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Two types of thermally unstable U1 centers are created in LiF:Mg,OH crystals by γ−irradiation at low temperatures. One of them is influenced by impurity complexes containing magnesium ions Mg2+. Another type of U1 center is perturbed by impurities of OH¯ ions. Temporal dynamics of conversion of U1 centers and F2+ and F2+** color centers after crystal was heated from temperature of 80 K to 300 K is presented. [ABSTRACT FROM AUTHOR]

The results of the study of the parameters of the surface layer of a LiF crystal irradiated by Ag or Cu ion beam through a metal mask in the form of a grid with a period of 7 µm are presented. It was shown that a composite layer with a thickness of 3–5 µm is formed in the crystal in the form of a periodic structure containing F2 and F3+ color centers and (sub)nanometer metal particles. A diffraction pattern is observed on this structure upon irradiation with a laser beam. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) were synthesized of glucose solution by microplasma treatment at atmospheric pressure and room temperature. The spectral-kinetic properties of the synthesized CQDs were studied use of MicroTime 200 confocal scanning luminescence microscope. СQDs have a wide emission spectrum in 400–750 nm area when excited by light with wavelength in the 375–530 nm range. CQD exhibit a bright radiation in the blue range. The concentration of quantum dots was controlled by varying the time of microplasma treatment of glucose solution. The time-resolved fluorescence decay curve was measured by the time-correlated single photon counting (TCSPC) method. Studies of luminescence kinetics revealed three exponential components with decay time constants equal to 0.65, 2.2, and 6.2 ns. The formation of these components is presumably associated with the quantum confinement effect and with presence of different functional groups between which quantum transitions take place. [ABSTRACT FROM AUTHOR]

Studies of the process of electret charge generation in LiF crystals subjected to mechanical activation and evaluation of the role of color centers in this process were carried out. Accumulation of currents in the studied material in absence of external voltage is connected with electrical activity of the system and the generation of a stable internal electric field in this system. The electric field generated in a heterogeneous medium formed by fine-dispersed lithium fluoride and a water film, causes ionization of polar water molecules that produce conductivity channels. This leads to active electrical interaction of the surfaces of solid and liquid dielectrics included in structure of the system under study. The presence of radiation induced defects in the dispersed phase based on LiF influences the processes of interphase interactions. This contributes to formation of deep electron traps and increases the lifetime of the charge of electrets. [ABSTRACT FROM AUTHOR]

The optical spectra of BaBrI crystals activated by divalent samarium were studied. The samples exhibit bright luminescence in the red region of spectra due to 4f6–4f6 and 4f55d1–4f6 transitions of Sm2+ ions. Luminescence exhibits strong temperature dependence in the range 7–300 K. At low temperatures, luminescence associated with parity-forbidden 4f6–46f transitions from 5D0 and 5D1 states is observed. Coloring of the crystals after irradiation by ultraviolet light and long afterglow luminescence of BaBrI:Sm2+ were detected. [ABSTRACT FROM AUTHOR]

Low-temperature absorption spectra at temperatures of range of 7.2–300 K in MgF2 and LiF-O,OH crystals were studied to investigate the electron-phonon interaction of radiation-induced color centers in these crystals. The coupling strength (S) with the phonons of the lattice of electronic-vibrational transitions was determined from the ratio of intensities in the zero-phonon line and the integrated absorption band. The nature of the color centers associated eith the absorption band at 390 nm and the emission at 490 nm in LiF-O,OH crystals and for the absorption band at 370 nm and the emission at 420 nm in MgF2 crystals was determined from value of S. [ABSTRACT FROM AUTHOR]

This paper presents the results of ab initio calculations of F centers in a number of crystals of mixed barium halides. The calculations were performed using the density functional method and the PBE0 hybrid functional. On the basis of the calculation results, layout of the location of the main levels of F centers in the band gap of the crystals under study was made. [ABSTRACT FROM AUTHOR]

This work is devoted to studies of the efficiency of creation and diversity of molecular complexes with the strong hydrogen bond OHF in γ-irradiated LiF and NaF crystals depending on the type of magnesium-hydroxyl impurity complexes. Infrared (IR) spectroscopy studies have shown that the concentration of Mg2+OH¯OH¯Vc¯ complexes increases as the percentage of magnesium added to the melt increases. Increase in the concentration of Mg2+ OH¯OH¯Vc ¯complexes leads to increase in the intensity of the IR bands in the region of 3550–3700 cm–1 in unirradiated crystals. As a result, the radiation-induced IR bands of complexes with a strong hydrogen bond in the range of 1600–2400 cm−1 are shifted towards lower frequencies. The radiation-induced IR bands of complexes with strong hydrogen bond OHF in the region of 1600–2400 cm−1 are shifted towards high frequencies in the presence of a hydroxyl impurity in the crystal in the form of "free" OH¯ ions with the absorption band at νmax = 3730 cm-1. Such shifts also occur at different irradiation doses. [ABSTRACT FROM AUTHOR]

A numerical model of filamentation of train of femtosecond laser pulses in solid transparent dielectrics accounting for heat accumulation is developed. [ABSTRACT FROM AUTHOR]

A theoretical estimation of local heating of a material during single and multiple filamentation of series of femtosecond laser pulses in a LiF crystal is obtained. [ABSTRACT FROM AUTHOR]

We propose a polarizing interferometer based on a crystal anisotropic medium with variable thickness. The results of experimental simulation modelling show that this interferometer can be used to measure the coherence time in a wide time range from a few femtoseconds to tens of picoseconds. This can be used, for example, to control the picosecond pedestal of spectrally limited femtosecond pulses. [ABSTRACT FROM AUTHOR]

Studies of the photoluminescence spectra of γ-irradiated lithium fluoride crystals during temperature annealing in the temperature range from 50 to 490°C were conducted. Experimental data show that F2 and F3+ color centers decay at different rates as temperature increases. The transformation of the F2 and F3+ centers is accelerated by action of laser radiation on γ-irradiated LiF crystals during annealing. [ABSTRACT FROM AUTHOR]

Concentration of band electrons and holes induced by multiphoton ionization in the filament of a femtosecond laser pulse with a diameter of 10 µm before and near the Gaussian waist in nonlinear crystals corresponds to 1018 − 1021 cm−3. Such level of the induced electron-hole polarization component makes an additional contribution to increasing the harmonic generation efficiency in the interaction of femtosecond radiation with nonlinear crystals. [ABSTRACT FROM AUTHOR]

This review analyzes theoretical calculations and laboratory experiments showing the prospects of using of diamond with color centers as active laser medium. Despite the mentioned prospects, practical implementation of lasers based on color centers in diamond is limited to laboratory demonstrations. No commercially significant products of laser technology based on diamond with color centers have been created yet. Obviously, the available scientific information is still insufficient, and additional research is required. The review analyzes the factors that require further study: concentration quenching of luminescence, thermal quenching of luminescence, luminescence quenching by nitrogen and other impurity defects, as well as the influence of multiphoton and multi-stage absorption processes. For color centers in diamond, such processes have yet to be investigated in more detail. [ABSTRACT FROM AUTHOR]

A review of the results studies on luminescence of mainly natural diamonds under X-ray excitation is presented. Such luminescence of diamond crystals is widely used in separation of diamond-bearing ores in diamond mining industry. Diamonds contain numerous luminescence centers that can be excited by optical radiation. Photoluminescence (PL) is characterized by wide variety of properties. It is difficult to discern PL of diamonds from PL of accompanying minerals and provide sufficient extraction selectivity. The first comparative studies of the properties of X-ray excited luminescence (XL) and photoluminescence, carried out in the last century, showed the properties of XL are much less diverse. X-ray luminescence spectra of most natural diamonds contain mainly one band, so-called A-band, visually perceived as blue emission. Spectral bands and lines observed in photoluminescence appear additionally in XL spectra of some samples. Some samples do not exhibit A-band in XL. The specific properties of XL of diamonds determined the capability of usage of XL in separation of diamond-bearing ores. In the mid-sixties, an idea stating the donor-acceptor process of emission of the A-band under X-ray excitation had appeared. This idea has been disputed on the basis of detailed study of kinetics and other properties of XL, but the concept of the donor-acceptor process has been circulating in various publications for several decades. The review presents the temperature dependences of the decay time constants of individual components of X-ray excited luminescence, which as a whole should be considered as the temperature-time passport of the A-band. The article provides data on the practical use of luminescence in the separation of diamond ores, provides some information on the design of separators. [ABSTRACT FROM AUTHOR]

This paper presents the results of studies of X-ray luminescence (XL) of zircons from three highly diamondiferous kimberlite pipes in Yakutia (Russia). Those zircons acquired the typical rounded shape as a result of ancient mechanical abrasion or dissolution. The photoluminescence (PL) color of zircons varies from blue-green to yellow-orange. The PL spectra contain from one to three structureless bands. The color saturation of samples depends on the source and increases in the sequence Mir – Udachnaya – Nyurbinskaya pipes. The system of peaks at 480 and 580 nm, characteristic of rare earth elements, were observed in all X-ray luminescence spectra. The relative intensity of luminescence of the 380 nm band in XL spectrum decreases with increasing color saturation and increases with the lightening of crystals during annealing. The intensity of the 450–650 nm band with a maximum at 540 nm changes slightly during annealing up to 500°C. Zircons are colored under influence of X-ray radiation – at least two types of absorbing defects (color centers) are formed, the concentration of the color centers linearly depends on the irradiation dose. The similarities and differences between zircons from the main industrial kimberlite diamond deposits of Yakutia are shown. [ABSTRACT FROM AUTHOR]

Color centers, found in lithium fluoride crystals grown in a reducing atmosphere and irradiated with a low dose of X-ray radiation, emit spectral luminescence band with maximum λmax = 800 nm and decay time constant of 26.5 ± 1 ns at room temperature. As the radiation dose increases, the concentration of these centers quickly saturates, while the concentrations of known intrinsic color centers continue to increase. This indicates the impurity nature of these color centers. The trajectories of the luminescence intensity and the decay time constants of single centers of this type were investigated. The luminescence is of flickering character. The temporal characteristics of the trajectories of luminescence intensity for different centers of the same type are different, while their decay time constants are the same. Similar pattern was revealed for the F2 color centers. These properties of single color centers in monocrystals are discussed. [ABSTRACT FROM AUTHOR]

The dielectric spectra of LaF3 crystals activated by rare-earth ions Eu2+, Sm2+, and Yb2+, gradually cooled from 300 to 240 K, were investigated. Obtained experimental data were compared with experimental data obtained previously by other authors. The reorientation activation energies for RE2+ dipoles in LaF3 are 0.49, 0.55, 0.56, and 0.58 eV for Ba2+, Sm2+, Eu2+, and Yb2+, respectively. A reorientation of fluorine vacancy is observed, across the F1 positions. [ABSTRACT FROM AUTHOR]

The formation of particles during ablation of single crystals of natural diamond by laser radiation with a wavelength of 213 nm was studied. As a result of ablation, diamond particles of two characteristic sizes are formed. The linear size of large particles was on the order of 1 µm, small particles – from 300–400 nm and less. The spectra and kinetics of luminescence of the original crystal and the resulting nanoparticles were recorded. Measurements showed that the spectra of nano- and microparticles are radically different from the spectra of the original single crystals. The luminescence of nanoparticles did not manifest the characteristic structure of spectra and the corresponding decay time constants of luminescence of N3 and H3 color centers observed in the original single crystals. Instead, a broad complex luminescence band with several different decay time constants was observed. It was found that this luminescence is caused by the products of graphitization of the surface of nano- and microparticles, as well as the surface of a crater formed on a diamond single crystal as a result of ablation. The absorption of optical radiation that excited luminescence in the experimental studies of particles and craters was so strong that the luminescence of the main diamond composition of nanoparticles and a diamond crystal under the graphitized layer was not detected in experiments. [ABSTRACT FROM AUTHOR]

The paper presents the results of luminescent studies of organs and tissues of endemic pelagic crustaceans during ontogenesis through the example of Epischura baikalensis. The spectral-kinetic characteristics of luminescence of E. baikalensis specimens have been measured. The results of laser confocal scanning luminescence microscopy studies with time resolution showed that the luminescence spectra of E. baikalensis is mainly defined by emission of Green Fluorescent Protein (GFP) and chlorophyll contained in cells of phytoplankton. [ABSTRACT FROM AUTHOR]

We present results of studies of formation mechanism of luminescence centers of the blue range in lithium fluoride crystals. We found that the centers under study are intrinsic defects of crystal lattice formed as a result of a radiation-thermal process in the temperature range much higher than room temperature. Experimental confirmation of simultaneous formation of these centers and F3+ centers, the increase in their concentration during thermal destruction of F3+ centers, and absence of the phonon structure characteristic of R2 centers give basis to attribute the considered centers to a stable configuration of intrinsic radiation defects constituting isomer of F3 center. [ABSTRACT FROM AUTHOR]

Characteristics of LiF crystals irradiated by pulsed laser radiation with pulse duration of 50 fs, an energy of about 5 mJ, and a wavelength of 950 nm were studied. After single-pulse irradiation, a band with maximum at wavelength of 450 nm related to formation of F3 color centers was observed in the extinction spectra of sample. With an increase in the number of pulses, components associated with more complex aggregate F3 (R), F3, and F4 (N) centers appear in the band structure. The observed association of F3+ centers leads to the formation of larger aggregates up to the precipitation of nanoscale lithium clusters, which is confirmed by comparison of spectra of the crystals irradiated with laser pulses and the crystals irradiated with high-energy Li+ ions with use of ion implanter. Atomic force microscopy study confirmed the conclusion that lithium nanoparticles with sizes in the range of 60–90 nm were formed in surface layer of LiF crystal as a result of laser irradiation. [ABSTRACT FROM AUTHOR]

Heating of relaxed band charge carriers occurs in ionic crystals under nanosecond irradiation by dense electron beam as a result of collisions of carriers with high-energy electrons during the action of excitation pulse. Heating of relaxed low-energy electrons in the conduction band (CB) in the process of multiphoton ionization of crystals is unlikely if the duration of excitation femtosecond laser pulses does not exceed the relaxation time of the induced high-energy electrons in CB. [ABSTRACT FROM AUTHOR]