Inter- and intraconfigurational luminescence of Er 3+ ions in BaY 2 F 8 under VUV excitation

Using energy- and time-resolved spectroscopy the luminescence properties of Er 3+ doped BaY 2 F 8 crystals were investigated at 10 v K under VUV synchrotron radiation excitation. Radiative intraconfigurational f - f and interconfigurational d - f transitions in Er 3+ ions were observed under f - d excitation. Whereas the onset of 4 S 3/2 population via f - d excitation starts at 59 900 v cm m 1 , efficient excitation of emissions arising from the 2 P 3/2 state begins only above 67 000 v cm m 1 in VUV region. Such behaviour can be explained by a cross-relaxation process of the type ( 2 F(2) 5/2 , 4 I 15/2 ) M ( 2 P 3/2 , 2 P 3/2 ) taking place within f -states of Er 3+ ions finally populating the emitting 2 P 3/2 state.     

Defect states in Lu 3 Al 5 O 12 :Ce crystals

Wavelength-resolved TSL measurements after x-ray irradiation at room temperature were performed on undoped, Ce- and (Ce, Zr)-doped Lu 3 Al 5 O 12 crystals. Several glow peaks were observed in the 20-450 v C temperature region, whose intensities and emission spectra are influenced by doping. Namely, the TSL spectra are governed by defect and trace impurity-related emissions in the undoped crystal, while only the Ce 3+ emission is detected in the doped crystals. Moreover, EPR measurements performed at 12 v K revealed typical spectra of Ce 3+ (4f 1 , S =1/2) occupying Lu 3+ substitutional positions. In situ light irradiation (250-330 v nm) of the crystals results in a step-like decrease of the Ce 3+ EPR intensity. Such a behaviour can reflect a creation of Ce 4+ ions under UV irradiation or an increase of the Ce 3+ population in the excited (5d) state.     

Creation of electronic excitations and defects by vuv radiation (6-40 eV) in wide-gap solids

The processes of multiplication of electronic excitations (MEE), connected with the creation of secondary excitons or electron-hole (e-h) pairs by hot conduction electrons, are realized in wide-gap metal halides and oxides. In oxides, secondary e-h pairs can be also formed by 27-40 v eV photons due to L 1 VV Auger transitions (with the participation of 2s oxygen holes). The excitation spectra of luminescence and the creation spectra of electron F centres or hole V centres have been measured for Na 6 Al 6 Si 6 O 24 (NaI) 2x sodalites and MgO:Be, respectively, at 8-80 v K. A high local density of excitations has been revealed under MEE conditions in KBr and Br sodalites with self-trapping excitons and holes.     

MMgF4:Eu(M=Ca,Sr,Ba)体系中铕离子的发光中心及价态

合成了铕离子激活的MMgF4.磷光体,研究了Eu3+离子的光谱特征与基质化合物的关系,存在三类发光中心,讨论了基质组成对铕离子价态的影响.     

Congruent Sr 0.61 Ba 0.39 Nb 2 O 6 doubly doped with Ce and Cr: PHoto- and thermoluminescence investigations

Congruent Sr x Ba 1 m x Nb 2 O 6 (SBN, x=0.61) doped with Ce or Cr ions exhibits enhanced photorefractive properties and new spectral features like increased red sensitivity. Here special emphasis is placed on the luminescence features of doubly doped Ce+Cr SBN crystals. The luminescence excitation and emission spectra combined with the absorption of the impurities allow to draw conclusions about the origin of the charge carriers und their recombination. The well separated thermo-luminescence peaks detected and their spectral line shape in emission point to specific recombination processes following the thermal liberation of light-induced electron trapping centers: Nb 4+ polarons and VIS-centers created at low temperature under light irradiation. The thermal activation energy for the hopping motion of Nb 4+ polarons and of VIS-centers are estimated to be 0.18 - 0.02 v eV and 0.30 - 0.05 v eV respectively. Possible excitation and recombination mechanisms in SBN:Ce+Cr are discussed.     

Investigation of the superionic behaviour of BaF 2 ( x mol% LaF 3 ) by raman and brillouin scattering and molecular dynamics simulations

High temperature Raman and Brillouin light scattering experiments have been combined with molecular dynamics simulations to provide a comprehensive study of the superionic state of BaF 2 ( x v mol% LaF 3 ) over a particularly wide range of LaF 3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show the usual T 2g symmetry mode at 241 v cm m 1 , but for samples with x =20, 30 and 50 the dominant Raman mode is at higher frequencies and of E g symmetry. The temperature dependence of the Raman line-widths show initial near linear increases followed by substantial increases above temperatures ( T c ) at 1200, 850, 800, 975, 950 and 920 v K for x =0, 5, 10, 20, 30 and 50. In the Brillouin scattering experiments, the acoustic modes respectively related to elastic constants C 11 and C 44 initially showed a quasi-linear decrease in frequency with increasing temperature. Above the same characteristic values of T c , where the Raman line-widths show marked increases, there are substantial decreases in the elastic constant C 11 for all samples with x =0 to 50. Only the doped samples showed significant decreases in C 44 at corresponding values of T c . Molecular dynamics (MD) simulations have been carried out on the same systems. From the calculated mean square displacements, the diffusion coefficients ( D ) of the mobile fluorine ions were calculated as a function of temperature for each of the samples. Substantial increases in the values of D occur above the respective values of T c determined in the light scattering experiments. The MD simulations also provide details of the mechanisms of diffusion of the mobile fluorine ions. The results emphasize the role of motional effects as an explanation of the mechanisms responsible and provide a self-consistent explanation of the dominant processes in the superionic phase of doped fluorites.     

Analyticity of the density of states in the anderson model on the Bethe lattice

Let H=1/2+V on l²(B), whereB is the Bethe lattice andV(x),x B, are i.i.d.r.v.'s with common probability distribution. It is shown that for distributions sufficiently close to the Cauchy distribution, the density of states(E) is analytic in a strip about the real axis.     

The study of damage and optical properties in LiNbO3 implanted by MeV Er and He ions

Abstract

Two LiNbO₃ (X and Y cut) crystals from different companies were implanted by 3.0 MeV Er ions to a dose of 7.5 × 10¹⁴ ions/cm² and 3.5 × 10¹⁴ ions/cm² with different beam current densities, respectively. After annealing at 1060°C in air for 2 hours, one LiNbO₃ sample was implanted by 1.5 MeV He ions to a dose of 1.5 × 10¹⁶ ions/cm². The Rutherford backscattering/channeling and prism coupling method have been used to study the damage and optical properties in implanted LiNbO₃. The results show: (1) the damage in LiNbO₃ created by 3.0 MeV Er ions depends strongly on the beam current density; (2) after annealing at 1060°C in air for 2 hours, a good Er doped LiNbO₃ crystal was obtained; (3) there is waveguide formation possible in this Er-doped annealed LiNbO₃ after 1.5 MeV He ion implantation. It is suggested that annealing is needed to remove the damage created by MeV Er ions before the MeV He ion implantation takes place, to realize the waveguide laser for Er doped LiNbO₃.     

Radiation damage produced in quartz by energetic ions

Abstract

Present work deals with atomic and electronic alterations of the quartz structure by high energy ion irradiation. The atomic structure of irradiated quartz is probed by means of X-ray absorption spectroscopies (XANES, EXAFS). Electronic structure modifications are investigated by XPS and bulk paramagnetic point defects by ESR. The experimental data suggest that for light ions (O), irradiated quartz targets preserve their long range order. E' point defects, i.e. oxygen vacancy defects, are created along the ion path with a poor efficiency (2 GeV/E'), close to the efficiency of y rays. For heavier ions (Kr, Pb), irradiation damage consists of a trail of extended defects. These extended defects are composed of an amorphous SiO₂ state. The density of these amorphized regions is about 4% larger than the common relaxed silica. This poorly densified silica appears similar to that obtained by neutron irradiation of quartz. E’ defects are mostly located inside these amorphous zones (>85%).     

The colouration of CaF 2 crystals by keV AND GeV ions

CaF 2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 v nm. This includes the vacuum UV region. For 100 v keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10 17 v ions v cm 2 ) but no colour centres (F, F 2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10 12 v ions v cm m 2 attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 v nm in the VUV and bands at 604 v nm and 672 v nm in the visible region.     

Neutron-induced defects in the lithium tetraborate single crystals

The X-band ( x ; 9.4 v GHz) electron spin resonance (ESR) spectra of the un-doped isotopically enriched lithium tetraborate (LTB) Li 2 B 4 O 7 single crystals, irradiated by thermal neutrons (fluences | n =2.74 ‐ 10 15 1 1.79 v ‐ 10 18 v cm m 2 ) were investigated at 300 and 77 v K. The LTB crystals of high chemical purity and optical quality with different isotope compositions ( 6 Li 2 10 B 4 O 7 , 6 Li 2 11 B 4 O 7 , 7 Li 2 10 B 4 O 7 and 7 Li 2 11 B 4 O 7 ) were grown by Czochralski technique. The thermal neutrons (the total quantity >90%) with fluence near 10 18 v cm m 2 induce at least 4 different types of stable paramagnetic centers in the Li and B isotopically enriched LTB crystals. The ESR spectra, electron structure and efficiency of generation for centers, induced by thermal neutrons, essentially depend on neutron fluence and isotope composition of the LTB crystals. The local symmetry and the spin Hamiltonian parameters of the observed paramagnetic centers were determined and their electron structure were established. The possible models and formation mechanism of the radiation defects, induced by thermal neutrons in the LTB lattice, are proposed.     

An upper bound on the free energy for classical systems with Coulomb interactions in a varying external field

The thermodynamic limit is taken using a sequence of regions all the same shape as a given region of volume ||, with a specified distribution of normal field component on . We show that with magnetostatic interactions the limiting free energy density is bounded above by jhen where (,B) is the free energy density for a system of density in a uniform external fieldB and the inf is taken over all divergence-free fieldsB with given normal component on and all densities (x) compatible with particle number constraints of the form where _i is a sub-region of . A physical argument suggests that this upper bound is the true thermodynamic limit, and that it takes account demagnetization effects. Electrostatic interactions can be treated similarly.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Development of X-ray storage phosphor glass-ceramics

Europium- and bromine-doped fluorozirconate glass-ceramics show a significant photostimulated luminescence (PSL) effect after X-irradiation at room temperature. The PSL is assigned to the 5 d -4 f emission of Eu 2+ ions incorporated in barium bromide crystallites which are formed in the glass matrix upon suitable thermal annealing. The BaBr 2 crystallites grows in both the hexagonal and orthorhombic phases. The PSL efficiency of the glass-ceramic containing predominantly the hexagonal phase is only about 0.0025% of the well-known crystalline storage phosphor BaFBr:Eu used as a standard, whereas the glass-ceramic containing the orthorhombic phase has a relative efficiency of a few percent. Using the same formulation for the fluorozirconate glass-ceramic, but replacing Na by Rb and Li, results in the formation of RbBa 2 Br 5 microcrystallites after suitable annealing. The relative PSL efficiency increases to about 10%. The structural changes in these two fluorozirconate glass-ceramics were monitored by X-ray diffraction, photoluminescence, and electron paramagnetic resonance.     

Spectroscopy in propyne and ethyl-Chloride by means a tunable CO2 RF laser

Some lines in 5 band of propyne (CH₃CCH) and many strongest lines in the 9 band of ethyl- Chloride (C₂H₅Cl³⁵ A-type) are measured and identified, giving a new set of spectroscopic constants. In particular the ethyl-Chloride set allows to assign all the FIR transitions reported in literature.     

A Family of Balance Relations for the Two-Dimensional Navier--Stokes Equations with Random Forcing

For the 2D Navier--Stokes equation perturbed by a random force of a suitable kind we show that, if g(F) is an arbitrary real continuous function with (at most) polynomial growth, then the stationary in time vorticity field (t,x) satisfies where M_1 is a number, independent of g, which measures the strength of the random forcing. Another way of stating this result is that, in the unique stationary measure of this system, the random variables g((t,x) and |(t,x)|² are uncorrelated for each t and each x.This revised version was published online in March 2005 with corrections to the page numbers.     

Phonon-assisted luminescence anomalies in Eu2+ doped Ca1-xSrxF2 mixed crystals

Abstract

With increasing X on Ca_1-xSr_xF₂ mixed crystals doped with Eu²⁺ (4f⁶5d) ions, the absorption peak shifted linearly to that of SrF₂:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF₂ in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength.     

Spectrophotometric Determination of Cobalt with Di-2-Pyridyl Ketone Benzoylhydrazone

Abstract

A method for the spectrophotometric determination of cobalt (II) by complexation with di-2-pyridyl ketone benzoylhydrazone (DPKBH) in 50% (v/v) ethanolic solution is described. Cobalt (II) forms a 1:2 complex with DPKBH. The complex has maximum absorbance at 370 nm. Beer's law is obeyed over the range 0.1 – 2.8 μg.ml^?1. The effect of pH, effect of excess reagent, stability of the complex and the tolerance limit of many metal ions have been reported. The method is applied to the determination of cobalt in different alloys containing other metals ions.     

Cavity swelling of RAFM steel under 792 MeV Ar-ions irradiation at 773 K

China reduced-activation ferritic/martensitic steel is irradiated at 773 K with 792 MeV Ar-ions to fluences of 2.3×10²⁰ and 4.6× 10²⁰ ions/m², respectively. The variation of the microstructures of the Reduced-activation ferritic/martensitic (RAFM) steel samples with the Ar-ion penetration depth is investigated using a transmission electron microscope (TEM). From analyses of the microstructure changes along with the Ar-ions penetrating depth, it is found that high-density cavities form in the peak damage region. The average size and the number density of the cavities depend strongly on the damage level and Ar-atom concentration. Swelling due to the formation of cavities increases significantly with an increased damage level, and the existence of deposited Ar-atoms also enhances the growth of the average size of the cavities. The effect of atom displacements and Ar-atoms on the swelling of the RAFM steel under high energy Ar-ion irradiation is discussed briefly.     

Optical activity and damage recovery of erbium implanted strontium titanate

Single crystalline SrTiO 3 samples were implanted with Er ions of 150 v keV at room temperature with fluences of 5 ‐ 10 14 and 5 ‐ 10 15 . Annealing treatments were carried out both in reducing and oxidising atmospheres to recover the implantation damage. Infrared 1.54 v m Er 3+ luminescence between the two lowest spin-orbit levels 4 I 13/2 M 4 I 15/2 as well as emission from higher excited states 4 S 3/2 M 4 I 15/2 , 4 F 9/2 M 4 I 15/2 and 4 S 3/2 M 4 I 13/2 were observed in the implanted samples with highest fluence, annealed either in air or in vacuum. Multiple site location of Er 3+ ion is discussed and compared with RBS/C and emission channelling results that indicate that Er goes to Sr and Ti sites.