The correct conditions for measuring the luminescence intensities in fi laments formed by the action of femtosecond laser pulses were found for lithium fluoride crystals. The determined conditions ensured that the measured intensities were proportional to the concentrations of luminescent color centers created in the crystals by the laser radiation and allowed conclusions to be drawn about the processes occurring in the filaments. Near-cluster color centers were found, indicating the presence of nanosized clusters in all areas of the fi laments.

The photoluminescence of lithium fluoride nanocrystals and crystals placed on the anode of an atmospheric-pressure glow discharge in helium and exposed to the discharge components was studied. The luminescence spectra showed that color centers with new properties inherent to near-cluster centers were formed in unannealed nanocrystals after exposure to the discharge. However, the conditions necessary for formation of near-cluster centers were eliminated upon annealing of the nanocrystals. These necessary conditions were partially restored when annealed nanocrystals were exposed to the discharge. This opened new possibilities for elucidating the processes and mechanisms of formation of centers with new properties.

Thermoluminescence spectra in the temperature range 80–300 K were compared for lithium fluoride nanocrystals and crystals. Four and one band were observed in the spectra of nanocrystals and crystals, respectively. Thermoluminescence intensities integrated over the spectrum and temperature range were measured for two types of lithium fluoride samples in one of which radiation color centers with new properties could form and in the other of which they could not form. The intensity was found to be significantly higher in samples of the first type.

Brief review of the data on the color centers, which are formed in the near-cluster regions of LiF, NaF and MgF2 nanocrystals, is presented in this paper. The wavelengths of the maxima and half widths of the absorption and photoluminescence bands, photoluminescence lifetimes, the values of the Huang-Rhys parameters, the wavelengths of zero-phonon lines for the bulk and near-cluster color centers in LiF, NaF and MgF2 are given.

It has been established that in lithium fluoride crystals, subjected to pre-irradiation thermal shocks or compression, intrinsic point defects with new properties different from the known properties of the usual defects of the same composition are formed as a result of irradiation. The obtained new properties are similar to those for radiation-induced defects that were previously registered in nanocrystals and called near-cluster defects. It is shown that the combination of pre-irradiation heating and compression of a crystal increases the ratio of the concentrations of formed near-cluster and usual defects.

It is shown that the ratio of concentrations of near-cluster and conventional radiation color centers increases in magnesium fluoride nanocrystals in the case when the manufactured samples before irradiation are kept for some time at a temperature higher than the anion vacancies mobility temperature. Such preirradiation heat exposure on lithium fluoride nanocrystals leads to the formation of near-cluster aggregation color centers during radiation exposure of the samples. It is established that differences in pre-irradiation thermal effects on the samples affect the kinetic of concentration growth of aggregate near-cluster centers in the post-radiation period. Conclusions are made about the mechanism and processes of nanoclusters formation in the samples, as well as about the defects involved in the formation.

The luminescence and absorption properties of LiF, NaF and MgF2 nanocrystals containing radiation-induced point defects with new properties are investigated. The influence of temperature, at which nanocrystals are maintained after their manufacture, on the efficiency and kinetics of such defects formation is examined. For LiF samples, the activation energy of fotmation processes is determined. X-ray diffraction reflections are compared for LiF nanocrystals, unannealed and annealed after fabrication, unannealed and irradiated with γ-rays or electrons, as well as those manufactured by fragmentation of an irradiated crystal plate. Conclusions are drawn about the processes of self-assembled nanostructures formation, the presence of which is a prerequisite for the creation of radiation-induced point defects with new properties.

The ratio of concentrations of nearcluster and conventional color centers increases in magnesium fluoride nanocrystals when prepared samples are maintained for some time before irradiation at a temperature higher than the temperature for mobility of the anion vacancies. Such pre-irradiation treatment of lithium fluoride nanocrystals leads to the formation of near-cluster aggregation of color centers during radiation exposure of the samples. Differences in the preirradiation temperature regimes of the samples affect the kinetics of the growth of the concentration of aggregate nearcluster centers in the post-radiation period. Conclusions are drawn concerning the mechanism and processes of nanocluster formation in the samples as well as the defects involved in their formation.

The formation features of the single-frequency unidirectional monopulse lasing mode of a Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump with injection of external narrow-band optical radiation into the cavity are studied. The asymmetric layout of the intracavity elements relative to the output mirror and depolarization effects in them cause the energy and polarization of the monopulse Nd:YAG ring laser to differ depending on the input direction (clockwise or counterclockwise) of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is most evident for a change from active to passive Q-switching.

The formation features of the regime of single-frequency unidirectional monopulse lasing of Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump under the condition of injection of external narrow-band optical radiation into the resonator are studied. It is experimentally shown that the asymmetrical layout of the intracavity elements relative to the laser output mirror and the depolarization effects in these elements lead to a difference in the energy and polarization of the monopulse Nd:YAG ring laser depending on the direction (clockwise or anticlockwise) of the input of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is the most evident in the case of transition from the active to the passive Q-switching.

Changes in the concentrations of ordinary radiation defects and formation of near-cluster radiation defects (color centers) are shown to occur in nanocrystals fabricated by mechanical fragmentation of irradiated LiF crystals. Concentrations of near-cluster color centers increase to a steady value after fragmentation and remain constant at room temperature for a long time. UV irradiation of fabricated nanocrystals after termination of center formation processes in them causes the concentration of near-cluster defects containing three anion vacancies and two electrons to increase significantly. It is demonstrated that there are single-vacancy color centers as well as ordinary and near-cluster aggregate centers in unirradiated nanocrystals fabricated by fragmentation of unirradiated crystals.

Nanocrystals of magnesium fluoride have been irradiated by gamma-rays at 77 K or electrons at room temperature. Three types of radiation-induced defects (color centers) with previously unknown characteristics, such as luminescence and excitation luminescence spectra, luminescence lifetime, and Huang-Rhys parameters, have been observed and studied in these nanocrystals. It has been established that the luminescence excitation spectra of these centers contain two closely spaced bands with slightly different intensities. It was shown that pre-irradiation annealing of nanocrystals at temperatures above 823 K for one hour leads to the impossibility of observing all three new types defects in irradiated samples. It has been found that during the post-radiation annealing of samples, one of the new types of color centers is transformed into a well-known defect described earlier in the literature. It is concluded that new types of defects are generated near the nanoclusters which are formed during nanocrystals production. It has been found that defects previously known and referred to as M (C-1) consist of two modifications which differ in luminescence and excitation luminescence spectra, and in dependencies of their concentrations upon temperature annealing.

The possibility of formation of radiation defects with new luminescent properties is investigated in sodium and magnesium fluorides nanosized crystals. Nanocrystals obtained by mechanical fragmentation of the single crystals have been irradiated by gamma-rays at 77 K or electron beams at room temperature. Their TEM images have been received. Luminescence, luminescence excitation and absorption spectra of nanocrystals have been measured immediately after.-irradiation without samples defrosting and after termination of the defects aggregation processes at room temperature. The formation of radiation color centers with previously unknown optical characteristics has been discovered in nanocrystals. Numbers of anion vacancies and electrons entering into these centers composition were established in sodium fluoride. The structure transformation of the centers, containing two anion vacancies and an electron, was revealed after sodium fluoride samples defrosting. For sodium fluoride the data on the Huang-Rhys parameters and lifetimes of the photoluminescence for here studied and previously known centers of the same composition are determined and compared. The results obtained show that near-clusters color centers can be formed in crystals with different structures and atomic compositions.

Near-surface color centers in sodium fluoride nanocrystals have been formed. At pre-irradiation annealing of sodium and lithium fluorides samples at temperatures of 623 K and above, the near-surface color centers in them have not been found after gamma-irradiation. Annealing lithium fluoride nanocrystals with the near-surface defects leads to their transformation into bulk ones of the same composition.

It is shown that surface color centers of the same type are formed in the surface layer and in regions with damaged crystal structure inside crystalline lithium fluoride after γ-irradiation. Results are presented from a study of the effect of pre-irradiation annealing on the efficiency with which surface centers are formed in lithium fluoride nanocrystals. Raising the temperature for pre-irradiation annealing from room temperature to 250°C leads to a substantial reduction in the efficiency with which these centers are created. Surface color centers are not detected after γ-irradiation for pre-irradiation annealing temperatures of 300°C and above. Adsorption of atmospheric gases on the crystal surface cannot be regarded as a necessary condition for the formation of radiation-induced surface centers.

A Q-switched Nd : YAG laser with a high-power transverse diode pumping and injection of seed radiation generated by a single-frequency semiconductor laser is described. The threshold seed radiation power at which the Q-switched Nd : YAG switches to the single-frequency mode is 0.44 mW (radiation intensity 5.6 x 10(-2) W cm(-2)). With increasing injection power, the spectral and power characteristics of the Q-switched laser almost do not change at a constant excitation of its active medium. The spectral linewidth of the Q-switched Nd : YAG laser with injection from a TLD-1060-14BF single-frequency semiconductor laser module does not exceed 90 MHz (wavelength 1064 nm).

The features of forming output radiation in a powerful monopulse single-frequency side diode-pumped laser operating in external narrow-band signal seeding mode were investigated. The monopulse single-frequency laser was fabricated of a YAG:Nd active element excited by three laser diode matrices. A compact continuous-wave YAG:Nd-laser with longitudinal diode pumping served as the seeding laser. It was shown experimentally that the transition of the monopulse laser from multimode to single-frequency lasing with a spectral line width of about 54 MHz (0.2 pm) occurs at seeding-laser radiation power P th ≈ 0.14 mW (radiation intensity of 1.8·10 –2 W/cm 2 ). Increasing the seeding-laser power over P th does not lead to a noticeable change of the output characteristics of the monopulse laser for a given pump level (above the threshold). If the pump power varies from 1.5 to 3.0 kW, the P th value is not changed but the energy of the output pulses of single-frequency monopulse generation increases to 40 MJ. The low level of the external narrow-band seeding signal allows us to consider the single-frequency low-power semiconductor laser as a promising source of the seeding signal.

Lithium fluoride nanocrystals were irradiated by gamma rays at a temperature below the temperature corresponding to the mobility of anion vacancies. The kinetics of the aggregation of radiation-induced defects in subsurface layers of nanocrystals during annealing after irradiation was elucidated. The processes that could be used to determine the activation energy of the diffusion of anion vacancies were revealed. The value of this energy in subsurface layers was obtained. For subsurface layers, the concentrations ratio of vacancies and defects consisting of one vacancy and two electrons was found. The factors responsible for the differences in the values of the activation energies and concentration ratios in subsurface layers and in the bulk of the crystals were discussed.

Eight nominally pure lithium fluoride crystals, obtained from a single LiF crystal containing less than 100 ppm impurities, were irradiated by gamma-rays from a Co-60 source at room temperature, with doses from 8.4 to 2.5 x 10(5) Gy, but one at -60 degrees C. Optical density measurements were performed to investigate the radiation-induced color centres (CCs) and to evaluate their concentrations. Thermoluminescence (TL) glow curves were collected and simulated by a first-order kinetics approach, and from the best-fit procedure ten glow peaks (GPs) spanning from 100 to 450 degrees C were highlighted. A comparative analysis of GP intensities and CC concentrations as a function of the irradiation dose has questioned their association as obtained in previous measurements, showing the impurities, less than 10(18) cm(-3), still playing a predominant role in TL spectra. New measurements on LiF crystals more pure, at least an order of magnitude, are required to establish for sure the association of GPs to CCs.

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.