Physical properties of whitlockite-type Ca3 (VO 4 ) 2 orthovanadate can be modified by incorporation of isovalent or aliovalent cation substituents. In this paper, the features of the crystal structure of Ca9La(VO4)7 and Ca10Li(VO4)7 whitlockite-type crystals grown by the Czochralski method with substitution by aliovalent La or Li ions are studied. Refinement of the structure using the Rietveld approach allowed us to determine the unit cell parameters and site occupancy. According to the data of polarization-optical studies, the formation of a strip-like ferroelectric domain structure with spontaneous polarization parallel to the third-order axis was established in the Ca9La(VO4)7 single crystal. It has been established that Ca10Li(VO4)7 is an antiferroelectric at room temperature. The correlations between Vickers hardness and fracture toughness values and the degree of crystal perfection are discussed.

In this article we report on a detailed study of the internal radioactive and chemical contamination of the Li6Eu(BO3)(3) scintillating crystal operated as a cryogenic scintillating bolometer over 359 h. The excellent discrimination power of the detector allows to distinguish effectively beta/gamma events from alpha events. Whilst a weak activity of daughter nuclides from U/Th chains at the level few mBq/kg was observed, this crystal was found to be significantly contaminated by Sm-147, an alpha-active nuclide, at the level of about 0.5 Bq/kg. The light yield for beta/gamma events was determined to be 7.4(6) keV/MeV. The light yield and quenching factor for alpha particles vary in the range of (0.5-1.2) keV/MeV and (0.07-0.17), respectively, due to energy dependence of the emitted scintillating light in the energy interval (2.0-7.0) MeV. The integral luminescence intensity of the Li6Eu(BO3)(3) crystal increases by more than four times only at low temperatures, below 80 K. Therefore, the Li6Eu(BO3)(3)-based cryogenic scintillating bolometers can be attractive detectors for direct neutron flux monitoring, to search for rare alpha decays or solar axions.

In this work, the temperature and high-pressure behaviors of Mn3+-doped garnet-type Ca3Ga2Ge3O12 single crystals have been investigated by means of photoluminescence and Raman spectroscopy, respect...

A PbMoO4 single crystal as a perspective detector for neutrinoless double beta decay experiment was grown by the Czochralski technique from high purity raw materials including archaeological lead. Charge trapping and energy transfer phenomena in this crystal have been studied by electron paramagnetic resonance (EPR) and wavelength-resolved thermally stimulated luminescence (TSL). EPR revealed several impurities, which however do not participate in the charge trapping processes: Gd3+, Cr3+, Mn2+. Self-trapped electron and (MoO4)3--VPb centers creation under laser light was confirmed. At least six glow peaks related to the thermal release of the charge carriers were observed having maxima at 41 K, 53 K, 83 K, 90 K, 105 K and 118 K. The peak at 41 K was ascribed to the de-trapping of self-trapped electrons. The 53 K one, in particular, is created by re-trapping processes. Partial cleaning procedure followed by the initial rise method allow to determine the trap depths and frequency factors for the 90 K and 105 K glow peaks. They have been referred to the (MoO4)3--VPb decay. A three-component analysis of the spectra could explain the observed 100 nm red shift of the thermo-luminescence emission maximum.

We study the nature of the intensity parameter Ω2 and the associated line strength S of the 4I9/2 → 4G5/2 hypersensitive transition in the series of Nd3+ doped Ca9Ln(VO4)7 and Ca10A(VO4)7 double calcium orthovanadate crystals. It has been shown that the covalence of neodymium – ligand bonds has a weak effect on Ω2 and S. They are mainly determined by the symmetry of the local environment of the neodymium ions, which lowers from yttrium ion to lanthanum ion for Ca9Y/La/Nd(VO4)7 crystals and from potassium ion to lithium ion in a series of Ca10K/Li(VO4)7 crystals.

YCOB:Er (2 at.%), Yb (20 at.%) single crystal with a diameter of 15 mm and a length of 55 mm was grown by the Czochralski method. The crystal structure of the obtained sample was specified by the method of powder diffractometry. Type I and type II micro-hardness anisotropy was studied by the Vickers method for the faces (010) and (111). Inhomogeneity of the mechanical properties of YCOB crystal was shown to be defined by the orientation of the boron-oxygen bonds in the crystal lattice.

The search for new crystalline host materials for the usage in lasers emitting in the eye-safe spectral range of 1.5–1.6 µm is an important task. The aim of this work was to study the growth technique, spectroscopic properties and laser characteristics of new active media – crystals Er3+,Yb3+:Ca2RE2(BO3)4 (RE=Y, Gd).Calcium-yttrium Er3+,Yb3+:Ca3Y2 (BO3)4 (CYB) and calcium-gadolinium Er3+,Yb3+: Ca2 Gd 2(BO3)4 (CGB) oxoborate crystals co-doped with erbium and ytterbium ions were investigated. Polarized absorption and emission cross-section spectra were determined. The lifetimes of 4I11/2 and 4I13/2 energy levels of Er3+ ions were measured and ytterbium-erbium energy transfer efficiencies were estimated. The calculation of the gain cross-section spectra was performed. By using of Er3+,Yb3+: Ca2 RE 2(BO3)4 (RE=Y, Gd) crystals the laser performance was realized, for the first time to the best of our knowledge. The laser characteristics were studied in a quasi-CW (QCW) laser operation.The wide band with a peak at the wavelength of 976 nm is observed in the absorption spectra of both crystals. This peak coincides with the emission wavelength of the pump laser diodes for Yb-doped active media. The maximum value of absorption cross-section was 1.7 × 10–20 cm2 for polarization E // b for both crystals. The lifetimes of the upper laser level 4I13/2 of Er3+ ions were 580 ± 30 μs and 550 ± 30 μs for Er,Yb:CYB and Er,Yb:CGB crystals, respectively. The energy transfer efficiencies from ytterbium to erbium ions for an Er,Yb:CYB and Er,Yb:CGB crystals were 94 % and 96 %, respectively. According to gain spectrum of the Er,Yb:CYB crystal the gain band peak is centered at the wavelength of 1530 nm. The maximum QCW output power was 0.5 W with slope efficiency of 13 % regarding to absorbed pump power for an Er,Yb: CYB crystal. The laser beam parameter M2 did not exceed < 1.5.Based on the obtained results, it can be concluded that these crystals are promising active media for lasers emitting in the spectral range of 1.5–1.6 μm for the usage in laser rangefinder and laser-induced breakdown spectroscopy systems, and LIDARs.

Crystal structure, thermal, ionic conductivity of large cations (Ca and Pb), dielectric and non-linear optical properties were investigated for Ca10.5−xPbx(VO4)7single crystals (x= 1.9, 3.5, 4.9).

Calcium-yttrium oxyborate single crystals YCa 4 O(BO 3 ) 3 co-doped erbium and ytterbium ions (Er,Yb:YCOB) (1,5 aT.% Er 3+ , 30 aT.% Yb 3+ and 2 aT.% Er 3+ , 20 aT.% Yb 3+ ) were grown by Czochralski method. Absorption and photoluminescence properties of the Er, Yb: YCOB crystals were studied. The emergence of intensive luminescence near 1,5 μm indicates the effective energy transfer from the multiplets 2 F 5/2 of the Y b3+ ions to the 4 I11/2 states of Er 3 + ions when pumping in the absorption band of ytterbium (940 nm). For the first time in the crystalline material Er, Yb: YCOB, a single pulse lasing in a Q-switch mode with the use of passive modulators based on Co: MALO was obtained.

Thermal conductivities of M WO 4 ( M = Ca, Cd, or Ba), NaGd(WO 4 ) 2 :1 at % Er, NaGd(WO 4 )2:2 at % Yb, and NaLa 0.5 Gd 0.5 (WO 4 ) 2 :2 at % Nd single crystals have been experimentally investigated in the temperature range of 50–300 K.

Abstract Single crystals of Ca9Y(VO4)7 (1), Ca9Y(VO4)7:Li+ (2) and Ca9Y(VO4)7:Mg2+ (3) were grown by the Czochralski method. Their chemical composition was analyzed by ICP spectroscopy and their crystal structure was examined by single crystal X-ray analysis. The crystals are characterized by trigonal symmetry, space group R3c. Hexagonal unit-cell parameters are as follows: a=10.8552(1) Å, c=38.0373(2) Å, V=3881.65(1) Å3 for 1; a=10.8570(1) Å, c=38.0161(3) Å, V=3880.77(4) Å3 for 2; a=10.8465(1) Å, c=38.0366(2) Å, V=3875.36(3) Å3 for 3. All crystals are characterized by β-Ca3(PO4)2-type structure with statistical distribution of Ca2+ and Y3+ over M1, M2 and M5 sites in different ratios and with completely empty M4-cationsite. The impurity of Mg2+cations in structure 2 has been detected in octahedral M5 site. Ferroelectric phase transitions are evidenced by DSC and SHG. At about 1220 and 1300 K, they demonstrate phase transitions. Upon heating the symmetry of the crystal structure changes according to the scheme R3c→R3̅c→R3̅m and is restored during consequent cooling. The first of them is of ferroelectric and the second of non-ferroelectric nature. Even a small amount of impurities in Ca9Y(VO4)7 structure is accompanied by a noticeable decrease in the temperature of the ferroelectric-paraelectric phase transition.

Crystal growth and thermal properties of binary borates, Ca3RE2(BO3)4 (RE = Y, Gd, Nd), are considered promising crystals for laser applications. These single crystals were grown by the Czochralski method. The crystal and defect structure were characterized. Volumetric chemical methods without prior separation of the components were developed and applied for the determination of the dependence of chemical compositions of the crystals on the growth conditions. The thermal conductivity was investigated in the 50–300 K range. The character of the temperature dependence of thermal conductivity was found to be similar to that of glass. The possible reasons of the observed features of the thermal conductivity were analyzed.

The Ca9RE(VO4)(7) (RE = La, Nd, Gd) and Ca10M(VO4)(7) (M = Li, Na, K) single crystals have been grown by the Czochralski method. The binary vanadates are isostructural to "whitlockite" mineral (rhombohedral symmetry, R3c space group). Their thermal conductivity has been investigated in the range 50K-300K parallel to the c axis. For Ca9Gd(VO4)(7) crystals, the thermal conductivity has been investigated in the range 300K-550K also. Additionally, for the Ca10M(VO4)(7) (M = Li, Na, K) crystals the heat capacity has been studied in the temperature range 80K-300K. The character of the temperature dependence of thermal conductivity is close to that of glasses. The possible reasons of the observed features of the thermal conductivity have been analyzed. Raman spectra of Ca10M(VO4)(7) (M = Li, Na, K) crystals have been measured and discussed. The spectral lines were broad and similar to polycrystalline or amorphous solids. These crystals are expected to be suitable for application as efficient nonlinear optic and laser materials.

The SrWO4 and CaMoO4 crystals grown under different conditions by the Czochralski method were studied by means for Raman spectroscopy. Raman spectra of the crystals were measured and peaks were identified. For SrWO4 crystals 2nd and 3rd Stokes were observed for the first time.

The \(\hbox {Ca}_{9}\hbox {RE}(\hbox {VO}_{4})_{7}\) (RE \(=\) La, Nd, Gd) and \(\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}\) (M \(=\) Li, Na, K) single crystals have been grown by the Czochralski method. The binary vanadates are isostructural to “whitlockite” mineral (rhombohedral symmetry, R3c space group). Their thermal conductivity has been investigated in the range 50 K–300 K parallel to the c axis. For \(\hbox {Ca}_{9}\hbox {Gd}(\hbox {VO}_{4})_{7}\) crystals, the thermal conductivity has been investigated in the range 300 K–550 K also. Additionally, for the \(\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}\) (M \(=\) Li, Na, K) crystals the heat capacity has been studied in the temperature range 80 K–300 K. The character of the temperature dependence of thermal conductivity is close to that of glasses. The possible reasons of the observed features of the thermal conductivity have been analyzed. Raman spectra of \(\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}\) (M \(=\) Li, Na, K) crystals have been measured and discussed. The spectral lines were broad and similar to polycrystalline or amorphous solids. These crystals are expected to be suitable for application as efficient nonlinear optic and laser materials.

The Ca9Y(VO4)(7-x)(PO4)(x) (x = 0, 1, 3, 4) solid solution whitlockite-like single crystals have been grown by the Czochralski method from mixtures of single phase Ca9Y(VO4)(7) and Ca9Y(PO4)(7) starting materials produced by solid-state synthesis. Real compositions of solid solution crystals has been determined and analyzed. It is found that crystals with x = 0, 1, 4 exist with polar structure at room temperature, space group R3c. At least one of them, Ca9Y(VO4)(7), demonstrates ferroelectric behaviour with phase transition at 942 degrees C. Unlike the others, Ca9Y(VO4)(3)(PO4)(4) crystallizes in centrosymmetric whitlockite-like structure with space group R3c confirmed by single-crystal X-ray structure analysis. Similar to other whitlockite-family phosphates and vanadates, its crystal structure is described as a disordered structural version of usual whitlockites, corresponding to their high-temperature paraelectric phases. The transmission and luminescence spectra of solid solution crystals are reported, the hardness H-v and fracture toughness K-1c of solid solution single crystals are also determined. (C) 2017 Elsevier B.V. All rights reserved.

Whitlockite is a phosphate mineral of Ca9(MgFe)(PO4)6PO3OH formula, known for its presence in granitic pegmatites and phosphate rock deposits, and in living organisms. Recently, various anhydrous synthetic phosphates and vanadates crystallizing in structures related to that of whitlockite have been studied as materials possibly applicable as phosphors in light-emitting diodes and having a potential in laser engineering as a promising host for active laser media, and nonlinear optics. One of studies compound families is described by the formula Ca9(Nd)(VO4)7. The studied sample of Ca9(Nd)(VO4)7 was a transparent, violet monocrystal grown by the Czochralski method in inert argon atmosphere. Recently done Raman and XRD studies revealled compositional differences that separate this specific type of whitlockite from others in its family. This brittle (Mohs 5), piezoelectric and pyroelectric material has trigonal crystallographic structure and ditrigonal pyramidal crystal class – it belongs to noncentrosymmetric R3c space group. These crystals are also characterized by polymorphic transition from the noncentrosymmetric to the centrosymmetric phase which occurs roughly between 800-1100oC at ambient pressure however no signs of pressure-induced phase transition were detected in this study. High pressure luminescence spectra excited by 532 nm radiation show typical lines of Nd associated with transitions from F3/2 to I9/2, I11/2, I13/ levels in this material [1-4], which exhibit pressure coefficients in the range of 4 – 7 cm/Gpa. High-pressure micro-Raman spectra of Ca9Nd(VO4)7 single crystal were examined in this work at room temperature on Monovista CRS+ S&I spectrometer with use of diamond-anvil cell (Diacell CryoDAC-LT) and argon as a pressure transmitting medium. The applied pressure reached 15 GPa. The excitation was provided by green (532 nm) and red (785 nm) lasers. At pressure between between 50 and 60 kbar, additional lines appear in the spectra. Signals emerging at 425 and 665 cm could be also strictly related to the high-pressure activation of neodymium ions. Origin of these lines is discussed in this work.