Electrophysical properties of eutectic composites formed in the NaF-DyF3, NaF-HoF3, and MgF2-ScF3 systems are studied at 18–528°C. The conductivity of 25NaF-75DyF3, 25NaF-75HoF3, and 55MgF2-45ScF3 at 20°C (9 × 10−8, 3 × 10−7, and 2 × 10−6 S/cm) exceed that of the initial materials by 2–4 orders of magnitude.

Differential thermal analysis and X-ray powder diffraction were used to study phase diagrams for mixtures of NaF with La, Ce, Pr, Nd, and Sm trifluorides. Incongruently melting intermediate phases with the gagarinite structure and nonstoichiometric fluorite phases Na0.5-xR0.5+xF2+2x for R = Pr, Nd, or Sm, which are stable within narrow temperature ranges, were proven to exist. Solid solutions R1-yNayF3-2y with the tysonite structure, based on RF3, were discovered.

The effect of the variations in the elemental composition on the electrical conductivity of the material is studied for the Na0.5-x(R(1-y)Ry(y)*)(0.5 +x)F2+2x solid solutions (x = 0.08-0.11, y = 0.002-0.100) in which the pairs of rare earth elements (R, R*) are (Y, Nd), (Y, Yb), (Lu, Nd), (Lu, Ho), (Lu, Y), and (Lu, Tm). The conductivity was measured on single crystals grown from melt by the Bridgman-Stockbarger method in a fluorinating atmosphere. The anionic conductivity of the ternary Na0.5-x(R1-yRy*)(0.5+x)F2+2x solid solutions is almost the same as the conductivity of the binary Na0.5-xR0.5+xF2+2x solid solutions. This is explained by the fact that in the transition from binary to ternary crystals, the concentration of mobile fluoride anions remains unchanged (4.5% of the total number of fluoride anions), whereas the enthalpy of conductivity (characterizing the potential barriers on the path of the fluoride-ion migration) changes only insignificantly.

The ionic conductivity and permittivity of BaR2F8 (R=rare earth element) single crystals with monoclinic BaTm2F8 structure (space group C2/m) were measured in the temperature range from 300 to 700 K. A pronounced anisotropy of ionic conductivity and a slight anisotropy of permittivity are found. The fastest ionic transport with the lowest activation energy (∼0.56 eV) and the highest value of the permittivity are observed along the a axis. The minimum values of conductivity with the activation energy of 0.75–0.8 eV are observed along the c axis (e.g. the axis normal to the cleavage plane). The mechanism of the ionic transport in BaTm2F8 structure is discussed.

Multicomponent single crystals of monoclinic rare-earth fluorides were grown by the Stockbarger-Bridgman method from flux of the initial composition Ba(Er0.945Tm0.05Ho0.005)(2)F-8. The macrodistributions of Ba, Er, and Tm along the central and lateral parts of the single crystals were studied by the method of X-ray spectral analysis using a scanning electron probe. The uniform distributions of the components in the central part of the crystal and the nonuniform distributions in the peripheral part are explained by effect of the radial temperature gradient on the axial temperature gradient, which is considered as the parameter determining the macroperiodic homogeneity of the crystal composition.

The anisotropy of the ionic conductivity and permittivity of (1) BaR2F8 (R=rare earth element) single crystals with monoclinic BaTm2F8 structure and of (2) (β-YF3 structured) rare earth trifluorides is studied. Single crystals, eutectic composites and ceramics are investigated in a broad temperature range. In the monoclinic BaR2F8 crystals, a pronounced anisotropy of the ionic conductivity and a slight anisotropy of the permittivity are found. The fastest ionic transport with the lowest activation energy (0.563 eV) and the highest value of the permittivity are observed along thea axis. The temperature dependencies of the fluoride ion conductivities of various orthorhombic rare earth trifluorides differ only slightly from one another. For the bulky single crystals, the conductivity at 500 °C and the conduction activation enthalpy are equal to 1.1(4)×10−5 S/cm and 0.75(3) eV, respectively. The ionic conductivity is almost isotropic, but the anisotropy of the permittivity is significant. For the fluorides of both structural types, plausible conduction mechanisms are proposed, networks of most probable conduction paths are presented and the origin of the observed anisotropy of the ionic conductivity is elucidated.

Spectral studies of nonstoichiometric multicomponent fluoride crystals, doped with the Pr3+ ions, which have a CaF2-type partially disordered structure have shown that these crystals are promising candidates for amplifiers in the 1.3 μm range. In Ba1−xRxF2+x:Pr crystals the oscillator strengths of all transitions are markedly increased in comparison with those in BaF2 crystals due to the formation of centres with a low symmetry of their local environment. The concentration quenching of the luminescence in Ba1−xRxF2+x:Pr and Pb0.67Cd0.33F2:Pr crystals as well as the probability of nonradiative relaxation from the 1G4 state are smaller than those in glasses.

The spectroscopic properties of Pr3+ doped nonstoichiometric fluoride crystals with CaF2 type of structure sensitized by Yb3+ ions have been studied. It is a promising medium for 1.3 μm optical amplifiers. The comparison of line strengths calculated using the modified Judd-Ofelt and Kornienko et al. theories shows that a better agreement between experimental and calculated data is given by the latter theory. Using the experimental data on efficiency of energy transfer Yb→Pr optimal concentrations of the Pr3+ and Yb3+ ions and single pass gain coefficients have been calculated.

Optical properties with more than 120 multicomponent nonstoichiometric fluoride crystals M+,2+Fm-R3+Fn with CaF2 structure doped with Nd3+ and Pr3+ were studied especially in 1.3 micrometers spectral range which is promising for operation in the second telecommunication window. The direct measurements of excited state absorption and single pass gain in 1.3 micrometers range have been carried out for Na0.4Y0.6F2.2 and Ca0.9Y0.1F2.1 crystals. The effective cross-sections and halfwidth of gain band have been determined ((sigma) max equals 2.2 +/- 0.7 10-21 cm2, (Delta) equals 40 cm-1 and (sigma) max equals 4.5 +/- 0.9 10-21 cm2, (delta) equals 60 cm-1, respectively). The line's strengths in Ba1-xGdxF2+x:Pr crystals has been found to be raised in nonstoichiometric crystals in comparison with stoichiometric ones due to formation of another type of optical centers. The energy of destruction of these Pr3+ positions has been determined to be 280 cm-1. The mean decay rate of Yb3+ is found to be proportional to the multiplying of Yb3+ and Pr3+ concentrations in Yb3+ sensibilized BaGdF:Yb,Pr and PbCdF:Yb,Pr crystals. The optimal concentrations of Yb and Pr and single pass gain coefficient have been calculated.

Investigations of luminescence and radiation characteristics of a series of heavy crystals based on CdF2, BaF2, LaF3, Pb0.67Cd0.33F2, Na0.4Yb0.6F2.2, and Y3Al5O12, and a Phi-113 lead glass are presented. The radiation resistance of crystals based on CdF2 doped with YbF3, BiF3, and InF3 is more than 10 Mrad. We have also discovered that the relative light yield of Cd0.95Mn0.05F2 is similar to 20000 photon/MeV, its basic luminescence decay time is similar to 300 mu sec, and the luminescence spectrum has a maximum at about 550 nm.

The spectroscopic characteristics in the 1.3 mum region of nonstoichiometric fluorite phases M1-xRxFm(1-x)+nx, doped by Nd3+ ions were investigated. The direct measurements of excited state absorption and amplification in 1.3 mum region were carried out. The halfwidth of amplification spectrum in Na0.5-xY0.5+xF2+2x and Ca1-xYxF2+x crystals was found to be less than that the halfwidth of the luminescence spectrum due to excited state absorption (ESA). The maxima of amplification bands are located at approximately 1365 nm with halfwidth of approximately 40 nm for Na0.5-xY0.5+xF2+2x crystals and approximately 60 nm for Ca0.9Y0.1F2.11 crystals. The maximum values of effective cross sections sigma(eff) = sigma(em) - sigma(esa) for these crystals are 2.2 +/- 0.7 x 10(-21) cm2 and 4.5 +/- 0.9 x 10(21) cm2, respectively.