Yu. V. Orlov

Interaction of Pr3+ optical centers in the Y2SiO5 crystal

It is shown on the basis of studies of the optical spectra and luminescence decay of nonequivalent Pr3+ optical centers in the Y2SiO5 crystal that the occupation of the nonequivalent cation sites of the crystal lattice by the activator ions is irregular. For excitation in the region of the optical transitions 3H4→1D2in the temperature interval 6–80 K there is no transfer of electronic excitation energy between Pr3+ ions localized in different cation sites. The luminescence decay law of the Pr3+ optical centers is determined by the concentration of activator ions and has a complicated non-single-exponential character; the quenching of the luminescence of the Pr3+ ions is due to the formation of dimers of these ions.

Spiky structure of coherent emission from optically thick media

The spiky structure of the spontaneous emission from praseodymium ions in the LaF3 lattice on the 3P0-3H6 transition under coherent pulsed excitation of the adjacent 3H4-3P0 transition has been studied experimentally and theoretically. The experimental results are in good agreement with the theoretical conclusions based on analysis of the emission dynamics of an excited ensemble of three-level systems in the mean field approximation. The generation of a spiky structure is interpreted as the emission of a cnoidal wave pulse. The recorded random pattern of time intervals between the spikes reflects the sensitivity of the cnoidal wave period to fluctuations in the system. The developed theory has been found to be related to models of deterministic chaotic dynamics.

Manifestation of quasi-symmetry of the cation sites of Gd2SiO5, Y2SiO5, and Lu2SiO5 in the spectra of the impurity ion Pr3+

The quasi-symmetry of the inequivalent cation sites in the crystals Gd2SiO5, Y2SiO5, and Lu2SiO5 is established on the basis of an analysis of the features of the low-temperature optical spectra of the impurity ion Pr3+. One type of cation site of the crystals Y2SiO5 and Lu2SiO5 manifests the quasi-symmetry of a distorted octahedron, and the other type, that of a distorted tetrahedron. The parameters characterizing the energy spectrum of the free Pr3+ ion in the crystalline field of the cation sites are determined.

The nature of activation centers in Y2SiO5:Pr3+, Gd2SiO5:Pr3+, and Lu2SiO5:Pr3+ crystals

A complex study of the energy spectra and relaxation channels for the excitation energy of activation centers in Y2SiO5:Pr3+, Lu2SiO5:Pr3+, and Gd2SiO5:Pr3+ was performed. An analysis of the low-temperature optical spectra showed that the energy parameters and the character of field splitting of the 1D2 and 3H4 activator ion terms were substantially different in crystals of different crystallographic types. The pseudosymmetry effect was observed in splitting of the 1D2 and 3H4 terms of Pr3+ ions situated in nonequivalent crystal lattice cation sites of Y2SiO5 and Lu2SiO5. Activator ions nonuniformly populated nonequivalent cation sites of the Y2SiO5 crystal lattice. At high activator ion concentrations (>1 at %), luminescence decay in Y2SiO5 could not be described by a simple exponential time dependence. The complex luminescence decay law was caused by activator ion excitation energy migration and capture by acceptors. The role of energy acceptors was played by activator ion dimers.

Superradiant emission of LaF3:Pr3+ in resonator

Experimental data concerning superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented in the cases of a free medium and when the medium is placed into an optical resonator. The spike structure of superradiance is registered and studied. When the medium is placed inside a cavity, a new channel of energy removal by superradiance related to the cavity mode appears; the old noncavity channels are preserved. The duration of superradiance in the cavity channel is decreased, and regular modulation arises. These peculiarities of superradiance induced by the presence of an optical resonator are explained.

Selective spectroscopy of Pr3+ impurity ions in Y2SiO5, Gd2SiO5, and Lu2SiO5 crystals

Based on a study of the low-temperature optical spectra of Pr3+ activator ions in Y2SiO5, Gd2SiO5, and Lu2SiO5 crystals, it is shown that the parameters and character of the crystal-field splitting of the 1D2 and 3H4 terms of the impurity ions are substantially different in crystals belonging to different crystallographic types. In Y2SiO5 and Lu2SiO5 crystals a pseudosymmetry effect is observed in the splitting of the 1D2 term for ions localized in inequivalent cation sites. The activator ions nonuniformly occupy the inequivalent cation sites as their concentration is increased. At high concentrations of activator ions (∼1 at. %) the optical absorption spectra exhibit spectral lines belonging to dimers of activator ions.

Anomalies in the concentration quenching of luminescence in doped Y2SiO5:Pr3+ nanocrystals

In Y2SiO5:Pr3+ nanocrystals, an ordered phase is observed in the 1D2 luminescence decay curves of Pr3+ ions at their anomalously low concentration (0.5 at %). This effect is caused by the predominant accumulation of activator ions near the nanocrystal surface, which provides relaxation of the elastic strains arising as a result of the misfit between the ionic radii of Pr3+ and Y3+. The concentration quenching of Pr3+ luminescence is due to cooperative cross relaxation.

Temporal structure of superradiance of praseodymium ions in the LaF3 matrix: theory and experiment

Experimental data and theoretical model describing stochastic pulsations within oscillatory mode of superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented. The model deals with three-level system with close upper levels and reflects our experimental data on fluorescence of praseodymium ions. The mean-field approximation is used to develop the superradiance theory. In determined case basic equations of the developed model are reduced to well known Lorenz equations of deterministic chaotic dynamics.

Dynamics of superradiant medium in resonator

Experimental data and theoretical model concerning superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented in cases of free medium and when the medium is placed into resonator. The spiky structure of superradiance is registered and studied. When the medium is placed inside a cavity, a new channel of energy removal by superradiance related to the cavity mode appears; the old noncavity channels are preserved. The duration of superradiance in each channel is decreased and the modulation arises. These peculiarities of superradiance induced by the presence of resonator are explained on the basis of the developed mean-field theory.

The features of coherent stimulated emission of Pr3+ doped into LaF3 matrix

The paper presents the experimental results on temporal characteristics of coherent stimulated emission on the 3PO-3H6 transition of Pr3+ doped into the LaF3 matrix while turning the pumping frequency in the vicinity of 3H4-3PO transition. The stimulated emission was generated in the modes both with and without an external resonator. It was found that the emission duration could be up to 2 μs and consisted of train of spikes. Simultaneously the fluorescence emission was observed on the 3PO-3H4, 3H5j, 3H6, 3F2 transitions Pr3+, which also had a complicated temporal form.