Growth and optical characterizations of (Ba0.32Sr0.68)5Nb4O15 crystal

(Ba_0.32Sr_0.68)₅Nb₄O₁₅ crystal with sizes of Ø 17 × 35 mm was grown successfully by Czochralski technique method. The thermal anisotropy was discussed. The principal coefficients of thermal expansion along (100), (010), (001) directions were precisely measured to be 1.308 × 10^− 5, 1.288 × 10^− 5, 1.478 × 10^− 5 K^− 1, respectively. Its optical transparency range has been measured and found to span from 323 to 5500 nm. The bands present in the IR spectra were identified and assigned to the corresponding vibration modes of NbO₆ anions.     

Surface and grain-boundary energies as well as surface mass transport in polycrystalline CeO2

The multiphase equilibration technique for the determination of the equilibrium angles that develop at the interphase boundaries of a solid–liquid–vapor system, has been used to calculate the surface and interfacial energies in polycrystalline CeO₂ and CeO₂/Cu system in argon atmosphere at the temperature range 1473–1773 K. Linear temperature functions were obtained by extrapolation, for the surface energy γ_sv (J/m²) = 2.465–0.563 × 10⁻³ T and the grain-boundary energy γ_ss (J/m²) = 1.687–0.391 × 10⁻³ T of the ceramic, as well as for the interfacial energy γ_sl (J/m²) = 2.623–1.389 × 10⁻³(T −1356 K) of the CeO₂/Cu system. Grain-boundary grooving studied on polished surfaces of CeO₂ annealed in argon atmosphere at the same temperature range has shown that surface diffusion was the dominant mechanism for the mass transport. The surface diffusion coefficient can be expressed according to the equation D_s (m²/s) = 3.82 × 10⁻⁴ exp(−308,250/RT).     

Thermal properties and infrared spectra analysis of monoclinic RbGd(WO4)2 single crystals

Monoclinic rubidium gadolinium bis(tungstate) single crystals, RbGd(WO₄)₂ (RGW), have been grown by the spontaneous nucleation from high-temperature solutions. The thermal properties were firstly studied by measuring DSC, TG and specific heat. The melting point was determined to be 1089 °C. The measured specific heat ranges from 0.141 J g^− 1 K^− 1 to 0.564 J g^− 1 K^− 1 in the temperature range from 60 °C to 700 °C, a value that is slightly smaller than that of KGd(WO₄)₂. An infrared spectrum of the crystal was recorded in the frequency range of 50 to 1000 cm^− 1 and all vibration frequency peaks were assigned.     

Preparation of double-doped BaCeO3 and its application in the synthesis of ammonia at atmospheric pressure

Perovskite-type oxides BaCe_0.90Sm_0.10O_3−δ (BCS) and BaCe_0.80Gd_0.10Sm_0.10O_3−δ (BCGS) were synthesized by the sol–gel method and characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Using the sintered samples as solid electrolytes and silver–palladium alloy as electrodes, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid-state proton-conducting cell reactor. The maximum rate of production of ammonia was 5.82×10⁻⁹ mol s⁻¹ cm⁻².     

Ca4REO(BO3)3 crystals for green and blue microchip laser generation: from crystal growth to laser and nonlinear optical properties

We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca₄REO(BO₃)₃ family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca₄Gd_1−xNd_xO(BO₃)₃) crystals. The process goes from Czochralski boule to 1 × 3 mm² chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca₄Gd_1−xY_xO(BO₃)₃ (Gd_1−xY_xCOB) (x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of ⁴F_3/2 → ⁴I_9/2 Nd³⁺ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO₃) at 930 nm, Nd:YAG (Y₃Al₅O₁₂) at 946 nm, and Nd:ASL (Nd_ySr_1−x La_x−yMg_x Al_12−xO₁₉) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations.     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.     

Growth and spectral properties of Er:NaGd(WO4)2 crystal

A high optical quality Er³⁺-doped NaGd(WO₄)₂ single crystal with dimensions of ∅18 × 50 mm³ has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er³⁺ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm.     

Rib waveguides based on Zn-substituted LiNbO3 films grown by liquid phase epitaxy

The fabrication of epitaxially grown Zn-substituted LiNbO₃ (Zn:LiNbO₃) waveguide films and rib waveguides is reported and detailed investigations about microstructure, morphology and optical waveguide properties are provided. Zn:LiNbO₃ films were grown on congruent X-cut LiNbO₃ substrates by a modified liquid phase epitaxy in solid–liquid coexisting solutions. The homogeneously Zn-substituted films exhibit high crystalline perfection and extremely flat surfaces with averaged surface roughness of rms = 0.2–0.3 nm. At the film/substrate interface a Zn-containing transient layer has been observed, which allows the growth of elastically strained Zn:LiNbO₃ film lattices. X-ray diffraction reciprocal-space measurements prove the pseudomorphic film growth. The refractive index difference between substrate and film depends on the zinc substitution content, which increase with rising growth temperatures. For films with 5.3 mol% Zn (Δn_o ≈ +5 × 10⁻³) only ordinary ray propagation was observed, while for films with 7.5 mol% Zn (Δn_o ≈ +8 × 10⁻³, Δn_e ≈ +5 × 10⁻³) both modes, TM and TE propagate. Stress-induced refractive index changes are in the order of Δn ≈ 10⁻⁴. In rib waveguide microstructures singlemode propagation with nearly symmetrical field distribution has been observed. To demonstrate the potential of the proton exchange-assisted dry-etching technique interferometer microstructures were fabricated.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.     

Meteorological variations of PM2.5/PM10 concentrations and particle-associated polycyclic aromatic hydrocarbons in the atmospheric environment of Zonguldak, Turkey

Airborne particulate matter (PM_2.5 and PM₁₀) concentrations were measured in Zonguldak, Turkey from January to December 2007, using dichotomous Partisol 2025 sampler. Collected particulate matter was analyzed for 14 selected polycyclic aromatic hydrocarbons (PAHs) by high-performance liquid chromatography with fluorescence detection (HPLC-FL). The seasonal variations of PM_2.5 and PM₁₀ concentrations were investigated together with their relationships with meteorological parameters. The maximum daily concentrations of PM_2.5 and PM₁₀ reached 83.3 μg m⁻³ and 116.7 μg m⁻³ in winter, whereas in summer, they reached 32.4 μg m⁻³ and 66.7 μg m⁻³, respectively. Total concentration of PM₁₀-associated PAHs reached 492.4 ng m⁻³ in winter and 26.0 ng m⁻³ in summer times. The multiple regression analysis was performed to predict total PM_2.5- and PM₁₀-associated PAHs and benzo(a)pyrene-equivalent (BaPE) concentrations with respect to meteorological parameters and particulate mass concentrations with the determination coefficients (R²) of 0.811, 0.805 and 0.778, respectively. The measured mean values of concentrations of total PM_2.5- and PM₁₀-associated PAHs were found to be 88.4 ng m⁻³ and 93.7 ng m⁻³ while their predicted mean values were found to be 92.5 ng m⁻³ and 98.2 ng m⁻³, respectively. In addition, observed and predicted mean concentration values of PM_2.5-BaPE were found to be 14.1 ng m⁻³ and 14.6 ng m⁻³. The close annual mean concentrations of measured and predicted total particulate related PAHs imply that the models can be reliably used for future predictions of particulate related PAHs in urban atmospheres especially where fossil fuels are mainly used for heating.     

Thermal and mechanical properties of novel substrate crystal Mg0.4Al2.4O4

Mg_0.4Al_2.4O₄ single crystal was grown by the Czochralski method. The measured specific heat values are 0.804-1.06 J g^− 1 K^− 1 in the temperature range from 298.15 to 573.15 K. The calculated thermal conductivity components are 11.37, 11.47 and 10.77 W m^− 1 K^− 1 along the [111], [004] and [22?0] direction at 298.15 K. The Vickers microhardness values are 1328-1414 kg mm^− 2. These experimental results show that Mg_0.4Al_2.4O₄ crystal is a promising substrate for GaN-based LEDs.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Large-scale hydrothermal synthesis of WO3 nanowires in the presence of K2SO4

WO₃ nanowires were fabricated by a hydrothermal method in the presence of K₂SO₄. The nanowires exhibit a well crystallized one-dimensional structure with 10 nm in diameter and several microns in length. Effects of other alkali salts (KNO₃, NaNO₃ and Na₂SO₄) on the morphologies of WO₃ nanocrystals were also investigated. The important role of K₂SO₄ salt in the WO₃ nanowires synthesis has been demonstrated.     

CdWO4 bolometers for double beta decay search

In the field of Double Beta Decay (DBD) searches, the possibility to have high resolution detectors in which background can be discriminated is very appealing. This very interesting possibility can be largely fulfilled in the case of a scintillating bolometer containing a Double Beta Decay emitter whose transition energy exceeds the one of the natural gamma line of ²⁰⁸Tl.We present the latest results obtained in the development of such a scintillating bolometer. For the first time, an array of five CdWO₄ (¹¹⁶Cd has a Double Beta Decay transition energy of 2805 keV) crystals is tested. The array consists of a plane of four 3 × 3 × 3 cm³ crystals and a second plane consisting of a single 3 × 3 × 6 cm³ crystal. This setup is mounted in hall C of the National Laboratory of Gran Sasso inside a lead shielding in order to reduce as far as possible the environmental background. The aim of this test is to demonstrate the technical feasibility of this technique through an array of detectors, and perform a long background measurement in the best conditions in order to prove the achievable background in the 0νDBD region.     

Mechanical and dielectric properties of porous Si3N4–SiO2 composite ceramics

In order to prepare a structural/functional material with not only higher mechanical properties but also lower dielectric constant and dielectric loss, a novel process combining oxidation-bonding with sol–gel infiltration-sintering was developed to fabricate a porous Si₃N₄–SiO₂ composite ceramic. By choosing 1250 °C as the oxidation-bonding temperature, the crystallization of oxidation-derived silica was prevented. Sol–gel infiltration and sintering process resulted in an increase of density and the formation of well-distributed micro-pores with both uniform pore size and smooth pore wall, which made the porous Si₃N₄–SiO₂ composite ceramic show both good mechanical and dielectric properties. The ceramic with a porosity of 23.9% attained a flexural strength of 120 MPa, a Vickers hardness of 4.1 GPa, a fracture toughness of 1.4 MPa m^1/2, and a dielectric constant of 3.80 with a dielectric loss of 3.11 × 10⁻³ at a resonant frequency of 14 GHz.     

Effect of oxygen pressure of SiOx buffer layer on the electrical properties of GZO film deposited on PET substrate

The present work was made to investigate the effect of oxygen pressure of SiO_x layer on the electrical properties of Ga-doped ZnO (GZO) films deposited on poly-ethylene telephthalate (PET) substrate by utilizing the pulsed-laser deposition at ambient temperature. For this purpose, the SiO_x buffer layers were deposited at various oxygen pressures ranging from 13.3 to 46.7 Pa. With increasing oxygen pressure during the deposition of SiO_x layer as a buffer, the electrical resistivity of GZO/SiO_x/PET films gradually decreased from 7.6 × 10^− 3 to 6.8 × 10^− 4 Ω·cm, due to the enhanced mobility of GZO films. It was mainly due to the grain size of GZO films related to the roughened surface of the SiO_x buffer layers. In addition, the average optical transmittance of GZO/SiO_x/PET films in a visible regime was estimated to be ~ 90% comparable to that of GZO deposited onto a glass substrate.     

Up-conversion emission in KGd(WO4)2 single crystals triply-doped with Er/Yb/Tm, Tb/Yb/Tm and Pr/Yb/Tm ions

Triply-doped single crystals KGd(WO₄)₂:Er³⁺/Yb³⁺/Tm³⁺, KGd(WO₄)₂:Tb³⁺/Yb³⁺/Tm³⁺ and KGd(WO₄)₂:Pr³⁺/Yb³⁺/Tm³⁺ were grown by the Top Seeded Solution Growth (TSSG) method, with an aim of getting efficient up-converted multicolored luminescence, which subsequently can be used for generation of white light. Such an aim determined the choice of the triply doped compounds: excitation of the Yb³⁺ ions in the infrared spectral region is followed by red, green and blue emission from other dopants. It was shown that all these systems exhibit multicolor up-conversion fluorescence under 980 nm laser irradiation. Detailed spectroscopic studies of their absorption and luminescence spectra were performed. From the analysis of the dependence of the intensity of fluorescence on the excitation power the conclusion was made about significant role played by the host’s conduction band and other possible defects of the KGd(WO₄)₂ crystal lattice in the up-conversion processes.     

Visible quantum cutting via downconversion in a novel green-emitting K2Gd(WO4)(PO4):Tb phosphor

A novel phosphor K₂Gd(WO₄)(PO₄):Tb was prepared via a solid-state reaction. The crystal structure of K₂Gd(WO₄)(PO₄) as a new host matrix for luminescence was defined to be the orthorhombic system with space group Ibca (73). Visible quantum cutting under Tb³⁺ 4f⁸–4f⁷5d¹ excitation and host excitation in K₂Gd(WO₄)(PO₄):Tb³⁺ via a downconversion was identified. In order to rationalize the quantum cutting effect, the proper mechanism was proposed. According to calculations, the quantum efficiency was up to 183.2% and 176.4% under excitation at 235 nm and 150 nm, respectively. When compared with Zn₂SiO₄:Mn²⁺ (P1-G1S), KGWP:0.5Tb³⁺ is slightly less bright over 450–650 nm but has a shorter decay time.     

Polarized spectral properties of Tm:K5Bi(MoO4)4 crystal

Trivalent thulium-doped K₅Bi(MoO₄)₄ single crystals were grown by the Czochralski method. Its polarized absorption and fluorescence spectra and fluorescence decay curves were recorded at room temperature. On the basis of the Judd-Ofelt theory, the spectral parameters of the Tm³⁺:K₅Bi(MoO₄)₄ crystal were calculated. The cross relaxations between Tm³⁺ ions were analyzed. The emission cross sections of the ³F₄ → ³H₆ transition were obtained by the Fuchtbauer-Ladenburg formula and then the gain cross sections around 1.9 μm were calculated. The peak emission cross section and width of emission band around 1.9 μm are comparable to those for Tm³⁺:YAG and the tunable range is about 280 nm for the potential ∼1.9 μm laser operation via the ³F₄ → ³H₆ transition.     

Analyses of nano-crystalline LiCoVO4 prepared by solvothermal reaction

LiOH·H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ were used to prepare nano-crystalline LiCoVO₄ by 150 °C solvothermal reaction in isopropanol for 10–360 h and subsequent calcination at 300–500 °C for 6 h. XRD, TEM and selected area electron diffraction (SAED) revealed the presence of nano-crystalline LiCoVO₄ with inverse spinel structure. The V–O stretching vibration modes of VO₄ tetrahedrons were detected by FTIR over the range 617–835 cm^− 1 and by Raman spectrometer at 805.7 and 783.1 cm^− 1. Co, V and O were detected by EDX. TGA of solvothermal products shows weight loss due to the evaporation and decomposition processes at 40–648 °C.