Ludmila A. Lisitsyna

Nanodefect substructures in crystal phosphors

We investigated spectral and kinetic characteristics of the luminescence in alkali halide crystals with polyvalent impurities, crystal phosphors based on metal tungstates in the form of nano-, micro- and bulk crystals. The possibility of the existence of complex defects (nanodefects) in materials containing high defect concentration is shown.

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.

Pulsed Cathodoluminescence of ZnWO4:Eu Single Crystals and Nanocrystals

Pulsed cathodoluminescence of zinc tungstate samples doped with europium in the form of single crystals and nanocrystals in the transparent organosilicic matrix is studied. The effect of the size of the crystal on spectral and kinetic parameters of the oxygen luminescence centers is interpreted within the model of self-organization of activator nanodefects during crystal growing.

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.

Kinetics of the cathodoluminescence flash in crystals with competing trapping centres

The present work aims to bring proof of possibility of the existence of the process to increase the number of luminescence centers in the radiative state. That apparently has the effect of the buildup of luminescence excited by a pulsed electron beam. To demonstrate the possible influence of competing centers on the decay kinetics of luminescence materials were selected on the basis of crystal YLiF4 and YLiF4: Nd3+. Found that the kinetics of flash luminescence when excited LiYF4: Nd crystals pulse electron beam at room temperature in the initial stage of a flare- up of up to 300 ns was observed. The model of the exchange of electronic excitations between the centers of the emission and capture is discussed.

Features of F2 Сenters Accumulation in Oxygen-Containing LiF Crystals

A mechanism for correlated formation of intrinsic defects F2 centers and impurity hole centers with hydrogen bond in oxygen-containing LiF crystals is suggested.

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.