[en] One investigated both experimentally and theoretically into spike structure of spontaneous radiation of praseodymium ions in LaF₃ matrix at ³P₀-³H₆ transition frequency under coherent pulse excitation of ³H₄-³P₀ contact transition. The experimental results are in line with the theoretical calculations based on the analysis of radiation dynamics of the excited group of three-level systems in the mean field approximation. The spike structure generation is interpreted as a cnoidal wave pulse radiation. The recorded random nature of time intervals between spikes reflects sensitivity of cnoidal wave period to fluctuations within the system. One revealed the relation of the elaborated theory with determinate chaotic dynamics models

[en] Based in the analysis of absorption and luminescence spectra of Y₂ Si O₅ crystals the existence of two Pr³⁺ optical centers associated with the location of doped ions in nonequivalent cation sites is proved. A nonradioactive excitation energy transfer between the nonequivalent Pr³⁺ optical centers is observed. Preliminary analysis of the transfer mechanisms is made

[en] The investigation of low-temperature optical spectra of Pr³+ activator ions in Y₂SiO₅, Gd₂SiO₅, Lu₂SiO₅ crystals shows that the parameters and the character of crystalline splitting od ¹D₂ and ³H₄ terms of the impurity ions are essentially different for crystals of different crystallography types. On splitting of the ¹D₂ term Y₂SiO₅ and Lu₂SiO₅ crystals display an effect of pseudo symmetry for ions localized in nonequivalent cation sites. As the concentration of the activator ions is increased they occupy the nonequivalent cation sites non uniformly. At high concentrations of the activator ions (approx 1 at.%) the optical absorption spectra exhibit spectral lines responsible for their dimers

[en] Paper presents results of comprehensive investigation into energy spectrum and relaxation channel of excitation energy of activation centres in Y₂SiO₅:Pr³⁺, Gd₂SiO₅:Pr³⁺ and Lu₂SiO₅:Pr³⁺ crystals. Analysis of low-temperature optical spectra shows that energy parameters and nature of field splitting of ¹D₂ and ³H₄ therms of activator ions differ essentially for crystals belonging to different crystallographic types. In Y₂SiO₅ and Lu₂SiO₅ crystals one observes effect of pseudosymmetry at splitting of ¹D₂ and ³H₄ therms of Pr³⁺ ions localized in nonequivalent cation nodes of crystalline lattice. Activator ions populate irregularly nonequivalent cation nodes of Y₂SiO₅ crystalline lattice. At high concentrations of activator ions (> 1 at. %) in Y₂SiO₅ crystal dying down of luminescence is not described by simple exponential time dependence. Complex law of luminescence dying down results from migration and capture of activator ions in excitation energy acceptors. Dimers of activator ions are the energy acceptors

[en] Based on the analysis of the low-temperature optical spectra of the Pr³⁺ impurity ion, the quasisymmetry of nonequivalent cation sites in Gd₂SiO₅, Y₂SiO₅, and Lu₂SiO₅ crystals is determined. The type of the cation sites in Y₂SiO₅ and Lu₂SiO₅ displays a quasi-symmetry of distorted octahedron and the other one exhibits a quasi-symmetry of distorted tetrahedron. The parameters characterizing the energy spectrum of the free Pr³⁺ ion and the crystalline field of the cation sites are obtained