A. Dauletbekova

Pulsed photo- and cathodoluminescence of LiF crystals doped with tungsten oxide

We have studied the spectral and kinetic characteristics of activated photo- and cathodoluminescence of LiF-O and LiF-WO3 crystals in the spectral range of 3.6–1.6 eV using methods of pulsed spectrometry with nanosecond time resolution in the temperature range of 15–300 K and in the range of ionizing radiation dose absorbed by crystals of 102−2 × 103 Gy.

Impurity cathodoluminescence of oxygen-containing LiF crystals

Cathodoluminescence of oxygen-containing LiF crystals (LiF-O, LiF-O,OH, LiF-WO3) is studied by pulsed spectrometry with nanosecond resolution upon excitation of crystals by a single electronbeam pulse at 15 K.

Ab initio calculations of the atomic and electronic structure of MgF2 (011) and (111) surfaces

The results of ab initio slab calculations of surface relaxations, rumplings and charge distribution for the different terminations of the MgF2 (011) and (111) polar surfaces are presented and discussed. We have employed the computer code CRYSTAL with the Gaussian basis set and the hybrid B3PW exchange-correlation functional. Despite the ionic nature of the chemical bonding at both surfaces, a considerable decrease of the optical band gap is predicted (1.3 eV or 10%) for the (111) surface as compared to the bulk.

Color centers and structural damage in LiF induced by 150 MeV Kr ions

Color centers and evolution of structure defects were investigated in LiF crystals irradiated at room temperature with 150 MeV 84Kr ions with a beam current of 10nA/cm2 in the fluence range 1011 - 1014 ions/cm2 at the cyclotron accelerator DC-60 (Astana, Kazakhstan). At the fluence of 1011 ions/cm2, SEM imaging revealed mainly formation of etchable ion tracks. Above this fluence, severe structural modifications in the irradiated layer were observed which include the ion-induced formation of dislocations and grains with nano-scale dimensions. The role of fluence in the concentration of electronic color centers and structural modifications is discussed.

Cathodoluminescence and Radiation-Induced Absorption in YLiF4 Crystals in Excitation by Electron Pulse

The paper presents the experimental results for the spectra of the luminescence burst and induced optical transient absorption in YLiF4 crystals when exposed to the electron pulse of nanosecond duration over a wide temperature range. The luminescence spectrum consists of two bands with peaks at 4.4 and 3.2 eV, and in the spectrum of induced absorption the main bands are found at 2.1 and 3.7 eV. The luminescence at 3.2 eV decays faster than the bandwidth at 4.4 eV. The luminescence intensity decreases sharply at temperatures above 30 K. The induced absorption decreases at temperatures above 60 K. It is assumed that the kinetic curves of luminescence burst and transient absorption in excitation by radiation fluxes are related.

Modification of LiF structure by irradiation with swift heavy ions under oblique incidence

The structural modifications of LiF irradiated with swift heavy ions under oblique angles have been investigated using AFM, SEM, chemical etching, nanoindentation and optical absorption spectroscopy. LiF crystals were irradiated under incidence angles of 30 and 70 degrees with 2.2 GeV Au (fluence 57?l011 ions-cm2) and 150 MeV Kr ions (fluence 1012?1014 ions?cm?2). Structural study on sample cross-sections shows that two damage regions ? (1) nanostructured zone and (2) dislocation ? rich zone, which are typical for irradiations at normal incidence, appear also in samples irradiated under oblique angles. However in the latter case a more complex structure is formed that leads to stronger ion-induced hardening.

Pulsed Cathodoluminescence of F 2 Centers in Undoped and Doped LiF Crystals

This work examines the generation of F2 centers in LiF, LiF〈O,OH〉, and LiF:U〈O,OH〉 crystals by electron pulses at 300 K. We discuss nanosecond and microsecond mechanisms for the excitation of pulsed cathodoluminescence of F2 centers in the crystals.

Effects of Doped Oxygen on ZnWO4 Crystal Luminescence

The results of the study of the spectral characteristics and photo cathodoluminescence zinc tungstate crystals subjected to heat treatment in an oxygen atmosphere, or flows of high-energy irradiation of oxygen ions. It was observed that additional introduction of oxygen leads to decline in luminescence’s effectiveness. It was discovered, that introduction of oxygen by thermal processing leads to changes in excitation spectrum. Decline of excitation effectiveness proportional to increase of excitation quanta energy from 4.5 to 6.5 eV was observed; in the meantime, in the unprocessed crystals it declined by only 25-30%. The effect can be explained by destruction of complex defects with luminescence centers during introduction of additional oxygen. It was demonstrated, that characteristic oxygen’s depth of entry during thermal processing is 20 nm.

Stability of color centers in LiYF4 crystals at low temperatures

This paper presents the results of examining the stability of induced radiation defects in crystals at 15K. The following regularities have been established. Defects induced at low temperatures in pure and Nd 3+ doped LiYF4 crystals are unstable: upon termination of radiation, even at 15K induced color centers are visibly destructed, exposure to the halogen lamp light increases the destruction speed significantly. Heating crystals up to 80K results in complete destruction of color centers induced at 15К.

Kr and Xe ion induced aggregation processes in LiF crystals during irradiation and thermal annealing

The efficiency of F and Fn center creation in LiF crystals irradiated with 147 MeV Kr and 195 MeV ions was studied via ion fluence and flux. In the case of Kr ions with flux of 8.9×10 9 ions/(cm 2 ×s) saturation of F centers (~ 10 19 cm -3 ) was observed at a fluence of 10 12 ions/cm 2 . Further irradiation decrease the F center concentration. In LiF irradiated with both ions an enhancement of electron color centers (F and Fn) via flux was observed. In LiF crystals irradiated with Kr ions an enhancement of Fn centers was observed after thermal annealing up to 600 K. The mechanisms of the processes are discussed.