or ¹³⁷CsOH vapor in an electrostatic field was studied. Supersaturated ¹³⁷Cs¹³¹I and/or ¹³⁷CsOH vapor was generated by evaporation of salt crystals from a metal surface heated to high temperatures owing to ohmic resistance. By applying additional potential to the aerosol generator, it is possible to control the behavior of ¹³⁷Cs¹³¹I, ¹³⁷CsOH, or ¹³⁷Cs¹³¹I + ¹³⁷CsOH aerosols in an electrostatic field.     

Sorption of 60Co, 90Sr, 90Y, and 137Cs from aqueous solutions onto Mg-Ln layered double hydroxides (Ln = Ce, Pr, Sm, Gd)

Sorption of ⁶⁰Co, ⁹⁰Sr, ⁹⁰Y, and ¹³⁷Cs from aqueous solutions onto Mg-Ln layered double hydroxides (LDHs) (Ln = Ce, Pr, Sm, Gd) was studied. All the synthesized LDH-Mg-Ln-CO₃ samples (Ln = Ce, Pr, Sm, Gd) sorb ¹³⁷Cs poorly. At a contact time of the solid and liquid phases of 15 min and V/m = 50 mL g^?1, K _d of ¹³⁷Cs is no higher than 1.0 mL g^?1. Despite similar composition of the LDH-Mg-Ln-CO₃ samples (Ln = Ce, Pr, Sm, Gd), they noticeably differ in the ability to sorb ⁹⁰Sr. At a contact time of the solid and liquid phases of 15 min and V/m = 50 mL g^?1, Kd of ⁹⁰Sr varies from 10 to >5 × 10³ mL g^?1. All the synthesized LDHs efficiently sorb ⁹⁰Y and ⁶⁰Co. At a contact time of the solid and liquid phases of 15 min and V/m = 50 mL g^?1, K _d of ⁹⁰Y and ⁶⁰Co from aqueous solutions with LDH-Mg-Ln-CO₃ (Ln = Ce, Pr, Sm, Gd) exceeds 5 × 10³ mL g^?1.     

Photo-Induced Construction and Recovery of Cu+ Sites in Metal–Organic Frameworks

The adjustment of the valence state of metal ions is crucial for various applications because peculiar activity originates from metal ions with specific valence. Cu⁺ can interact with molecules possessing unsaturated bonds like CO via π-complexation, while Cu²⁺ doesn't have such ability. Meanwhile, Cu⁺ sites are easily oxidized to Cu²⁺, leading to the loss of activity. Despite great efforts, the development of a facile method to construct and recover Cu⁺ sites remains a pronounced challenge. Here, for the first time a facile photo-induced strategy is reported to fabricate Cu⁺ sites in metal–organic frameworks (MOFs) and recover Cu⁺ after oxidation. The Cu²⁺ precursor was loaded on NH₂-MIL-125, a typical visible-light responsive Ti-based MOF. Visible light irradiation triggers the formation of Ti³⁺ from Ti⁴⁺ in framework, which reduces the supported Cu²⁺ in the absence of any additional reducing agent, thus simplifying the process for Cu⁺ generation significantly. Due to π-complexation interaction, the presence of Cu⁺ results in remarkably enhanced CO capture capacity (1.16 mmol g⁻¹) compared to NH₂-MIL-125 (0.49 mmol g⁻¹). More importantly, Cu⁺ can be recovered conveniently via re-irradiation when it is oxidized to Cu²⁺, and the oxidation-recovery process is reversible.     

Ion probe technique for the study of gallium diffusion in silicon nitride films

The penetration of Ga in films of amorphous Si₃N₄ about 2000 Å thick on Si substrates has been studied. The films were produced by pyrolysis. Diffusion profiles were obtained by surface exposure to Ga vapor, and the implantation profiles by ion bombardment in an isotope separator. Evaluation of the profiles was effected by means of sputtering in a secondary ion microanalyzer. For depth calibration, ion yield profiles of ⁶⁹Ga⁺ of ⁷¹Ga⁺ were compared with the profiles of ³⁰Si⁺, ⁷⁰(Si₂N⁺, SiN⁺₃) and ⁷²Si₂O⁺. The integration of implantation peaks furnished a means of obtaining absolute values of Ga concentrations from the secondary ion intensities. Hence the surface concentration of vapor-deposited Ga at 1100°C was assessed to be of the order of 8 × 10²⁰ atoms cm^-3. The diffusion coefficient of Ga in Si₃N₄ at 1100°C was found to be about 5 × 10^-17 cm² s^-1. The method, which combines sputtering and mass spectrometry, appears to be applicable for measuring diffusion coefficients in this system down to about 3 × 10^-18 cm² s^-1.     

Enhanced G4 emission in NaLaF4: Pr, Yb and charge transfer in NaLaF4: Ce, Yb studied by fourier transform luminescence spectroscopy

A high resolution luminescence study of NaLaF₄: 1%Pr³⁺, 5%Yb³⁺ and NaLaF₄: 1%Ce³⁺, 5%Yb³⁺ in the UV to NIR spectral range using a InGaAs detector and a fourier transform interferometer is reported. Although the Pr³⁺(³P₀ → ¹G₄), Yb³⁺(²F_7/2 → ²F_5/2) energy transfer step takes place, significant Pr³⁺¹G₄ emission around 993, 1330 and 1850 nm is observed. No experimental proof for the second energy transfer step in the down-conversion process between Pr³⁺ and Yb³⁺ can be given. In the case of NaLaF₄: Ce³⁺, Yb³⁺ it is concluded that the observed Yb³⁺ emission upon Ce³⁺ 5d excitation is the result of a charge transfer process instead of down-conversion.     

Test beam results of Current Injected Detectors (CID) irradiated up to 5×10 1 MeV neq/cm

Two full size strip detectors were investigated in this study: one with p⁺ strips (p⁺/n⁻/n⁺) and another with n⁺ strips (n⁺/p⁻/p⁺). Both detectors, are made of magnetic Czochralski silicon (MCz-Si) and irradiated to S-LHC fluencies, were tested with 225 GeV muon beam in the CERN H2 area. The Current Injected Detector (CID) sensors were operated in a cooling box capable of providing a −53 °C temperature. Results indicate a relative charge collection efficiency (CCE) at 5×10¹⁵ n_eq/cm² above 30% in irradiated p⁺/n⁻/n⁺ CID detector at 600 V bias voltage. The signal to noise ratio of this CID module was about eight and a forward current of 30 μA was needed for detector biasing. In standard reverse bias, the same detector could not provide a sufficiently large signal for particle tracking purposes. A p-type (n⁺/p⁻/p⁺) sensor was irradiated to a fluence of 2×10¹⁵ n_eq/cm² and measured under the same test beam conditions. According to the theory of CIDs developed by the CERN RD39 Collaboration, this detector module could be biased up to only 230 V due to the low irradiation fluence. The CCE at 230 V was 35% in CID operation and 20% when reverse biased.     

Influence of repeller potential on ion-molecule reactions in methane and carbon tetrafluoride mixtures

Investigations of ion-molecule reactions were performed for methane-carbon tetrafluoride mixtures of different compositions. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment) and total mixture pressure was fixed at 13.3 Pa. Measurements were made using a quadrupole mass spectrometer with a high-pressure ion source. Primary ions CH₄⁺, F⁺, CF⁺ and CF₃⁺ were produced by electrons with energy of 300 eV. Secondary ions CH₅⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₂H₇⁺ and CF₃⁺ were observed as the result of ion-molecule reactions.The influence of repeller potential on ion-molecule reactions efficiency was examined.