R. P. Ermakov

Coprecipitation from aqueous solutions to prepare binary fluorides

The synthesis of binary fluoride phases, specifically nanofluorides, by coprecipitation from aqueous solutions is considered in terms of phase equilibria. Phases have been precipitated in NaF-RF3 systems (where R stands for a rare-earth element), MF2-YF3 systems (where M = Ca, Sr, Ba), BaF2-ScF3, and CaF2-BaF2 systems. In the MF2-YF3 systems, unordered metastable congruently soluble phases are precipitated instead of ordered fluorite-like phases. In the BaF2-ScF3 system, the congruently soluble compound Ba3Sc2F12 is precipitated. In the NaF-RF3 systems, incongruently soluble metastable phases with a fluorite-like structure (for R = Er, Lu, Y) and the gagarinite structure (NaGdF4) are formed. In the CaF2-BaF2 system, intermediate phases have not been formed.

Synthesis of Ba4R3F17 (R stands for rare-earth elements) powders and transparent compacts on their base

Single-phase samples of Ba4R3F17 · nH2O (R = La, Ce, Pr, Nd, Eu, Gd, Y, Er, or Yb; n = 2.5−3.2) were prepared by coprecipitation from nitrate solutions using hydrofluoric acid. The phases crystallize in a fluorite-type face-centered cubic lattice. The dried precipitates are transparent. Scanning electron and atomic-force microscopy and X-ray diffraction line broadening show a hierarchic structure in the samples: primary nanoparticles join into agglomerates with characteristic sizes of about 150–200 nm, these agglomerates being self-packed into parallel layers with a thickness on the order of 500 nm.

Coprecipitation of barium-bismuth fluorides from aqueous solutions: Nanochemical effects

The BaF2-BiF3 system was studied by the method of coprecipitation from aqueous solutions. The region of precipitation of single-phase nonoxygen powders was revealed (the atomic fraction of Bi in the initial solution was 0.35–0.43). The composition of the cubic fluorite-type phase is BaBiF5 according to an energy-dispersive X-ray spectroscopy analysis. Samples prepared from solutions with high Bi concentrations contain oxygen. This indicates that the hydrolysis temperature of BiF3 decreases when compared with that of the bulk samples and that this process takes place at room temperature. The coherent intergrowth of nanoparticles with the formation of single crystals with nonfaceted complex forms was shown by scanning electron microscopy and transmission electron microscopy.

Synthesis and luminescent characteristics of submicron powders on the basis of sodium and yttrium fluorides doped with rare earth elements

Submicron powders of solid solutions on the basis of cubic and hexagonal phases existing in a NaF-YF3 system have been synthesized with the precipitation method from aqueous solutions at room temperature. The conditions for the preparation of single-phase samples have been determined. The upconversion luminescence spectra were investigated. The most promising composition is revealed (Na0.414Ca0.183Y0.215Yb0.094Er0.094F1.989), which demonstrates an upconversion luminescence quantum yield of 1.9% with a 3-W pump power at a 974-nm wavelength.

Synthesis and Characterization of Fluoride Xerogels

Using coprecipitation from aqueous solutions, we have synthesized transparent fluoride xerogels with both hexagonal (NdF3, PrF3, and CeF3; tysonite structure) and cubic (Sr0.6Y0.4F2.4, Ba4Y3F17:Bi, and Ba4Y3F17:Yb; fluorite structure) symmetries. As shown by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, the transparent xerogels have a hierarchical structural organization: primary nanoparticles 20–30 nm in size form agglomerates about 100 nm in size, which in turn form a “skeleton” with many voids and channels up to hundreds of nanometers in size.

Structure and phase composition of thin TiO2 films grown on the surface of metallized track-etched polyethylene terephthalate membranes by reactive magnetron sputtering

We have studied TiO2, Ag, Ag/TiO2, and Cu/TiO2 coatings grown on track-etched polyethylene terephthalate membranes. The metals and oxides were deposited by reactive vacuum sputtering using a planar magnetron. The microstructure of the samples were examined by scanning and transmission electron microscopy techniques. The elemental composition of the coatings were determined by energy dispersive X-ray microanalysis, and their phase composition was determined by X-ray diffraction at different temperatures and by transmission electron diffraction. Titanium dioxide can be present on the surface of track-etched membranes (TMs) in three forms: nanocrystals of tetragonal anatase with orthorhombic brookite and amorphous TiO2 impurities. The copper-metallized TM has been shown to contain cubic Cu2O. The optical properties of the composite membranes and films have been studied by absorption spectroscopy. The energies of direct and indirect allowed optical transitions have been evaluated from measured absorption spectra of the TiO2, Ag/TiO2, and Cu/TiO2 coatings.

Synthesis and Luminescence Characteristics of LaF 3 :Yb:Er Powders Produced by Coprecipitation from Aqueous Solutions

Hydrated lanthanum fluoride powders, both undoped, and doped with erbium and ytterbium fluorides (to a total content of 6–28 mol %), of the general formula RF3 · nH2O (n = 0.30 ± 0.01), crystallizing in the hexagonal system, were obtained by coprecipitation from aqueous solutions of the corresponding nitrates by the interaction with hydrofluoric acid. The dehydration is completed at 380°C. At 600°C, the concentrated solid solution decomposes to precipitate a phase with the structure of orthorhombic YF3. The efficiency of the upconversion luminescence of the powders, excited at a wavelength of 974 nm, is low.