Radioluminescence of synthetic quartz related to alkali ions

The radioluminescence (RL) of synthetic quartzes (GEMMA Quartz & Crystal Company) has been measured at room temperature. Some samples were treated by electrodiffusion (“sweeping”) in order to change the concentrations of alkali ions, mainly Li⁺ and Na⁺, which in quartz are known to be linked to Al ions, substitutional for Si ions.The RL emission spectra show evidence of a role of alkali ions in affecting some specific emissions. All the spectra could be analysed as composed of four bands in the blue and UV region. Specifically, the well known blue emission at around 470 nm was seen to be composed by two bands at 430 nm (2.86 eV) and at 485 nm (2.53 eV). Effects of irradiation, during the RL measurements, were clearly seen only in the “Li swept in” sample, namely an increase in the 485 nm band intensity and a decrease in the 430 nm band one. The previously reported UV emission was detected at 355 nm (3.44 eV) in all the samples, being the most intense band in the “swept out” sample. A further UV emission was detected at 315 nm (3.94 eV), more intense in untreated samples.Possible assignments of the detected emission bands are discussed in relation to the defects of quartz, specifically focusing on the Al centres that are most affected by sweeping procedures.     

The role of halide ions on the electrochemical behaviour of iron in alkali solutions

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.     

Boson peak measurements in neutron-irradiated quartz crystals

We have measured the low-frequency Raman scattering in neutron-irradiated quartz crystals with four different irradiation doses from 4.7×10¹⁹ n/cm² to 1×10²⁰ n/cm² and for 2 different crystallographic directions. For the used doses the range of density change of the investigated samples was 12% (the maximum change during amorphization is 14%) and the amorphous fraction varied from 35% to 100%. The same measurement was done in neutron-irradiated amorphous silica with a maximal dose 2×10²⁰ n/cm². In all cases we observed the boson peak in the Raman spectra. The position of the peak, at 67±3 cm^-1, was found to be the same for all the investigated samples independent of the dose. The shape of the peak for doses 6.8× 10¹⁹ n/cm² and higher was also found to be the same for 5 investigated samples (including irradiated vitreous silica). We found that the position of the boson peak in neutron-irradiated quartz crystals and vitreous silica corresponds to the Ioffe-Regel crossover frequency for phonons. The origin of the boson peak in neutron-irradiated quartz and vitreous silica can be attributed to local soft optic modes, which are analogous to the soft optic mode that drives the α–β transition in quartz.     

Thermally Stimulated Luminescence (TSL) and Conductivity (TSC) of synthetic crystalline quartz

A comparative and simultaneous study of TSL and TSC above room temperature (20–400°C) has been performed on “as-grown” and “hydrogen-swept” synthetic quartz crystals. Following X- irradiations, TSL spectra (heating RATE = 1°C/s) feature a number of peaks: at 75°C an intense structure is observed (the well-known “100°C” peak of quartz); the analysis of this peak obtained by numerical methods has shown that it follows monomolecular kinetics, giving a value of 0.83 eV for the trap depth. Additional peaks are observed at 110°C and 160°C, followed by weaker and less resolved emissions above 200°C. TSC peaks at 80°C, 120°C and 160°C, particularly evident in as-grown samples when measured with the electric field applied along the x-axis, can be associated to the corresponding TSL peaks. However, spectra performed with the electric field applied along the z-axis evidence different features. In as-grown samples a strong and broad peak at approximately 132°C is observed, while hydrogen-swept samples are characterized by two peaks at 180°C and 275°C. Such an anisotropic character, and the fact that no TSL structures are observed in the same temperature range, support the hyporthesis of an ionic nature for the latter peaks. TSC “pre-dose” measurements of the 75°C peak show that no current enhancement is observed upon irradiational and heating treatment: this result is in accordance with previous radioluminescence and thermally stimulated exoelectron emission experiments and supports the proposed model of the dynamics of this effect.     

Photodetachment measurements of alkali negative ions

Cross sections of alkali negative ions from 0.45 eV up to about 2.5 eV photon energy were measured. Electron affinities of the corresponding atoms are derived from the low energy onsets: EA(Li)=0.611 eV, EA(Na)=0.539 eV, EA(K)=0.497 eV, EA(Rb)=0.490 eV and EA(Cs)=0.470 eV with an estimated uncertainty of ±0.020 eV.     

Electronic polarisabilities of ions in alkali halide crystals

Tessman, Kahn and Shockley calculated the electronic polarisabilities of ions in alkali halide crystals using the long wavelength limiting values of the visible light dielectric constants. We have recalculated these widely used polarisabilities using the more accurate room-temperature dielectric constant data of Lowndes and Martin and a better minimisation procedure of Pirenne and Kartheuser. We have also calculated for the first time the low temperature values of these polarisabilities. The computed values of the polarisability in ų are Li⁺ 0·029, Na⁺ 0·285, K⁺ 1·149, Rb⁺ 1·707, Cs⁺ 2·789, F^? 0·876, Cl^? 3·005, Br^? 4·168, I^? 6·294 at 300°K and Li⁺ 0·029, Na⁺ 0·290, K⁺ 1·133, Rb⁺ 1·679, Cs⁺ 2·743, F^? 0·858, Cl^? 2·947, Br^? 4·091, I^? 6·116 at 4°K. The relative standard deviations for all the alkali halides are 1·20 and 1·43 per cent at 300°K and 4°K respectively justifying the additive nature of the individual ion polarisabilities.     

Luminescence of quartz activated with manganese ions

Russian Physics Journal -     

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 migration of alkali metal (Na+, Li+, and K+) ions in single crystalline vanadate nanowires: Rasch-Hinrichsen resistivity

We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li₄V₁₀O₂₇), Na-vanadate (NaV₆O₁₅), and K-vanadate (KV₄O₁₀) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides(V(OH)₃) nanoparticles containing Li⁺, Na⁺, and K⁺ ions and further the analysis of the migration of charged particles (Li⁺, Na⁺, and K⁺) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V₂O₅, resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature.     

The far infrared transmission of crystal quartz at 3 K

We present transmission measurements of Z-cut crystal quartz at 3 K in the wavenumber range 60–180 cm⁻¹. The results show that the absorption is extremely small and in fact on the average a factor of ten smaller than indicated by earlier measurements discussed in the literature. One consequence of our results is that crystal quartz is useful in the FIR as a substrate material for Fabry-Perot meshes used in cryogenic experiments.     

Observation of negative alkali ions from alkali halides during 248-nm laser irradiation

Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected. Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation by the sequential attachment of two electrons to K⁺. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest that negative ion formation involves a similar mechanism.     

The ‘110°C’ TL peak in synthetic quartz

The thermoluminescence (TL) of synthetic quartz has been investigated in the temperature region 275–475 K. These measurements have revealed a more complicated structure of the 110°C TL peak and thermal activation energies and frequency factors have been estimated for a number of peaks within the glow curve. The results obtained after annealing samples in different atmospheres indicate that oxygen-related defects play an important role in the luminescence process, involving both the charge traps and recombination centres.     

Calculation of binding energy in negative ions of alkali elements

The binding energy of an electron to negative ions of the alkali elements Li, Na, K, Rb, Cs, and Fr is calculated on the basis of the formalism of the polarization potential and relativistic perturbation theory with the model zero-approximation potential. The results that are obtained refine data available in the literature for these negative ions. Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 70–74, February, 1998.     

The role of dislocations in radiation strenghtening of alkali halide crystals

The dependence of activation volume and dislocation start stress in sodium and calcium chloride crystals on-radiation dosage (in the range 10⁴–10⁹rad) is studied. It is established that these functions indicate that the hardening of crystals subjected to radiation is of a dislocation nature. Analysis of data from the literature leads to the conclusion that in the medium and high radiation dose region planar precipitates and surrounding dislocations formed by halogen molecules are responsible for hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 99–103, June, 1976.     

Absorption bands of lead in alkali chlorides in the presence of hydroxyl ions

Absorption studies of divalent lead in crystals and solutions of alkali chlorides with an admixture of hydroxyl ions showed that the absorption band lying at 250 nm can be attributed to hydroxochlorocomplexes of lead.It is the author's agreeable duty to thank Dr. A. Bohun for having drawn his attention to this problem and V. Piskáková for help in the absorption measurements.     

A peak structure in isothermal luminescence signals in quartz: Origin and implications

Isothermal heating is commonly used in luminescence dosimetry and trap parameter studies. It is often observed that the isothermal luminescence signal has a peak shape instead of a monotonous decay form. We provide here evidence that this peak shape in quartz may equally result from a ‘thermal lag’ problem in contrast to the earlier propositions of non first-order kinetics. Temperature modelling suggests that the peak-shaped signal contains elements of both the ramped — and isothermal — thermoluminescence (TL). The modelled changes in the peak movement as a function of isothermal temperature and the ramp-rate show an excellent agreement with those obtained experimentally. This understanding of thermal lag is extended to optically stimulated luminescence (OSL) measurements for which the effects of isothermal TL contamination and changing thermal assistance during thermal equilibration are discussed. Appropriate methods are suggested to identify thermal lag on the basis of the peak structure, and to circumvent this effect in isothermal methods.     

Off-centre position of excited s2 ions in alkali halides

Abstract

Off-centre displacement of Ga⁺ and In⁺ ions in the triplet relaxed excited state, occurring in the plane perpendicular to the tetragonal Jahn-Teller distortion axis of the centre, has been found. This effect may be caused by the vibronic mixing of the one-electron triplet relaxed excited state of (ns) (np) configuration with two-electron triplet excited states of (np) (np) configuration. Some experimental manifestations of the latter states have been detected.