Spectroscopic properties of red Bi4Ge3O12 by vertical Bridgman method

Red Bi₄Ge₃O₁₂ (BGO) single crystals had been grown by vertical Bridgman (VB) method. The structure of this crystal was determined by XRD. The absorption and emission spectra of the red BGO in visible and near infrared region (NIR) were measured at room temperature. The emission intensity of the red BGO is weaker than that of ordinary BGO at about 500 nm. Interestingly, the red BGO shows a significant emission band centered at about 1495 nm. The red BGO faded and its properties recovered after ultraviolet (UV) irradiation or annealing.     

Neutron diffraction investigation of Zr3Y4O12

Ordering of Zr₃Y₄O₁₂ has been investigated by x-ray and neutron diffraction techniques. Ordering is very sluggish as shown by the presence of both disordered cubic and ordered rhombohedral phases after annealing for three months at 1100°C. Refinement of neutron data for ordered Zr₃Y₄O₁₂ by the Rietveld profile technique confirms the structure reported by Scott.     

The perfection of bridgman-grown Bi4Ge3O12 crystals

Single crystals of Bi₄Ge₃O₁₂ were grown by the vertical Bridgman technique. As shown by X-ray diffraction line profiles these crystals exhibit a very high degree of perfection. Bi₄Ge₃O₁₂ is used as detector material for high energy radiation. Very perfect crystals are preferred because defects play a prominent role in radiation damage.     

Spectroscopic and laser properties of SrLaGa3O7:Pr crystals

The spectroscopic properties of trivalent praseodymium (Pr³⁺) doped SrLaGa₃O₇ (SLG) crystals have been investigated at various temperatures. Absorption, emission, excitation and lifetime measurements have been performed and discussed in the framework of the Judd-Ofelt approach. Stimulated emission cross sections for the strongest transitions of Pr³⁺ ion have been calculated. Stimulated emission has been observed for the first time in Pr³⁺ doped SLG crystal, we have obtained laser operation at 488 n, at cryogenic temperatures and at 645 nm at room temperature.     

Nd optical multisites in the Ca3(Nb,Ga)2Ga3O12 laser garnet crystal

Laser excited site-selective luminescence of Nd³⁺ ion in the Ca₃(Nb,Ga)₂Ga₃O₁₂ garnet crystal has been investigated for the and transitions. Six main non-equivalent crystal field sites were detected in the garnet. The crystal splitting scheme of the and manifolds was obtained for each Nd³⁺ site. Energy transfer between Nd³⁺ sites was observed by using time resolved spectroscopy.     

Growth of Ca3Fe2Ge3O12 and Ca3Fe(Al,Cr) Ge3O12 garnets in molten bismuth germanate glasses

Additions of Fe₂O₃ to CaO·Bi₂O₃·2 GeO₂ cause Ca₃Fe₂Ge₃O₁₂ garnets to precipitate from the resultant melt at 1250°C. Garnets with the composition Ca₃Fe(Al, Cr) Ge₃O₁₂ are also precipitated by adding either $\text{Al}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ or $\text{Cr}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ mixtures. The well-formed crystals range from several to 100 μm in size and are obtained in 50 to 70% yields at $\text{Fe}\text{Bi}\text{= 0.4}$. Additions of Fe₂O₃ (up to $\text{Fe}\text{Bi}\text{= 1.0}$) to compositions containing ZnO, CdO, SrO, and BaO yield only dark glasses. The physical properties of these glasses suggest that Fe(III), in contrast to AL(III) & Ga(III), prefers octahedral coordination.     

Thermal expansion studies of Gd2Mo3O12 and Gd2W3O12

Simultaneous thermogravimetric/differential thermal analysis of Gd₂Mo₃O₁₂ showed an irreversible phase transition at 1178 K where as Gd₂W₃O₁₂ showed reversible phase transition at 1433 K, which were confirmed by powder X-ray diffraction. The thermal expansion behavior of α-Gd₂Mo₃O₁₂ (room temperature phase), β-Gd₂Mo₃O₁₂ (phase obtained by heating Gd₂Mo₃O₁₂ at 1223 K) and Gd₂W₃O₁₂ have been investigated using high temperature X-ray diffractometer. The cell volume of α-Gd₂Mo₃O₁₂, β-Gd₂Mo₃O₁₂ and Gd₂W₃O₁₂, fit into polynomial expression with respect to temperature, showed positive thermal expansion up to 1073, 1173 and 1173 K, respectively. The average volume expansion coefficients for α-Gd₂Mo₃O₁₂, β-Gd₂Mo₃O₁₂ and Gd₂W₃O₁₂ are 39.52 × 10⁻⁶, 21.23 × 10⁻⁶ and 37.96 × 10⁻⁶ K⁻¹, respectively.     

Glass-recrystallization of ferroelectric Pb5Ge3O11

Thin plate-like crystals of ferroelectric Pb₅Ge_3?xSi_xO₁₁ (0 ≤ x ≤ 1.5) were prepared by a glass-recrystallization technique during which the glass was heat-treated at 600 to 720°C. The crystals show preferred orientation with the polar c-axis perpendicular to the sample surface, an ideal geometry for pyroelectric infrared detectors.     

Spectroscopic investigation of Nd ion in LiNbO3, MgO:LiNbO3 and LiTaO3 single crystals relevant for laser applications

The polarized absorption and luminescence properties of Nd³⁺ doped isostructural LiNbO₃, MgO:LiNbO₃ and LiTaO₃ nonlinear bulk single crystals are reported. Pump-probe experiments associated with the Judd-Ofelt approach are used to estimate two types of room temperature cross sections: polarized emission cross sections of the dominant ⁴F_3/2 → ⁴I_1//2 transition near 1085 and 1093 nm and polarized excited-state absorption cross sections in the same spectral domain and in the green spectral range corresponding to self frequency doubling. Self frequency-doubling results are also given in Nd:LiNbO₃ and Nd:MgO:LiNbO₃ versus sample temperature.     

Spectroscopic and glass transition investigations on Nd-doped NaF-Na2O-B2O3 glasses

New developments in photonic technology need new materials for various applications. In the present report, Nd³⁺-doped NaF-Na₂O-B₂O₃ glasses were prepared and the spectroscopic and glass transition properties were analysed. The Fourier transform infrared spectral studies reveal that the glass contains BO₃ and BO₄ units as the local structures and the Na⁺ ions as the network modifiers. The absorption studies were carried out by using Judd-Ofelt theory, the experimental and theoretical oscillator strengths were also calculated. The emission spectral study was done for the 1 mol% Nd-doped glass and the spontaneous emission probability and stimulated emission cross-sections for the , transitions were calculated using the J-O parameters.     

Effect of doping with Co2O3, TiO2, Fe2O3, and Mn2O3 on the properties of Ce0.8Gd0.2O2?δ

The effects of Co, Fe, Mn, and Ti oxide additions on the sinterability and crystal-chemical, thermal, and electrical properties of Ce_0.8Gd_0.2O_2−δ have been studied. The results indicate that these oxides enhance the sinterability of the mixed oxide, regardless of whether they were introduced before or after synthesis. The most effective sintering aid is Co₂O₃. The lattice parameters of Ce_0.8Gd_0.2O_2−δ samples containing different metal oxide additions (1 mol %) are refined in space group Fm3m. The temperature-dependent thermal expansion data are used to determine the linear thermal expansion coefficients of the samples. Manganese oxide additions reduce the electrical conductivity of Ce_0.8Gd_0.2O_2−δ, whereas the other dopants increase it in the order Ti < Fe < Co. The activation energy for conduction increases in the order Co < Ti < Fe < Mn. Original Russian Text ? E.Yu. Pikalova, A.N. Demina, A.K. Demin, A.A. Murashkina, V.E. Sopemikov, N.O. Esina, 2007, published in Neorganicheskie Material, 2007, Vol. 43, No. 7, pp. 830–837.     

Spectroscopic behavior of Nd in a new microcrystalline ZnY4W3O16 tungstate

In the framework of systematic investigations of the optical properties of a new tungstate ZnY₄W₃O₁₆ in which Y³⁺ cations allow for rare-earth ions doping, the compounds doped with neodymium Nd³⁺ ion were synthesized, analyzed and considered as a possible laser material. The crystalline stoichiometric sample of the chemical formula ZnNd₄W₃O₁₆ and their yttrium diluted analogues 0.5, 1, 5 and 10 mol% Nd³⁺-doped ZnY₄W₃O₁₆ were obtained by a solid-state reaction. X-ray powder diffraction analysis as well as the IR spectra were used to the structural characterization of the compounds. Electron microscopy has been used to analyze the grain size, the presence of aggregates, and the type of boundary between the microcrystals. In order to study spectroscopic properties, the high resolution absorption and emission spectra at room and low temperature were measured in visible and IR regions. The radiative transition probabilities in those tungstates were calculated and analyzed. Based on the 4 K absorption spectra in the range of ⁴I_9/2 → ²P_1/2 transition the number of metal sites occupied by the dopants was determined. The strong fluorescent emission involving the ⁴F_3/2 → ⁴I_9/2, ⁴I_11/2, ⁴I_13/2 transitions at 298 and 77 K were observed under pulsed laser and xenon lamp excitation. The dynamics of the Nd³⁺ excited states were characterized by decay times measurements and compared to earlier reported data for neodymium tungstates.     

Urbach’s rule of Bi4Ge3O12 doped with 3d and 4d ions

In this work, the influence of 3d (Fe, Mn) and 4d (Ru) ions on the absorption coefficient of the doped Bi₄Ge₃O₁₂ (BGO) in the spectral range 3.6-4.05 eV has been determined. The validity of Urbach’s rule is verified in an illuminated and an annealed state of the samples. The dependence between the incorporation of the different dopants and the values of their Urbach’s parameters is established. The creation and the destruction of the excitons, associated with the ionized donors, are explained. The Urbach’s energy of all samples is determined.     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.     

On the microscopic origin of the photochromic and photorefractive behavior of doped Bi4Ge3O12 single crystals

Doping Bi₄Ge₃O₁₂ single crystals with Co impurities enables the presence of a photochromic behavior which is induced at room temperature (rt) with ultraviolet (uv) light. As a consequence of the uv illumination a broad optical absorption from 1.0 to 4.1 eV is formed. This absorption is attributed to the creation and trapping of holes. The spectral efficiency of the damage and its thermal and optical stability have been characterized. Optically induced holographic gratings have been observed. They have been attributed mainly to a photorefractive effect. Some of those gratings exhibit a transient behavior that has been related to the simultaneous diffusion of electrons and holes. A microscopic model to account for the photochromic and photorefractive effects is discussed.     

Study on multiple near-infrared luminescent centers and effects of aluminum ions in Bi2O3-GeO2 glass system

We report on the near-infrared (NIR) luminescent properties of Bi₂O₃-GeO₂ glass. Apparent differences of NIR luminescence, decay properties and thermal stability manifest the co-existence of more than one active center in this system. The effects of Al ions introduced both unintentionally and intentionally were investigated. ²⁷Al NMR analysis proposes 4-fold Al coordination as dominant structure which can also provide the environment for active centers. We suggest that Al ions play a crucial role to restrain concentration quenching at higher Bi₂O₃ concentration instead of assisting to construct Bi centers.     

Synthesis and characterizations of Nd doped SrFe12O19 nanoparticles

This is the first report ever on Nd³⁺ doped M-type hexaferrite nanoparticles: SrNd_xFe_12−xO₁₉ (0 ≤ x ≤ 1) prepared by citrate precursor using the sol–gel technique followed by gel to crystallization. The influence of the Nd³⁺ substitution, Fe³⁺/Sr²⁺ molar ratio and the calcination temperature on the crystallization of ferrite phase have been examined using powder X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), inductance capacitance resistance meter bridge (LCR) and vibrating sample magnetometer (VSM). The structural analysis reveals that the Nd³⁺ ions rearrange themselves in the host lattice without disturbing the parent lattice and Fe³⁺/Sr²⁺ molar ratio less than 12 is more favorable to achieve single phase hexaferrite at calcination temperature 900 °C for 4 h. Mid-IR analysis confirms that Nd³⁺ occupies the octahedral site. Detailed studies of electrical properties of prepared materials have been investigated in the frequency range 100–1000 Hz at room temperature by LCR meter and two probe technique. The result shows that the electrical properties strongly depend upon the frequency of applied field and dopant concentration. The magnetic measurements showing a considerable improvement in coercivity with the substitution of Nd³⁺ on iron sites, while the unsubstituted hexaferrites have highest value of specific saturation magnetization.     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.