V. A. Krut’ko

Synthesis and luminescence of ultrafine Er3+- and Yb3+-doped Gd11SiP3O26 and Gd14B6Ge2O34 particles for cancer diagnostics

In search of new contrast materials for NMR and fluorescence diagnostics and neutron capture therapy of cancer, we have synthesized ultrafine Er3+- and Yb3+-doped Gd11SiP3O26 and Gd14B6Ge2O34 particles and studied their luminescence properties. We measured the Er3+ upconversion luminescence spectra of the gadolinium erbium ytterbium phosphosilicates and borate germanates in the visible range and evaluated the absolute quantum yield of their luminescence. The quantum yield of luminescence in the gadolinium phosphosilicate Gd11SiP3O26 doped with 5.0 at % Yb and 2.5 at % Er is comparable to that in known Yb3+/Er3+ codoped fluorides. The nonradiative Yb3+ → Er3+ energy transfer efficiency is evaluated.

Phase Relations in the Solidus Region of the SrO-Bi2O3-B2O3 System

Phase equilibria in the SrO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction analysis and DTA. Ternary compounds SrBiBO4 and Sr7Bi8B18O46 congruently melting at 820 ± 5°C and 760 ± 5°C have been found. Quasi-binary sections are determined and the isothermal section of the system in the region Bi2O3-Sr2Bi2O6-Sr3B2O6-B2O3 at 600°C has been constructed.

Structure effect on the absorption and circular dichroism spectra of Sm14B6Ge2O34 crystals

The spectroscopic and chiroptical properties of rare-earth-rich borate germanate crystals of composition Sm14B6Ge2O34 have been studied for the first time. The absorption and circular dichroism spectra of the crystals have been measured. For some of the f-f transitions involved, we have calculated the dipole strength and optical rotatory power.

Nanostructuring in the Process of the Formation of Mixed-Anion Compounds: Rare-Earth Borogermanates, Germanophosphates, and Borotungstates

Specific features of the textures (the preferred orientation of the nanometer building blocks) in the structures of mixed-anion compounds—rare-earth borogermanates, germanophosphates, and borotungstates that arise from the acid-base interaction in the Ln2O3-B2O3-GeO2, Ln2O3-GeO2-P2O5, and Ln2O3-B2O3-WO3 systems (Ln = La-Gd)—have been studied. Based on characteristic texture traits, the mixed-anion compounds of early rare-earth elements can be divided into three groups: (i) Ln2O3: ExOy > 1, (ii) Ln2O3: ExOy = 1, and (iii) Ln2O3: ExOy < 1. Because of the dominant structural effect of the basic oxide Ln2O3 in the compounds of the first group, the structures of Nd14O8(BO3)6(GeO4)2 and Pr11O10(GeO4)(PO4)3 are composed of infinite [LnOn] bands and layers and discrete groups [EOm] located in the interband and interlayer spaces. The dominant structural effect of the acid oxides [ExOy] in the compounds of the third group leads to the appearance of ring textures composed of [LnOn], as well as to the appearance of chains and networks composed of [EOm], in the structures of Ln(BGeO5) and Ln(BO2)(WO4).

Structures of nonlinear hexagonal boratotungstates Ln3BWO9 (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy)

Polycrystalline boratotungstates of composition Ln3BWO9 (Ln = Pr, Nd, Sm, Gd, Tb, Dy) are prepared by solid-phase synthesis and structurally studied. The structures are refined using the Rietveld method for hexagonal space group P63 (Z = 2). The boratotungstate structures are frameworks. The rare-earth cations in the structure are coordinated by an array of nine oxygen atoms (three oxygen atoms from borato groups BO3 and six from WO6 polyhedra). The nature of the optical nonlinearity in the hexagonal boratotungstates Ln3BWO9 is a direct consequence of the acentricity of both the tungstate and the rare-earth polyhedra in the structure. Dimorphism is discovered in polycrystalline La3BWO9.

Gel combustion synthesis of LaxGd14–xB6Ge2O34 (x = 3 and 4) codoped with Yb3+–Er3+ and Yb3+–Tm3+ active ions

This paper reports the gel combustion synthesis of LaxGd14–xGe2B6O34 (x = 3 and 4) germanate borates codoped with Yb3+–Er3+ and Yb3+–Tm3+ active ions. The synthesized compounds are isostructural with Gd14Ge2B6O34 and crystallize in trigonal symmetry (sp. gr. P31). We have determined the unit-cell parameters of the synthesized mixed-cation germanate borates La3Gd9.74Yb0.84Tm0.42Ge2B6O34 (a = b = 9.794 Å, c = 25.7913 Å, V = 2143 Å3) and La3.16Gd10Yb0.7Er0.14Ge2B6O34 (a = b = 9.746 Å, c = 25.7450 Å, V = 2118 Å3) and assessed their thermal stability. The results demonstrate that the LaxGd14–xGe2B6O34 (x = 3 and 4) germanate borates codoped with Yb3+–Tm3+ and Yb3+–Er3+ active ions melt congruently at T = 1660 and 1700 K and crystallize with undercooling at T = 1620 and 1660 K, respectively. We have obtained an upconversion luminescence spectrum of the La3.16Gd10Yb0.7Er0.14Ge2B6O34 germanate borate. The spectrum shows two bands. The stronger band (in the green region) corresponds to two transitions: 2H11/2 → 4I15/2 (λ = 525 nm) and 4S3/2→ 4I15/2 (λ = 550 nm). The weaker band (in the red region) corresponds to the Er3+ 4F9/2→ 4I15/2 transition.

Structure of the La12GdEuB6Ge2O34 borogermanate as probed by NMR and IR spectroscopy

The structure of fine crystalline borogermanate La12GdEuB6Ge2O34 has been studied by NMR and IR spectroscopy. It has been demonstrated that this compound is isostructural to the homonuclear Ln14B6Ge2O34 compounds (Ln = Pr-Gd) and crystallizes in space group P31. The rare-earth elements have been distributed over the LnOn polyhedra in La12GdEuB6Ge2O34 by analogy with the known structures. Lanthanum can occupy positions with CN 7–10, and the symmetry of these LnOn coordination polyhedra is not higher than C2v. In the La12GdEuB6Ge2O34 structure, the LnOn coordination polyhedra are formed by oxygen atoms of oxo groups and anions, some of the oxygen atoms being shared by LnOn polyhedra. The BO3 and GeO4 groups in the structure are also bridging, i.e., are involved in bonding of LnOn polyhedra. One of the B-O bonds in La12EuGd(BO3)6(GeO4)2O8 is elongated as compared with the B-O bond lengths in homonuclear compounds Pr14(BO3)6(GeO4)2O8 and Nd14(BO3)6(GeO4)2O8. In the La12GdEuB6Ge2O34 structure, germanium is located in isolated GeO4 tetrahedra with distorted Td symmetry. The local symmetry of lanthanum in fine crystalline La12GdEuB6Ge2O34 have been assessed using 139La NMR (B0 = 7.04 T, room temperature). For comparison, binary lanthanum compounds with a simpler structure— LaBO3, La(BO2)3, and La2GeO5—have been used. The spectra of all compounds are rather broad (ν1/2 = 180–240 kHz). The 139La NMR spectra of the LaBO3, La(BO2)3, and La12GdEu(BO3)6(GeO4)2O8 borates show a signal at (1080 ± 40) ppm, which is absent in the spectrum of La2GeO5. The shape of the 139La NMR spectra of La12GdEu(BO3)6(GeO4)2O8 and LaBO3 is characterized by the second-order quadrupole splitting with a downfield shoulder. The similarity of these spectra points to close 139La NMR chemical shifts of La12GdEu(BO3)6(GeO4)2O8 and LaBO3. No quadrupole splitting was observed in the spectra of La(BO2)3 and La2GeO5.

Cationic networks in the structures of borates, tungstates, and borotungstates forming in the Ln2O3-B2O3-WO3 systems

The influence of the structures of binary compounds on the formation of ternary mixed-anion compounds—borotungstates—in ternary Ln2O3-B2O3-WO3 systems was studied. The structures of borotungstates either inherit the predominant type of cationic network from the structures of the binary compounds (anisotropic cationic networks in Ln (BO2)(WO4)) or represent a sum of equivalent anisotropic and isotropic cationic networks, forming combined cationic networks (in Ln3BWO9). In the lanthanide series, the ranges of existence of borotungstates coincide with the ranges of existence of the structure types most abundant in the binary compounds.

Phase relations in the CaO-Bi2O3-B2O3 system in the subsolidus region

Phase relations in the CaO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction and differential thermal analyses, and the isothermal section at 600°C has been constructed. The formation of ternary compounds at the component ratios 1CaO: 1Bi2O3: 1B2O3 (CaBi2B2O7) and 1CaO: 1Bi2O3: 2B2O3 (CaBi2B4O10) has been established X-ray diffraction characteristics of these phases are presented.

New, thermally stable Gd11(GeO4)(PO4)3O10-based upconversion phosphors

A series of Gd11–x–yYbxEryGeP3O26 germanate phosphates differing in the ratio of the Yb3+ and Er3+ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er3+2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (Ben) in Gd11–x–yYbxEryGeP3O26. The effects of the concentrations and ratio of the dopants in the Gd11(GeO4)(PO4)3O10 germanate phosphate host on Ben and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.