Photoluminescence properties of core-shell SiO2/Lu2O3: Eu monodisperse heteronanoparticles

Core-shell monodisperse heteroparticles of the composition SiO₂/Lu_1.86Eu_0.14O₃ have been synthesized using the developed technique for preparing spherical colloidal silicon dioxide particles with the size dispersion in the range 2.0–2.5% and the procedure for producing nanocoatings on the surface of spheres by codeposition. The structure of heteroparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions has been examined. It has been revealed that the luminescence decay time for heteroparticles increases by a factor of approximately two compared to that for a powdered luminophor Lu₂O₃: Eu (7 at %) prepared and treated under the same temperature conditions as the SiO₂/Lu₂O₃: Eu (7 at %) heteroparticles. This effect has been attributed to the change in the effective refractive index and the local density of photon states in luminophor nanolayers of heteroparticles.     

Biphoton light with hidden polarization and its polarization tomography

Polarization properties of biphoton light, emitted by an optical parametric oscillator, are studied both theoretically and experimentally. The theoretical treatment is performed using the Stokes operator formalism; polarization density matrix of the light fields; and the quasi-probability function, which represents an analog of the field Wigner function. The hidden polarization of biphoton light is demonstrated experimentally with the help of elements of polarization tomography.     

Determination of spectral width and chirp of ultrashort light pulses by analysis of second harmonic beam divergence

It is shown that in the noncollinear second harmonic generation scheme used for ultrashort light pulse duration measurements the divergence of the second harmonic beam is determined by the spectral width and chirp of the pulse. This enables one to measure simultaneously the spectral width, pulse duration, spectral-time product, chirp and its sign for a single pulse in the same device.     

Measurement of relaxation times by phase-modulated ultrashort light pulses

In the measurement of relaxation times of nonlinear response of media by means of ultrashort light pulses the resolution time is determined by the pulse duration. Here we show that using phase-modulated pulses the resolution can be as high as the coherence time $\text{τ}{}_{\mathrm{c}}\text{≈}\text{1}\text{Δν}$ (Δν is the width of pulse spectrum in Hz) which is less than the pulse duration.     

Liquid-metal field electron source based on porous GaP

We have reported on a new method for obtaining a liquid-metal field emitter. The treatment of a porous crystal of GaP binary semiconducting compound with high-voltage pulses in a vacuum has made it possible to obtain stable structures on its surface in the form of discrete gallium clusters. These structures exhibit high emission properties, including stable currents at a level of a few microamperes, as well as the high uniformity of the distribution of emission nanocenters over the surface.

     

Growth of faces of K2Co x Ni1 – x(SO4)2 · 6H2O mixed crystals

Data on the morphology and normal growth rate of the (110) and (001) faces, velocities of step motion, and slopes of dislocation hillocks on the (001) face of K₂Co _x Ni₁– _x (SO₄)₂ · 6H₂O crystals at different supersaturations of solutions with a Co/Ni ratio equal to 1: 1 or 1: 2 have been obtained using a Michelson interferometer. The morphology of the (110) faces is found to be the same for solutions of both compositions. Powerful dislocation sources with large Burgers vectors dominate on the (001) face. The morphology of the (001) surface is rougher than that of (110), especially in a 1: 2 solution at high supersaturation. The (110) faces grow more slowly as compared with (001). The kinetic coefficients of steps on the (001) face are identical in the 1: 1 and 1: 2 solutions. The influence of the kinetic and morphological characteristics of (001) faces on the single-crystal quality is analyzed.

     

Structural modification of synthetic opals during thermal treatment

The density and porosity of synthetic opals with spheres 315 and 1000 nm in diameter were measured in relation to the annealing temperature. At annealing temperatures of up to 500°C, the seeming density and porosity remain almost unchanged. Then, at temperatures of up to 950°C, the density increases gradually and, accordingly, the porosity decreases due to the collapse of nanopores caused by the sphere substructure. As the annealing temperature increases further, the opal density increases sharply up to 2.22 g/cm³ (which corresponds to the density of amorphous silica) and the open microporosity due to the voids between spheres disappears. Differential thermal and thermogravimetric analyses showed that SiO₂ powders with particles with average size of 315 and 1000 nm can have, respectively, two-and three-level systems of micro-and nanopores.     

Dispersion of light in opal photonic crystal

The selective reflection spectra of films prepared from the photonic crystal, i.e., synthetic opal, are investigated. It is revealed that the refractive index changes at the boundaries of the photonic band gap. The wave vector is renormalized as a result of the interaction of the light wave with the periodic structure of the crystal, and the dependence of the frequency on the photon wave vector deviates from a linear behavior. The band gap determined from these data is approximately equal to 1.7 × 10¹⁴ Hz.     

Growth and magneto-optical properties of Na0.37Tb0.63F2.26 cubic single crystal

Crystals of Na_0.37Tb_0.63F_2.26 solid solution with a fluorite structure have been grown from melt by the Bridgman technique. The measured values of the Verdet constant are V = 0.35 ± 0.02 and 0.105 ± 0.01 arcmin/(Oe cm) for λ = 633 and 1060 nm, respectively. The dispersion of the Verdet constant is studied in the range of 380–1060 nm. The Na_0.37Tb_0.63F_2.26 crystal is somewhat inferior to the previously studied noncubic fluoride crystals containing Tb³⁺ ions yields by V(λ) and is close to KTb₃F₁₀ crystal in totality of properties.