Positron states and nanoobjects in proton-irradiated quartz single crystals: Positronium atom in quartz

The influence of proton bombardment and metal atom impurities on the structure of quartz single crystals has been studied. The related defects have been studied using positron annihilation spectroscopy (angular correlation of positron-annihilation photons), acoustic absorption, and optical absorption measurements. It is shown that the presence of a narrow component f in the angular distribution of annihilation photons (ADAP), which is related to the formation of parapositronium, determines a high sensitivity of this method with respect to features of the crystal structure of quartz. It is established that the defectness of the structure of irradiated quartz crystals can be characterized by the ratio f/f ₀ of the relative intensities of narrow components in the ADAP curves measured before (f ₀) and after (f) irradiation. Any process leading to a decrease in the probability of positronium formation (e.g., positron loss as a result of the trapping on defects and the interaction with impurity atoms and lattice distortions) decreases the intensity of the narrow component. Based on the ADAP data, estimates of the radii and concentrations of nanodefects in quartz have been obtained and their variation upon annealing at temperatures up to T = 873 K has been studied.     

Positron annihilation in Pb2+ doped KCl single crystals

The angular distribution of annihilation photons (ADAP) has been measured in a pure KCl single crystal and in one doped with Pb²⁺ impurities to concentrations of 100 ppm, 550 ppm and 1050 ppm. In unannealed, impurity doped, crystals the intensity of the narrow component increases with increase of impurity concentration. The narrowing of the ADAP curves is explained by assuming trapping of positrons at impurity induced positive ion vacancies. On annealing, the result on the 550 ppm impurity doped crystal shows that there is a dissolution of impurity-vacancy complexes at nominal concentrations of impurity, and the result on the 1050 ppm crystal shows that there is precipitation of impurity for very high concentrations.     

Radiation-induced nonlinear optical response of quartz fibers

The intensity of radiation-induced luminescence and transient optical losses in KU-1 (Russia) and K-3 (Japan) quartz glass optical tibers irradiated in a fast pulsed fission reactor (a pulse duration of 80 μs and a neutron flux up to 7 × 10¹⁶ cm^–2 s^–2) has been measured in the visible range. The intensity of the fast luminescence component nonlinearly depends on the neutron flux. The luminescence intensity and the transient optical losses depend on the probe light intensity. Suppression of radiation-induced luminescence is observed at wavelengths that are longer or shorter than the probe light wavelength. Light probing leads to an increase in transient optical losses and a more rapid recovery of transparency. A model of two photon fluxes is proposed to analyze the relationship of the effects of suppression of radiation-induced luminescence and the increase in optical losses upon light probing. The effect of suppression of radiation-induced luminescence can be used to control the optical properties of fibers in radiation fields.     

Positronium atom in solids

The angular distribution of annihilation 's in quartz shows that the half-width of the narrow component of the correlation curves depends on the state of aggregation (whether the substance is a single crystal, a powder, or a glass). Before annihilation, the positronium atoms may be captured by defects (vacancies, pores, or regions of reduced electron density); if this is true, the half-width of the narrow component and the long positron lifetime depend on the characteristics of the defects or traps. The sizes of the defects in certain solids (quartz glass; powdered beryllium, magnesium, and aluminum oxides; and polytetrafluoroethylene) are evaluated from the experimental half-width of the narrow component and the long positron lifetime.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 59–64, May, 1971.     

Radiation-induced E″ centers in crystalline SiO2

Electron spin resonance has been used to study three similar, but distinct, S = 1 defects (labelled E″ centers) in high-quality synthetic quartz crystals. These centers are produced by electron irradiation and their concentrations depend on the irradiation temperature, the nature of previous irradiations and thermal anneals, and whether the sample is swept or unswept. The radiation-induced mobility of interstitial alkali ions (Li⁺ and Na⁺) correlates with the production of E″ centers.     

Study of radiation-induced damage to type III–V semiconductor compounds irradiated with γ quanta and protons using positron annihilation spectroscopy

The effect of proton and ?? radiation on characteristics of the spectra for the angular distribution of annihilation photons (ADAP) have been studied in the case of positron annihilation in GaAs and GaP single crystals. Relative variations in defect accumulation and annealing under irradiation and subsequent isochronous annealing of the samples have been studied using variations in the basic parameters of the ADAP spectra. In both cases (GaAs and GaP), the variations in the ADAP spectral parameters as functions of the annealing temperature have a steplike character, which is interpreted as the formation of a certain type of defects with different annealing activation energies.     

The emission of photons and the dynamics of submicrodefects on the surface of noble metals

The shape and concentration of defects, as well as the intensity of electroluminescence from the back side of Cu, Ag, and Au samples with their front side irradiated by a laser shot, are studied experimentally. It is shown that there exists a correlation between the electroluminescence intensity and the concentration of radiation-induced defects, which is consistent with the dislocation model of luminescence.     

Electronic excitations and optical response of metal nanocomposites under heavy ion implantation

The optical transmission and ion-induced luminescence under implantation of copper ions into quartz glass (a-SiO₂) have been measured to study the processes of formation of copper nanoparticles. It is shown that in situ measurements are more informative in comparison with the ordinary approach—investigation of the properties of ion-implanted nanocomposites only after implantation. A series of experiments was performed to prove that the ion-induced luminescence band at 545–550 nm is due to Cu⁺ ions dissolved in a-SiO₂. The combined use of in situ optical techniques makes it possible to monitor the states of implanted copper (metal nanoparticles and dissolved atoms) by the change in the optical absorption near the surface plasmon resonance of nanoparticles and by the intensity of ion-induced luminescence of Cu⁺ states in solid solution. It is shown that the optical bands of defects, dissolved copper, and nanoparticles can be separated within a simple linear approximation. Near the surface plasmon resonance and defect bands, ion-induced transient optical absorption has been revealed. The transient optical absorption near the surface plasmon resonance is explained by the temperature effect. The relationship between the electronic excitation, radiation-induced optical response, and the kinetics of nanoparticle formation is analyzed. Several stages of nanoparticle formation have been established: accumulation of implanted copper in solid solution, nucleation of nanoparticles, coalescence, growth of nanoparticles, and saturation of nanocomposites.     

Radiation-induced modifications of point defects in quartz crystals and their application in radiation dosimetry

Different types of impurity-related point defects in crystalline quartz are known to exhibit various spectroscopic signals. When exposed to ionizing radiations, these defect centers get modified and new species of point defects are formed. This paper presents a study and discussion of radiation-induced modification of point defects in natural as well as cultured quartz, with an emphasis to use this material for radiation dosimetry up to a range of a few Mrad.     

Paramagnetic frenkel defects in irradiated alkali-haloid crystals

In the EPR spectra of γ-irradiated NaF,⁶LiF, and LiF crystals with natural content of isotopes (independent of the impurity composition), the hyperfine structure (HFS) is observed against the background of a broad band. Absorption saturation in the system of defects responsible for the HFS and the broadband occurs at widely different power levels of microwave radiation, and broad band suppression takes place at registration in quadrature. The experimentally measured intensity distribution and the number of EPR lines in the⁶LiF crystal correlate with the calculated data when the spin interaction of an unpaired electron with 14 equaivalent fluorine nuclei is taken into account. A model of major radiation-induced paramagnetic defects in the form of Frenkel pairs, in which one component (the negatively charged quasi-molecule consisting of two halogen atoms) can be responsible for the HFS and the other component (F-center) for the broad band in the EPR spectrum, is proposed.     

The slow component of quartz optically stimulated luminescence

The slow component of quartz OSL displays a number of properties that clearly distinguish it from the main (‘rapidly bleachable’) part of the quartz OSL signal traditionally used for dating. These properties include an extremely high thermal stability, dose saturation level and a charge concentration dependence in both signal form and decay rate. The physical mechanism responsible for the slow component is thought at present to involve a direct donor–acceptor recombination component, possibly associated with competing pathways below, and possibly up to, the conduction band. The thermal stability and high dose saturation characteristics of the slow component suggest much potential for long-range dating exists although at present it is uncertain whether difficulties associated with partial resetting may preclude routine use of the slow component for dating sedimentary deposits. A single-aliquot additive dose method was however used to obtain an estimate of D_e from the slow component for an Egyptian quartz sample that was in broad agreement with previous estimates based on the standard multiple-aliquot additive dose method.The slow component is often small in magnitude compared to the initial portion of the quartz OSL decay. However, this is not always the case and for some samples significant inaccuracies in D_e estimation may occur when deriving ages from the initial ‘rapidly bleaching’ portion of the OSL decay if the effect of the slow component is ignored or taken to be constant.     

Instability of luminescence responses in feldspar-and quartz-based paleo-dosimeters

It is shown that repeated cycles of laboratory irradiation/heating, being a component part of the majority of luminescent dating protocols, cause a change in sensitivity of quartz and feldspars. As a rule, these changes relax within one month and the sensitivity tends toward its initial value. The analysis of experimental data confirms that these phenomena are caused by thermo-and radiation-induced ionic processes and cannot be connected to tunneling. In addition, ionic processes cause an increase in the sensitivity of quartz on heating to temperatures approaching that of the phase transition in quartz (573°C). The dose sensitivity (stored or liberated light sum per unit absorbed dose) of quartz starts growing even when it is moderately heated (to about 300°C), which is typical of dating procedures. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 819–824, November–December, 2008.     

Photoluminescence of implantation-induced defects in SiO2:Pb+ glasses

The luminescence of quartz glass with implanted Pb⁺ ions is investigated by time-resolved photoluminescence spectroscopy under synchrotron excitation. It is established that the glass layer modified with ions represents a microheterogeneous medium with a variable content of implanted ions predominantly in the form of Pb²⁺. Three different types of emission centers are detected that are created by radiation-induced defects of the SiO₂ matrix and localized electronic states of the amorphous lead-silicate phase.     

Luminescence enhancement of ZnO nanoparticles on metal surface

We have studied luminescence enhancement of zinc oxide (ZnO) nanoparticles with the average size of 30 nm on several metal surfaces at low temperatures. Bandedge luminescence originated from bound exciton (BE) annihilation is observed at 3.360 eV, and strongly depends on the kind and surface roughness of metal. The luminescence intensity is about 10 times larger for Ag surface than that for quartz surface. Furthermore, the luminescence increases remarkably when the roughness of Ag surface is almost the same as the particle size. The intensity ratio of the fast decay component to the slow one decreases for Ag surface compared with quartz. These results suggest that the luminescence enhancement is partially attributed to suppressing of the nonradiative recombination process in ZnO nanoparticles on metal surface.     

Photoelectron spectroscopy of E′ centers in crystalline and glassy silicon dioxide

Radiation-induced E′ centers in SiO₂ were studied to test the possibility of applying optically stimulated electron emission (OSEE) to the spectroscopy of excited states of point defects in dielectrics. The spectral responses of the OSEE of crystalline α quartz and silica glass irradiated by 10-MeV electrons were measured and studied. It was established that volume E′ centers in the crystalline and glassy SiO₂ modifications are dominant emission-active defects. Surface E’_s (1) centers were also detected in glassy SiO₂. A model of the energy structure of E′ centers accounting for the absence of luminescence and taking into account the presence of two nonradiative (intracenter and ionization) relaxation channels is proposed. This model was used to explain the mechanism of photothermal decay of the E′ centers and to determine the ionization activation barriers and quantum yields of these centers. The emission, spectral, and kinetic parameters of the volume and surface E′ centers in glassy SiO₂ were obtained, showing the excited states of these defects to have identical atomic configurations.     

Relaxation of radiation-induced defects in CuO

The relaxation of radiation-induced defects in the CuO polycrystal and nanoceramic with the particle size d = 15 nm irradiated by an electron dose of F = 5 × 10¹⁸ cm^?2 has been studied. In the irradiated samples, a strong susceptibility increase with decreasing temperature T < 150 K is observed. This increase is due to the formation of ferromagnetic polarons in the antiferromagnetic matrix near the defects. The structural symmetry distortion makes the samples unstable. The time variations of the magnetic properties in the CuO samples prepared by different methods are compared.     

ESR study of thermal history and dating of a stone tool

Electron spin resonance (ESR) of Fe³⁺ ions and of radiation-induced centers in quartz (E’, peroxy and Al centers) was studied to distinguish between burnt and unburnt stone tools and to determine their age. The yellow stone tool with a reddish edge discovered at the paleolithic site in Kamitakamori, northern Japan, was investigated. The ESR spectrum intensity of Fe³⁺ ions around g=4.3 and the color of the material changed at 600°C and 240°C, respectively, which indicates that the red part was heated at 240–600°C. The E′ center in the red part was used for dating because isochronal annealing experiments showed low thermal stability of the Al center and overlap of broad signals at g=2.0086 onto the peroxy center. Assuming the same efficiency of defect formation in the red part as of that in the laboratory-heated material at 450°C, the obtained age of 520–770 ka is in concordance with the ages of the tephra layers at the site.     

Photoluminescence Properties of Nanoporous Nanocrystalline Carbonate-Substituted Hydroxyapatite

Luminescence characteristics of an analogue of the mineral component of dental enamel—nanocrystalline B-type carbonate-substituted calcium hydroxyapatite (CHAP)—with defects (nanopores ～2?5 nm in size) on the surface of nanocrystals are studied. It is shown that laser-induced luminescence of CHAP samples synthesized by us occurs in the region of ～515 nm (～2.4 eV) and is related to the existence of CO₃ groups substituting PO₄ groups in the CHAP lattice. It is determined that the luminescence intensity of the CHAP samples depends on the amount of structurally bound CO₃ groups and decreases with decreasing concentration of these intracenter defects in the apatite structure. The results obtained in this work are of potential importance for developing the fundamentals of precision and early detection of caries in human hard dental tissue.     

Interaction of hydrogen and deuterium with intrinsic atomic defects in high-purity electron-irradiated nickel

Abstract

High-purity nickel was irradiated with 2 MeV electrons at temperatures below 80 K to a dose of 1 × 10²³ e^?/m² in the as-prepared state and after charging with H or D. By means of magnetic after-effect measurements relaxations of anisotropic radiation-induced defects and of defect-hydrogen complexes were investigated in the temperature range between 4.2 and 500 K. The isochronal annealing behaviour of these relaxations and the isochronal recovery of the residual resistivity was measured simultaneously on the same specimens. At temperatures below the hydrogen mobility (< 160 K) in charged irradiated specimens relaxation maxima are observed at 45, 100, 115 and 140 K which show no isotope shift for H and D charging. The maxima below 160 K are explained by defect-hydrogen complexes, where radiation-induced defects reorient around immobile hydrogen atoms. Above 160 K, where hydrogen atoms get mobile, in charged irradiated specimens a broad relaxation maximum appears at 170 K which shows an inverse isotope shift for H and D charging. This 170 K maximum anneals in Stage III. A hydrogen diffusion maximum observed in charged specimens at 215 K prior to irradiation is missing after electron irradiation. The 170 K relaxation is explained by defect-hydrogen complexes, where hydrogen atoms reorient around immobile radiation-induced defects while the long-range hydrogen diffusion is suppressed by these defects. In such relaxation measurements hydrogen and deuterium atoms are used as a “probe” to investigate radiation-induced defects.     

Evolution and defect analysis of vertical graphene nanosheets

We report catalyst‐free direct synthesis of vertical graphene nanosheets (VGNs) on SiO₂/Si and quartz substrates using microwave electron cyclotron resonance – plasma enhanced chemical vapor deposition. The evolution of VGNs is studied systematically at different growth stages. Raman analysis as a function of growth time reveals that two different disorder‐induced competing mechanisms contributing to the defect band intensity. The VGNs grown on SiO₂/Si substrates predominantly consists of both vacancy‐like and hopping defects. On the other hand, the VGNs grown on quartz substrates contain mainly boundary‐like defects. X‐ray photoemission spectroscopy studies also corroborate Raman analysis in terms of defect density and vacancy‐like defects for the VGNs grown on SiO₂/Si substrates. Moreover, the grown VGNs exhibit a high optical transmittance from 95% to 78% at 550 nm and the sheet resistance varies from 30 to 2.17 kΩ/sq. depending on growth time. Copyright © 2014 John Wiley & Sons, Ltd.