Search results for "Alkali metal"

Muon knight shift measurements in the alkali and alkaline earth metal series

1979

The kinetics of diffusion-controlled annealing of Frenkel defects in alkali halide crystals

1994

Abstract The annealing kinetics of the strongly correlated (the so-called geminate) pairs of both neutral F,H centers as well as F, I centers entering secondary triplets (F…Ihellip; self-trapped hole) in KCl and KBr crystals is calculated. In this model diffusion of hole I and H centers and their annihilation with electron F centers at short relative distances stimulated by the elastic or Coulomb interaction are taken into account. It is demonstrated that F,H pairs are destroyed by tunneling recombination already at times ≤ 10−4 s, i.e. much before the beginning of the thermostimulated experiments. A possible explanation of this contradiction is discussed.

Theoretical simulations of the radiation-induced defect processes in insulating materials

1994

Abstract The results of two basic kinds of computer simulations of radiation-induced processes in insulating materials, one based on quantum-mechanical and pair-potential (atomistic) approaches, and the other a phenomenological theory of diffusion-controlled reactions, are presented. It is shown that, by combining different techniques (atom-atom potentials and semi-empirical quantum chemical methods) the optimized geometry and the electronic structure of a family of hole centres in crystalline corundum (α-Al2O3) could be found. Their energetics are analyzed; V2−, V−V−Mg hole centres all have a common basic element, namely the diatomic molecule O23−, which is responsible for their similar ab…

Basic properties of the F-type centers in halides, oxides and perovskites

2010

We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO3 perovskites. We discuss in details the optical properties of single electron F and F + centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo–Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin–Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali hal…

Radiation defects in doped alkali halide microstructures

2000

Abstract Photostimulated luminescence (PSL) has been measured in KBr and KI systems doped with Tl and In. The size of grains in microstructures varied from 0.1 to 1.0 μm. Specifics of the photostimulated luminescence mechanisms in these systems are analysed from the viewpoint of their application in miniaturized optoelectronic and photonic devices, including optical chips.

Modelling of point defects in α-AL2O3

1995

Abstract The semiempirical method of the Intermediate Neglect of Differential Overlap (INDO), in the program SYMSYM, has been used for calculations on perfect and imperfect corundum crystals. For the perfect crystal the periodical Large Unit Cell (LUC) model was used while the Molecular Cluster (MC) model was used in defect calculations. By means of the MC model, we have investigated the optical properties of electronic centers (F+, F, F−, FMg, F− Mg) in corundum. Calculated optical properties of these defects are compared with experimental values and new bands are predicted to exist in the absorption spectrum of Mg-doped corundum. The energy levels of F-type and Mg-impurity related centers…

Self-trapped exciton luminescence in α-quartz

1994

Abstract It is shown that two differently oriented (perpendicular and parallel to the c axis) serf-trapped excitons (STE ⊥ and STE ∥ ) can be created in the range of the Urbach tail of the fundamental absorption of α-quartz. Below this tail no STE luminescence was found. The alkali ion centers, excited below the tail, give luminescence bands, which can be replaced by substituting alkali ions with Cu + ions. It is concluded that both STE ∥ and STE ⊥ are intrinsic.

Evidence for anI=1 isomeric state in96Rb

1981

Aβ-RADOP (β-Radiation Detected Optical Pumping) experiment on the short lived (T1/2=203 ms)96Rb isotope has been performed at the on line mass separator for fission produced alkali isotopes at the TRIGA reactor in Mainz. Irradiation of r.f. onto the polarized sample to induce Zeeman transitions resulted in two signals for nuclear spinsI=2 andI=1. The previously undetermined component withI=1 is interpreted as evidence for an isomeric state in96Rb.

Doped Alkali Halide Thin Films as Active Media for Information Storage and Retrieval

1997

Interlocking inorganic screw helices: synthesis, structure, and magnetism of the novel framework uranium orthothiophoshates A11U7(PS4)13 (A = K, Rb).

2002

The novel quaternary uranium thiophosphate K11U7(PS4)13 has been synthesized by reacting uranium metal, K2S, S, and P2S5 at 700 degrees C in an evacuated silica tube. The crystal structure was determined by single crystal X-ray diffraction techniques. K11U7(PS4)13 crystallizes in the tetragonal space group I42d (a = 32.048(2) A, c = 17.321(1) A, Z = 8). The structure contains a tunnel framework composed of eight interlocking uranium U7(PS4)13 screw helices, with alkali metal cations residing inside the framework channels. The uranium atoms are coordinated in a bi- or tricapped trigonal prismatic fashion. The screw helices are built up from uranium atoms interconnected by PS4 tetrahedral uni…