Search results for "RADIATION"

Photoluminescence excited by ArF and KrF lasers and optical absorption of stishovite mono-crystal

2008

Two photoluminescence bands were found in a stishovite (silicon dioxide) mono-crystal sample under ArF (193 nm) and KrF (248 nm) excitation. The blue band is situated at 3.17 ± 0.02 eV in the case of ArF and at 3 ± 0.2 in the case of KrF. The UV band is at 4.55 ± 0.05 eV in the case of ArF and at 4.5 ± 0.05 eV in the case of KrF. The position of the UV emission band correlates with that excited by x rays. This position is 4.6 ± 0.05 eV with FWHM 0.8 ± 0.05 eV (Truhins et al 2003 Solid State Commun. 127 415). The blue band possesses slow decay kinetics with time constant 16 ± 2 µs and the UV band is fast on the level of 2 ± 0.5 ns, similarly for both lasers. Thermal quenching of both bands b…

Annealing of Radiation Defects in X-Irradiated LiBaF3

2002

AbstractResults of application of the glow rate technique GRT for analysis of the activation energy of thermostimulated annealing of X-ray created F-type color centers in LiBaF3 crystals, pure and containing hetero-valence oxygen centers are presented. It is shown that depending on impurity composition in crystal two alternative mechanisms are involved in annealing of color centers. It is proposed that either the anion vacancy governed migration of F- centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine (Fi) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F- type …

<title>Formation of dislocations and hardening of LiF crystals irradiated with energetic Au, Bi, Pb, and S ions</title>

2003

The irradiation of LiF crystals with Au, Pb, Bi, and S ions in the range of 400 - 2200 MeV leads to a remarkable increase of the hardness. The effect appears for Bi and Pb ions at fluences above 109 ions/cm2 and for S ions above 1010 ions/cm2. The increase of hardness follows the energy loss and is related to the formation of defects along the ion path. Defect complexes, clusters and aggregates with nanoscale dimensions serve as strong obstacles for dislocations and cause dispersion strengthening. Structural investigations reveal the generation of long-range stress in the adjacent non-irradiated part of the crystal. Close to the implantation zone, the stress exceeds the yield strength, caus…

Time-dependent alignment of molecules trapped in octahedral crystal fields.

2006

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadia…

Tracks induced in TeO2 by heavy ions at low velocities

2000

On the basis of its thermal properties, TeO2 crystal was selected as an insulator with low threshold electronic stopping power for track formation Set. The crystals were irradiated by S, Zn, Mo, Kr, Te and Pb ions and the optical absorption and track formation were studied. Comparison is made with the published results on LiNbO3 ,Y 3Fe5O12 and SiO2 quartz. Good quantitative agreement is found with the predictions of the thermal spike model of Szenes with respect to Set and the variation of the track size with the electronic stopping power Se. It is shown that TeO2 has a high eAciency g at low ion velocities, which is a characteristic feature of the damage cross-section velocity eAect. ” 200…

Photostimulated emission of KBr—In previously exposed to UV- or X-radiation

1995

Abstract We have performed a photostimulated luminescence (PSL) study of a KBr—In crystal previously irradiated in the exciton fundamental absorption band. It is shown that the PSL arises from three types of close defect pair. It is also shown that one of these three kinds of defect pairs is {F, In2+}, whereas the electron centre of the two other pairs has a more complex nature.

Hardening and formation of dislocation structures in LiF crystals irradiated with MeV–GeV ions

2002

Abstract Material modifications of LiF crystals irradiated with Au, Pb and Bi ions of MeV to GeV energy are studied by means of microindentation measurements and dislocation etching. Above a critical irradiation fluence of 10 9 ions/cm 2 , the microhardness can improve by a factor of 2 in the bulk and by more than 3 on the surface. Radiation-induced hardening follows the evolution of the energy loss along the ion path. Annealing experiments indicate that complex defect aggregates created in the tracks play a major role for the hardness change. Evidence for severe structural modifications is found when etching indentation impressions in highly irradiated crystals leading to similar pattern a…

<title>Nature of fundamental absorption edge of WO<formula><inf><roman>3</roman></inf></formula></title&…

1997

The fundamental absorption edge of amorphous, polycrystalline and crystalline tungsten trioxide (WO3) thin films obtained by different techniques (thermal evaporation, rf plasma sputtering, chemical gas transport) was investigated. Special attention was paid to correct measurements of absorption values of all WO3 thin films taking into account the scattered light, interference effects and reflection losses. The indirect edge at 2.70 eV was determined for crystalline WO3, but for crystal WO3:Ti the direct edge in the same place (2.72 eV) was found. For polycrystalline WO3 thin film first edge transition located at 2.76 eV had a quadratic dependence similar to the amorphous film at a higher p…

Transient Optical Absorption and Luminescence in Calcium Tungstate Crystal

2001

<title>Optical properties of hydrogen-containing MgO crystal</title>

2008

The photoluminescence (PL), its excitation (PLE) and absorption spectra in ultraviolet, visible and infrared (UV-VIS-IR) regions were used to investigate the MgO single crystals irradiated by fast neutrons. It is shown that the photoluminescence band of the MgO crystals at 730 nm belongs to the hydrogen-containing complex centers V-OH-Fe3+, which are transformed during the irradiation with fast neutrons. The behavior of the PL band 730 nm after fast neutron irradiation depends on the iron-chromium concentration. It is found that the fast neutron irradiation produces the interstitial proton H+i and the Mg(OH)2 microphase.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineer…