Radiation induced colour centers and damage in YAlO 3 :Ce and YAlO 3 :Ce,Zr scintillators

Radiation induced absorption spectra (irradiation up to 500 v Gy by 60 Co) and TSL of a set of YAP:Ce crystals co-doped by Zr 4+ were investigated. Positive effect of Zr 4+ co-doping was found, namely reduction of both the defect creation and presence of TSL active traps. Up to three absorption bands were observed in the radiation induced absorption spectra. They probably have different origin - from colour centers in the green part of the spectra to change of the Ce 3+ valency in the near UV.     

Pressure effects on bacteriophage T4

Abstract

The conformational changes which occur in bacteriophage T4 during infection can be simulated by hydrostatic pressure. The kinetics of the pressure induced process is measured by the decrease of the virus infectivity. Experimental results are explained by assuming that the virus population is composed of three parts which differ in their pressure sensitivity. It is shown that the phages which are the highly sensitive part lose this feature when they are alawly accustomed to pressure.     

Exafs studies of LiYF 4 -LiREF 4 solid solutions

In this work we are investigating dopant environments in LiYF 4 -LiREF 4 (RE=rare-earth cations) solid solutions, via EXAFS. The main aims are to identify the local environmental symmetry and the average lattice distortion as a function of the concentration and the type of the RE ion. LiY 1 m x RE x F 4 (RE=Gd or Lu) (0< x <1) single crystals were grown by the Czochralski technique under argon or CF 4 atmosphere, crystal-pulling rates were 0.6-1 v mm/h for <100>-oriented boules, with 8-25 v rpm rotation rates. Most of the crystals were also codoped with 2.7 v mol% of neodymium in the melt. EXAFS measurements were performed in transmission and fluorescence modes in the synchrotron XAS line of the LNLS, Campinas, Brazil, in and above the L III absorption edges of the RE ions. The samples were prepared as powder films, for the transmission mode measurements, and as powder or single crystals for fluorescence mode measurements. The WINXAS program was used for data reduction and fitting, and the FEFF6 package was used for the simulations of the spectra. The EXAFS oscillation curves were obtained by standard procedure.     

Quenching of Pyrene Fluorescence by Calix[4]arene and Calix[4]resorcinarenes

Interactions involving calixarene and its derivatives are of major importance due to their widespread applications as unique hosts. Fluorescence from a common probe pyrene is used to study interactions involving calix[4]resorcinarene [1a] and its tetra-morpholine derivative [1b] in 1 M aqueous NaOH. These compounds efficiently quench the pyrene fluorescence. A comparison with the fluorescence quenching behavior of N-methylmorpholine clearly indicates the presence of long-range interactions involving 1a and 1b; the interactions are specific to the calixarene molecular framework. This is not the case for a tetra-nitro-substituted calix[4]arene [2b], an electron/charge acceptor quencher, as p-nitrophenol also shows similar interactions with pyrene. Effectiveness of cesium as the quencher of pyrene fluorescence is reduced in the presence of electron/charge donating 1b; fluorescence enhancement is observed upon addition of cesium as the concentration of 1b is increased in the solution. The role of calixarene framework in interactions involving such compounds is established.     

CD Spectroscopic Study of Absolute Conformation and Configuration of Some 4-Hydroxychromans

CD data of the optically active 4-hydroxy (1–5) and 4-acetoxy chromans (6–8) were analyzed by two different approaches. The Snatzke-Antus treatment of chiraly perturbed chromane chromophore revealed M absolute conformation and 4S absolute configuration of the alcohols, i.e. P absolute conformation and 4R absolute configuration of the acetates. The proposed absolute configuration of the optically active alcohols was confirmed for 1 and 2 by the chiral excitone coupling method applied on their benzoates 9 and 10.     

Luminescence in BaSO4:Eu

Abstract

Photoluminescence and thermoluminescence in BaSO₄:Eu is reported. In earlier works, divalent Eu has been studied in BaSO₄. In the present work Eu was incorporated as in predominantly Eu³⁺ or Eu²⁺ form. It is shown that RE³⁺ ? RE²⁺ conversion or RE²⁺ ? RE⁺ conversion is not an integral part of gamma induced TL. Eu³⁺ ? Eu²⁺ conversion, on the other hand, may be important in UV induced TL. Low UV efficiency of this material is attributed to poor Eu³⁺ ? Eu²⁺ conversion. This is in quite contrast to the analogus material CaSO₄: Eu.     

Optical properties and laser potential of dysprosium doped YAl 3 (BO 3 ) 4 (YAB) crystal

The absorption and emission spectra were measured at 5 and 300 v K. The positions of the selected Dy 3+ levels and their Stark components, determined from optical spectra at 5K, are presented. In this work an attempt is made to assess the potential of dysprosium doped YAl 3 (BO 3 ) 4 crystal as a laser active material operating near 570 v nm. The emission cross-section of a potential laser line at 570 v nm connected with 4 F 9/2 M 6 H 13/2 transition was estimated.     

Biological effects induced by swift heavy ions of lithium on aqueous solution of plasmid pMTa4

Biological samples exposed to swift heavy ions sustain damage on different components. Damage to DNA, a critical component of a living system, has considerable biological implications. In this study aqueous solution of plasmid pMTa4 was exposed to varying fluence of swift ⁷Li ions and its different topological forms were analysed by agarose gel electrophoresis to study the induced damage. To monitor radiation labile nucleotide sequence the ⁷Li ions exposed plasmid was degraded by three different restriction endonucleases and also analysed by agarose gel electrophoresis. The results show that ⁷Li ions predominantly induced double strand breaks in the plasmid DNA in a dose-dependent manner and affected preferentially the GC-rich motifs of the DNA. The results suggest that ⁷Li ions induce premutagenic lesions at an enhanced frequency in segments of the DNA which are rich in CG content as compared to GC-poor segments.     

An efficient synthesis of substituted 2-iminothiazolidin-4-one and thiadiazoloquinazolinone derivatives

A convenient synthesis of functionalized 2-iminothiazolidin-4-ones and thiadiazoloquinazolinones has been achieved by the reaction of dialkyl acetylenedicarboxylates (DAAD) with 1-pheny-3-pyridin-2-yl-thiourea (1) and 3-amino-2-mercapto-3H-quinazolin-4-one (8), respectively. The starting materials for these processes were prepared from phenyl isothiocyanate, 2-aminopyridine for (1) and anthranilic acid, carbon disulfide, hydrazine for (8). Treatment of these compounds with DAAD resulted in the formation of an intermediate that readily underwent intramolecular cyclization to afford functionalized five membered heterocyclic rings was formed.     

Spectrophotometric Characteristics of New Pyridylindolizine Derivatives Solutions

Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence.     

Transport and magnetic properties of the compounds YbNi4In and YbNiIn4 with valence-unstable Yb

The electrical resistance, thermal emf, and magnetic susceptibility of the compounds YbNi₄In and YbNiIn₄, with valence-unstable Yb, are measured at temperatures of 4.2–300 K. The valence state of Yb is identified by measuring the x-ray L _III absorption spectra at T=300 K. YbNi₄In is shown to have a Kondo magnetic lattice and exhibit crystal-field effects. The preferred scheme is splitting of the 4f level of Yb³⁺ with doublet formation in the ground and first excited states. In the case of YbNiIn₄, a valence-unstable state of Yb is formed that makes no significant additional contributions to the transport coefficients. Fiz. Tverd. Tela (St. Petersburg) 41, 1918–1921 (November 1999)     

Pressure and temperature-dependent raman study of ZnWO4

Abstract

The Raman spectra of monoclinic ZnWO₄ (c⁴ _2h-space group) are reported over wide ranges of pressure (0-24GPa) and temperature (13-970 K). All 18 Raman active pho-nons are observed throughout these ranges. Combining the pressure and temperature Raman data, an identification scheme is suggested which makes possible to distinguish the internal modes (vibrations in the octahedral WO₆ units) from the external ones (pure lattice modes). All phonons harden with pressure, thus showing normal positive dω/dP slopes, and soften with temperature in the region 250 - 970 K (normal negative dω/dT slopes). However, two phonons show a change of slope sign below 300 K, resulting in small positive slopes at low temperatures. Since the pressure dependence of these two phonons is normal and linear, it is concluded that their anomalous, non-linear dependence with temperature is due to anharmonic (temperature induced) phonon interactions rather that volume expansion. It is found that ZnWO₄ remains stable throughout the pressure and temperature ranges.     

Martensitic transformation and soft modes in KAlF4

Abstract

The structural phase transition observed at ?13°C in KAlF₄ is shown to be martensitic. The results of an investigation of the phonon spectrum by inelastic neutron scattering are reported. It is shown that the transition is preceded by the softening of a flat phonon branch. A model is proposed to explain how such a softening is related to the martensitic transition.     

Time-Resolved Spectroscopy in ZnWo4 and ZnWO4:Fe

Time-resolved luminescence and absorption of ZnWO⁴ and ZnWO₄:Fe have been studied. The fast decaying luminescence at ～1.7eV is attributed to either Fe^2? or a Fe^3? related center. The two observed stages in luminescence decay kinetics under ionising radiation are suggested to be due to two types of self-trapped excitons.     

Photoinduced color centers creation in superionic crystals RbAg 4 I 5

Abstract

A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionic RbAg ₄ I ₅ crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystals RbAg ₄ I ₅ due to additive coloring in iodine vapours, ionic implantation and γ-ray irradiation are considered.     

The infrared absorption of OH in ZnWO4 and ZnWO4: Fe single crystals

OH^--ions play an important role in the charge compensation of defects in ZnWO₄. The interstitial OH in ZnWO₄: Fe affects the optical properties, resulting in a sharp symmetric absorption peak at 3445 cm^-1 (RT). The substitutional OH in pure ZnWO₄ produces a broad absorption band at 3420 cm^-1 (RT). The characteristics of both bands are studied at low temperature and in polarized light respectively. The effects induced by the isotopic substitution of H with D are also considered.     

Growth and spectroscopic characteristics of Nd-doped PbWO4 crystal

Nd-doped PbWO4 crystals are grown by using the modified Bridgman method.The spectroscopic properties of the crystals are investigated.The changes of the absorption band at 350 nm are discussed for samples annealed at 740℃ and 1040℃.The radiative lifetime of the 4 F 3/2 level is calculated by using the Judd-Ofelt theory according to the absorption spectrum of 0.5 at.% Nd-doped PbWO 4 crystal.The spontaneous Raman scattering properties of the crystals are analysed.     

Multi-quantum photoconductivity in Cdln2S4

A study has been made of photoconductivity in Cdln₂S₄ induced by 1.17 eV photons from a Q-switched neodymium laser. Both three-photon absorption, and two-photon absorption involving the emission of a phonon, have been investigated. The experimental data are in satisfactory agreement with the theory of multi-quantum transitions which takes into account the peculiarities of crystal zone structure.The investigation of competing multi-quantum transitions is a new method which permits one to obtain information on the fundamental optical constants of solids.     

Size‐Dependent Synthesis of Cu12Sb4S13 Nanocrystals with Bandgap Tunability

Copper antimony sulfide (CAS) is an attractive material with a suitable bandgap for sunlight absorption and a high absorption coefficient in solar cells. There are few works focused on the size‐controllable synthesis of CAS nanocrystals, and no work reports on the special character of bandgap tunability until now. Herein, high‐quality monodispersed tetrahedrite (Cu₁₂Sb₄S₁₃) nanocrystals are synthesized through a novel solution‐based method by using thiols as ligands. The as‐prepared Cu₁₂Sb₄S₁₃ nanocrystals have a narrow size distribution and wide size range from 2 to 16 nm, while their absorption band edges are continuously tunable from 620 to 780 nm. The quantum size effects with bandgap tunability of Cu₁₂Sb₄S₁₃ nanocrystals are observed for the first time.     

Effects induced by 𝛄-irradiation on intraband transitions in Sr2+-doped ammonium zinc chloride crystals

Considerable changes were observed in the X-ray diffraction pattern of ammonium zinc chloride after doping with Sr²⁺ in different concentrations and after irradiating with γ rays at different doses. The effect of γ-radiation and Sr²⁺ content on optical parameters of (NH₄)₂ZnCl₄: x Sr²⁺ single crystals (x?=?0.00, 0.020, 0.039, 0.087 or 0.144?wt.%) has been investigated. The transmittance near the absorption edge of unirradiated crystals and crystals irradiated with different γ-doses has been measured, hence the absorption coefficient (α) was calculated. The values of α at room temperature increased under the influence of γ-irradiation. The rate by which α increases with photon energy just before the absorption edge is strongly inhibited by higher γ-doses. The type of intraband transition in (NH₄)₂ZnCl₄: x Sr²⁺ single crystals was found to be of the allowed indirect transition, and γ-irradiation had no effect on the type of transition. The values of the optical energy gap (E _g ) were calculated as a function of γ-dose. The effect of γ-irradiation was found to be more pronounced on samples doped with x?=?0.087 or 0.144?wt.% Sr²⁺. The results can be discussed on the basis of γ-irradiation-induced defects and Sr²⁺ concentration. A diagram representing probable transitions to the created bands due to irradiation could be constructed.