V. M. Masalov

Manipulating emission of CdTeSe nanocrystals embedded in three-dimensional photonic crystals

We report experimental and theoretical results on the photoluminescence of CdTeSe nanocrystals, embedded in a silica opaline structure by infiltration of a highly diluted solution. Strong modification of emission diagrams of embedded nanocrystals have been observed in good agreement with theoretical models. At macroscopic scale, we measured the difference of nanocrystals emission lifetime embedded either in an opal for which the emission is in the gap, or in an opal of smaller balls diameter for which the emission is outside the gap. The photonic bandgap effect leads to a lifetime increase of the order of 10%. These lifetime variations are shown to be in good agreement with the calculated local density of states modification due to the pseudogap.

Porous structure of synthetic opals

Some adsorption, structural, and annihilation characteristics of synthetic opals are measured. An analysis of these characteristics makes it possible to conclude that the total porosity in opals comprises macropores, which are in essence the voids between structure-forming spheres, and nanopores connected to the substructure of the spheres. The systems of macropores and nanopores are separated by narrow channels that collapse upon the thermal treatment of opals. The sizes of primary a-SiO2 particles and nanopores, which correspond to the voids between these particles, are estimated.

The Intrinsic Structure of Spherical Particles of Opal

The intrinsic structure of spherical SiO2 particles synthesized by hydrolysis of tetraethyl orthosilicate in an alcohol-water-ammonia medium was studied using transmission electron microscopy. It was established that the relatively large spherical silica particles were “tertiary” structures made up of smaller spherical particles (“ secondary” particles), which in turn consisted of even smaller primary spherical particles 5–10 nm in diameter. It was shown that, under the experimental conditions, the large SiO2 particles can contain a central core comprising primary particles surrounded by several layers of secondary particles smaller than the core diameter.

Photoluminescence of ZnO layers grown on opals by chemical deposition from zinc nitrate solution

The emission from ZnO layers grown on the surface of bulk opals using chemical deposition is studied under excitation by the 351.1 nm line of an Ar+ laser at different excitation power densities and temperatures. The emission spectrum exhibits narrow photoluminescence (PL) bands associated with the recombination of bound and free excitons as well a relatively broad band around 3.31 eV. The width of the excitonic lines (2–3 meV) along with their energy position are indicative of the high quality and strain-free state of the layer. The origin of the 3.31 eV PL band is discussed in connection with its dependence upon the excitation power density and temperature.

Colloidal particles of silicon dioxide for the formation of opal-like structures

The conditions of synthesis of silicon dioxide particles with a high degree of monodispersity have been investigated. The particles have been synthesized using both the hydrolysis of tetraethoxysilane in the presence of L-arginine and a combination of this technique with the traditional Stöber method. It has been shown that the use of SiO2 particles synthesized by the heterogeneous hydrolysis of tetraethoxysilane in the presence of the amino acid for their further growth according to the Stöber method makes it possible to obtain particles 100 nm and more in size with a narrow size distribution (the deviation of the diameter is less than 3%), a nearly perfect spherical shape, and a smooth surface.

Adsorption of lanthanides(III), uranium(VI) and thorium(IV) from nitric acid solutions by carbon inverse opals modified with tetraphenylmethylenediphospine dioxide

Carbon inverse opals (C-IOP) were noncovalently modified with tetraphenylmethylenediphospine dioxide (TPMDPDO). The distribution of TPMDPDO between C-IOP and aqueous HNO3 solutions has been studied. The effect of HNO3 concentration in the aqueous phase and that of the TPMDPDO concentration in the sorbent phase on the adsorption of microquantities of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, U, and Th nitrates from HNO3 solutions by C-IOP modified with TPMDPDO is considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanide(III) adsorption from moderate-concentration HNO3 solutions decreases with increasing element atomic number.

Luminescent properties of synthetic opal

We have studied the effect of the photonic band gap on the visible luminescence of opal photonic crystals. The results indicate that the position of the photonic band gap in the luminescence and reflection spectra of opal depends on the photon propagation direction. Optical measurements have been used to determine the refractive index of opal and the diameter of silica spheres. We have assessed the effect of oxygen annealing on the intrinsic luminescence spectra and crystal structure of opal. The emission centers in synthetic opal have been tentatively identified. The visible luminescence intensity in opal is shown to be anisotropic, in accordance with the frequency and angular dispersions of the first photonic band gap in opal.

A novel sorbent for lanthanide adsorption based on tetraoctyldiglycolamide, modified carbon inverse opals

Carbon inverse opals (C-IOP) were noncovalently modified with tetraoctyldiglycolamide (TODGA). The effect of HNO3 concentration in the aqueous phase and that of the TODGA concentration in the sorbent phase on the adsorption of microquantities of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu nitrates from HNO3 solutions by CIOP modified with TODGA was considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanides(III) adsorption from moderate-concentration HNO3 solutions increases with increasing atomic number of the element. The process of lanthanides(III) adsorption is exothermic, spontaneous and followed a pseudo-second-order kinetic model.

Hydrodynamics and oscillation of temperature in single crystal growth from high-temperature solutions with use of ACRT

Abstract The work presents the results of investigation of liquid phase hydrodynamics and temperature oscillations in a flux at accelerated rotation of a cylindrical crucible with a feeder. The dependences of shape and value of temperature oscillations in flux on the parameters of crucible rotation and temperature gradient were studied. The empirical dependence of temperature oscillation amplitude in a flux of the PbO-CaO/Bi 2 O 3 -Fe 2 O 3 /V 2 O 5 system at the bottom of a crucible on the rotation parameters were obtained as well as the values of maximal temperature differential in the melt height.

Study of the K2Ni(SO4)2 ∙ 6H2O–K2Co(SO4)2 ∙ 6H2O–H2O diagram and determination of the conditions for growing K2(Ni,Co)(SO4)2 ∙ 6H2O mixed crystals

The phase diagram of the K2Ni(SO4)2 · 6H2O–K2Co(SO4)2 · 6H2O–H2O ternary system is investigated in the temperature range of 30–70°С, and a relationship between the compositions of the equilibrium phases of the K2CoxNi(1–x)(SO4)2 · 6H2O (KCNSH) solid solution and the growth solution is established. It is shown how the salt compositions of the liquid and solid phases change during crystal growth upon slow cooling of solution. A dependence of the lattice parameters of the KCNSH solid solution on the concentration of isomorphic components is experimentally found.