[en] Lithium fluoride nanocrystals are irradiated by gamma quanta at 77 K. The radiation color centers formed in a near-surface layer of nanocrystals are studied. Absorption, luminescence and luminescence excitation spectra of the surface defects have been measured. It has been found that the luminescence excitation spectra for aggregated surface centers consist of two or three bands with not very much different intensities. Reactions of the surface centers separately with electrons and with anion vacancies have been investigated. Numbers of anion vacancies and electrons entering into the centers composition have been established and it has been found that F_S1, F_S1⁻, F_S2, F_S2⁻, F_S3⁺ and F_S3 types of the surface centers are formed. The degree of luminescence polarization has been defined and it has been determined that the polarization degree for F_S2⁺ centers changes sign under transition from one excitation band to another. It has been shown that during irradiation at 77 K radiation-induced defects are formed more efficiently on the surface than in the bulk. - Highlights: • Radiative color centers were fabricated in lithium fluoride nanocrystals. • The unique absorption and luminescence characteristics are inherent in the centers. • The reactions of these centers with electrons and anion vacancies were studied. • The degree of luminescence polarization was defined. • Numbers of anion vacancies and electrons forming the centers were established

[en] In this article we present the results of development of non epitaxially grown thin-film LiF and CaF₂ structures for elaborating integrated light-emitting elements with ultrabroadband continuously-tunable spectra in the region 500-700 nm. The space ordering of emitting defects as well as their luminescence efficiency in such elements were technologically controlled by the ordering of radiation-sensitive crystals in preformed thin-film structures and by post-growth gamma-irradiation. The modification of the room-temperature emission spectra of γ-irradiated thin-film structures consisting of nanometer-sized LiF or CaF₂ crystals is investigated. The results are compared with those obtained for LiF and CaF₂ nominally-pure single-crystals after the same dose of irradiation. Possible origin of the effect is discussed. (authors)

[en] We have studied characteristic features of photoinduced processes occurring in CdSe/ZnS semiconductor nanocrystals on prolonged exposure to ultraviolet light in air and under vacuum. Accelerated photodegradation of the nanocrystals in air has been established, associated with photooxidation. (authors)

[en] A method is developed for determining the mean lifetime of anion vacancies in dielectric crystals following irradiation. This method is used to study the temporal kinetics of the concentrations of vacancies and F²⁺ color centers in lithium fluoride crystals irradiated by ionizing radiation. It is then possible to study the dependences of the vacancy lifetime on the concentration of F¹ color centers, temperature, and impurity content of a crystal. Vacancy and F²⁺ color lifetimes determined by this method are given. (authors)

[en] It has been shown that in spatial structures based on color centers produced by electrons in a crystal of lithium fluoride, distances between centers reach 1.6 and 3.6 nm for centers F₁ and F₂ accordingly. This is the evidence for great potentialities of applying electronic technologies for defects creation in crystals to form structures with the spatial resolution of such an order. A decrease in the fluorine content at the irradiated crystal surface was measured. Concentrations of centers F₁, F₂, F₃⁺, F₃ (R₂), and F₄ (N₁) were found. As was established, the specific character of production of color centers by electrons causes the increase in the efficiency of F₃ and F₄ centers formation. Reduction in average luminescence lifetimes of F₂ and F₃⁺ centers caused by a concentration quenching was found. Distortion of a luminescence contour of F₂ centers as a result of both the absorption of its short-wave part by other centers and the radiation emitted by them to its long-wave part was revealed (authors)

[en] Isobestic and isoemission points are recorded in the combined absorption and luminescence spectra of two types of radiation defects involved in complex processes consisting of several simultaneous parallel and sequential reactions. These points are observed if a constant sum of two terms, each formed by the product of the concentration of the corresponding defect and a characteristic integral coefficient associated with it, is conserved. The complicated processes involved in the transformation of radiation defects in lithium fluoride are studied using these points. It is found that the ratio of the changes in the concentrations of one of the components and the reaction product remains constant in the course of several simultaneous reactions. (authors)

[en] The effect of external electric fields on the photoluminescence of quantum-sized nanocrystals of cadmium selenide excited by photons of various energies is studied. Photoluminescence quenching by external electric fields is found to be different for nanoparticles with different shapes (quantum dots and nanorods) and does not depend on the exciting photon energy. The relationship between the strength of the external electric field and the degree of quenching is determined empirically for both types of nanoparticles. A possible mechanism for the effect of an external electric field on the excitation and quenching of photoluminescence in quantumsized nanoparticles is discussed. (authors)

[en] We have developed a method for quantitative luminescent analysis of multicomponent media. To carry out this method, we need to use a standard luminescent probe and have overlap between the luminescence excitation spectra of the probe and the analyte substance. We have shown that the method is applicable for analysis of scattering media with different absorption optical densities, including optically dense media. We have demonstrated that it is invariant relative to changes in the experimental geometry and the parameters of the medium. A broad range of measurable values is characteristic of the method. Its sensitivity is determined by the sensitivity of the luminescence intensity measurements. We have determined concentrations of organic substances in the range ∼10-10 to 10-11 g/cm³. (authors)

[en] Luminescence and luminescence excitation spectra are recorded for surface radiation-induced defects in lithium fluoride at temperatures of 77 and 293 K. The presence of three bands with relatively small intensity differences is a distinctive feature of the excitation spectrum. These bands are found to belong to the same type of defects. The positions of the peaks and the widths of the absorption and luminescence bands for these defects are determined. The luminescence decay time is measured. All the measured characteristics of these surface defects differ from those of previously known defects induced by radiation in the bulk of the crystals. It is found that the luminescence of surface defects in an ensemble of nanocrystals with different orientations is not polarized. The number of anion vacancies in the surface defects is estimated using the polarization measurements. It is shown that radiative scattering distorts the intensity ratios of the luminescence excitation bands located in different spectral regions. (author)

[en] We have demonstrated a difference in the nature of the effect of a strong external electric field (>10⁵ V/cm) on the photoluminescence of cadmium selenide nanoparticles of different shapes. We have determined a correlation between the magnitude of the external electric field and the average photoluminescence decay time for two types of nanoparticles: 'quantum dots' and nanorods. We discuss the mechanism for the effect of an electric field on the photoluminescence of both types of nanoparticles. (authors)