Nature of intrinsic luminescence in the glasses of CaO–Ga2O3–GeO2 system

The intrinsic luminescence of glasses of the CaO–Ga₂O₃–GeO₂ system has been investigated. High chemical purity and optical quality glasses, both undoped and doped with transition and rare-earth ions with different compositions, were obtained by high-temperature synthesis. The influences of the basic glass composition, impurities (Cr³⁺, Mn²⁺, Eu²⁺, Nd³⁺, Ho³⁺, Er³⁺, and Ce³⁺) and different kinds of excitation, on the intrinsic luminescence of the CaO–Ga₂O₃–GeO₂ glasses were investigated. The nature and possible mechanisms of the intrinsic luminescence in glasses of this system are discussed. The proposed models of intrinsic luminescence are supported by electron spin resonance spectroscopy.     

Enhanced luminescence from transparent Ni-doped MgO–Al2O3–SiO2 glass ceramics by Ga2O3 addition

Transparent Ni²⁺-doped MgO–Al₂O₃–SiO₂ glass ceramics without and with Ga₂O₃ were synthetized. The precipitation of spinel nanocrystals, which was identified as solid solutions in the glass ceramics, could be favored by Ga₂O₃ addition and their sizes were about 7.6 nm in diameter. The luminescent intensity of the Ni²⁺-doped glass ceramics was largely enhanced by Ga₂O₃ addition which could mainly be caused by increasing of Ni²⁺ in the octahedral sites and the reduction of the mean frequency of phonon density of states in the spinel nanocrystals of solid solutions. The full width at half maximum (FWHM) of emissions for the glass ceramics with different Ga₂O₃ content was all more than 200 nm. The emission lifetime increased with the Ga₂O₃ content and the longest lifetime is about 250 μs. The Ni²⁺-doped transparent glass ceramics with Ga₂O₃ addition have potential application as broadband optical amplifier and laser materials.     

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Ceramics with formula (1 − x)Pb(Zr_0.52Ti_0.48)O₃–x(Bi_3.25La_0.75)Ti₃O₁₂ (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.     

Optical and electrical properties of binary WO3–Pb3O4 glasses

A glass system of the composition xWO₃+(100−x)Pb₃O₄, with x=5, 10, 20 and 30 mol.% was prepared. The optical absorption, ac and dc conductivities are the subject of the present work. The optical absorption indicates that the electronic transition is indirect and is associated with phonon assisted transition. The exponential dependence of the absorption coefficient as a function of the incident photon energy suggests that the Urbach rule is obeyed, and indicates the formation of a band tail. On the other hand, ac conductivity measurements are performed in the frequency range 0.1–100 kHz, and in the temperature range 300–600 K. The results of the electrical conductivity are discussed on the basis of electronic glass conduction models. Correlated narrow-band limit for random sites and single polaron hopping model are found to describe the experimental results effectively. The dielectric constant was correlated to the optical band gap and a satisfactory relation was found. It was also possible to calculate the thermochromic properties from independent ac and dc measurements, and it was possible to evaluate the optical gap at 0 K by extrapolation.     

Correlation among electronic polarizability, optical basicity and interaction parameter of Bi2O3–B2O3 glasses

For optical basicity and electronic polarizability, the previous studies basically concentrate on the wavelength range of the visible light region. However, heavy metal oxides glasses have a reputation of being good materials for infrared region. In this study, new data of the average electronic polarizability of the oxide ion _O^2-, optical basicity Λ and Yamashita–Kurosawa's interaction parameter A of Bi₂O₃–B₂O₃ glasses have been calculated in a wavelength range from 404.66 to 1083.03 nm. The present investigation suggests that both _O^2- and Λ increase gradually with increasing wave number, and A decreases with increasing wave number. Furthermore, close correlations are studied among _O^2-, Λ, A and refractive index n in this paper. Particularly, it has been found that a quantitative relationship between electronic polarizability and optical basicity is observed in a wavelength range from 404.66 to 1083.03 nm. Our present study extends over a wide range of _O^2-, Λ and A values.     

Luminescence enhancement in (Nd+Ce) doped SiO2 : Al2O3 sol–gel glasses

An enhancement in NIR luminescence from Nd³⁺-doped Ce³⁺ co-doped SiO₂+Al₂O₃ sol–gel glasses has been observed. The lasing transition (⁴F_3/2→⁴I_11/2) at 1072 nm from the dual rare-earth Nd³⁺+Ce³⁺-doped glasses has shown an emission strength of about five times that of the single rare-earth ion Nd³⁺-doped glass. From the measurement of lifetimes of the transition at 1072 nm, the transfer rate (W_tr), critical distance (R₀) and energy transfer efficiency (η) of the neodymium glasses have been calculated.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Structure of Na2O·MO·SiO2·CaF2 (M=Mg,Ca) oxyfluoride glasses

(9−x)CaO·xMgO·15Na₂O·60SiO₂·16CaF₂(x=0, 2, 4, 6, and 9) oxyfluoride glasses were prepared. Utilizing the Raman scattering technique together with ²⁹Si and ¹⁹F MAS NMR, the effect of alkaline metal oxides on the Q species of glass was characterized. Raman results show that as magnesia is added at the expense of calcium oxide, the disproportional reaction Q³→Q⁴+Q² (Qⁿ is a SiO₄ tetrahedron with n bridging oxygens) prompted due to the high ionic field strength of magnesia, magnesium oxide entered into the silicate network as tetrahedral MgO₄, and removed other modifying ions for charge compensation. This reaction was confirmed by ²⁹Si MAS NMR. ¹⁹F MAS NMR results show that fluorine exists in the form of mixed calcium sodium fluoride species in all glasses and no Si–F bonds were formed. As CaO is gradually replaced by MgO (x=6, 9), a proportion of the magnesium ions combines with fluorine to form the MgF⁺ species. Meanwhile, some part of Na⁺ ions complex F⁻ in the form of F–Na(6).     

PbO–Bi2O3–Ga2O3–BaO glasses doped by Er as novel materials for IR emission

Infra-red luminescence (at wavelengths about 1600 and 2500 nm) from Er³⁺ ions embedded in PbO–Bi₂O₃–Ga₂O₃–BaO glass hosts is reported for room and helium liquid temperatures. The substantial influence of energy transfer processes between the host and Er³⁺ ions is shown experimentally through the dependences of photoluminescence on light polarization and excitation wavelength. Only the application of the polarized pumping YAG–Nd laser beam (λ=1060 nm) stimulates substantial luminescence with quantum efficiency up to 24%. The role of phonon-relaxation subsystem in the observed luminescence is discussed.     

Structural characterization of the sol–gel oxide powders from the ZnO–TiO2–SiO2 system

This work is a study that deals with the synthesis by the sol–gel method and the structural characterization of the oxide powders belonging to the ternary system ZnO–TiO₂–SiO₂ (ZTS). The sol–gel synthesis starts from inorganic precursors, which have been processed under the variation of different technological parameters. We have investigated the dependence of the gelling time on pH and on the temperature of synthesis as well as on water and ammonia amounts. In the case of ZTS samples, the shortest gelling duration appears for low pH values when ZnO content is increased and at small ammonia concentrations when the ZnO content is decreased, respectively. On the contrary, ZTS samples containing high amounts of TiO₂ provide evidence of a short gelling time for high pH and large ammonia amounts. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy provided structural information on these ternary oxide powders. These analyses revealed that relative high amounts of ZnO yields in a change from octahedral [ ZnO₆] units to tetrahedral [ ZnO₄] units in the powder structure. Optical phonons specific for SiO₂ and TiO₂ in both octahedral and tetrahedral groups are shown. High thermal and chemical stability was put in evidence by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) in the 20–1000 C temperature range.     

Radiation induced paramagnetic centres in MgOAl2O3SiO2 glasses containing TiO2

Upon irradiation with ⁶⁰Co γ-rays Cordierite glasses with added TiO₂ display two dominant ESR resonances arising from (a) Ti³⁺ ions (b) holes trapped at non-bridging oxygen ions singly bonded to [SiO₄]^? tetrahedra. The Ti³⁺ ions appear to be in D_4h octahedral sites with the evident distributions between the principal g values arising from an isotropic randomness at the titanium sites. However, the g parameter distributions of the hole resonance, and their changes during the addition of TiO₂ indicate the development of Silicate structures in the glasses which are the precursors of the major low temperature crystalline phases. The invariance of the hole and electron resonance lines with pre-crystallization heat treatments indicates that neither the titanium associated structures or the basic silicate structure of the glass are changed by such treatments.     

Fixed charge and interface traps at heterovalent interfaces between Si(1 0 0) and non-crystalline Al2O3–Ta2O5 alloys

Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta₂O₅)_x(Al₂O₃)_1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta₂O₅ and Al₂O₃. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta₂O₅ with respect to Si.     

Photo-operated two-photon absorption effects in the GeSe2–Ga2S3–PbI2 glasses

The possibility to operate the two-photon absorption (TPA) of newly synthesized GeSe₂–Ga₂S₃–PbI₂ glasses using the CO laser beam (λ=5.5 μm) as a photoinducing one has been demonstrated. As the fundamental laser beam we have used the illumination of 10.6 μm passively modulated 0.5 ns CO₂ laser with a rate repetition of about 10 Hz. We have established that the maximal photoinduced TPA is observed for the 8% doped samples (up to 14 cm/GW), which is achieved at a pump CO laser pump power density equal to about 0.6 GW/cm². The undoped PbI₂ samples show the TPA maximum at a pump power density of about 0.2 cm/GW. The minimal TPA values were observed for the samples with 5% of PbI₂. The obtained results show that these materials can be used as effective optically operated optical limiters.     

Thermodynamic modeling of the ZrO2–YO1.5 system

In the present work, an optimized set of Gibbs energy functions is proposed for the Y–Zr–O ternary system. We focus on the ZrO₂–YO_1.5 quasi-binary system, but reoptimizations of the Zr–O and Y–O binary systems are included as well. The parameters for the Y–Zr binary system were taken from a previous assessment.

The ZrO₂–YO_1.5 system was treated as a quasi-binary section of the Y–Zr–O ternary system. The existing experimental data on the ZrO₂–YO_1.5 system were carefully reviewed. The related parameters were optimized using both thermodynamic data and phase diagram data. A calculated phase diagram of the ZrO₂–YO_1.5 system is presented. Our optimization agrees well with most experimental data. Two calculated isothermal sections of the Y–Zr–O system at 1500 and 2000 K are also included.     

Electric conductivity and relaxation in ZnF2–AlF3–PbF2–LiF glasses

The electric conductivity of ZnF₂–AlF₃–PbF₂–LiF glasses has been studied in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F⁻ ions by Li⁺ ions. Small values of the stretching exponent β are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.     

Effect of BiFeO3 addition on Bi2O3–ZnO–Nb2O5 based ceramics

In this paper, low temperature sintering of the Bi₂(Zn_1/3Nb_2/3)₂O₇ (β-BZN) dielectric ceramics was studied with the use of BiFeO₃ as a sintering aid. The effects of BiFeO₃ contents and the sintering temperature on the phase structure, density and dielectric properties were investigated. The results showed that the sintering temperature could be decreased and the dielectric properties could be retained by the addition of BiFeO₃. The structure of BiFeO₃ doped β-BZN was still the monoclinic pyrochlore phase. The sintering temperature of BiFeO₃ doped β-BZN ceramics was reduced from 1000 °C to 920 °C. In the case of 0.15 wt.% BiFeO₃ addition, the β-BZN ceramics sintered at 920 °C exhibited good dielectric properties, which were listed as follows: ε_r = 79 and tan δ = 0.00086 at a frequency of 1 MHz. The obtained properties make this composition to be a good candidate for the LTCC application.     

Modification in structural and optical properties of ZnO, CeO2 doped Al2O3-PbO-B2O3 glasses

The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV visible spectroscopic measurement techniques. XRD results have confirmed the glassy nature of the samples. The FTIR spectral analysis reveals that with the combined presence of ZnO and CeO₂ contents in Al₂O₃-PbO-B₂O₃ glasses, more BO₃ groups are transformed into BO₄. The optical analysis reveals that optical band gap energy decreases more for CeO₂-ZnO-Al₂O₃-PbO-B₂O₃ glasses (from 2.28 to 1.84 eV). The presence of CeO₂ and ZnO in the glass samples causes more compaction of the borate network due to the formation of more BO₄ groups and the presence of ZnO₄ groups, which results an increase in density, refractive index and decrease of molar volume.     

稀土离子(Eu3+,Tb3+,Ce3+)掺杂ZnAl2O4/SiO2微晶玻璃的制备与发光性能

采用凝胶法分别制备出4.5ZnO-5.5Al₂O₃-90SiO₂(ZAS)以及ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce) 透明微晶玻璃。利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和荧光光谱仪(PL)等测试手段,研究了稀土离子掺杂浓度对ZAS微晶玻璃的结构和发光性能的影响。XRD结果表明,ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce)微晶玻璃包含ZnAl₂O₄晶相和SiO₂非晶相,ZnAl₂O₄平均晶粒尺寸约为30 nm,稀土离子的掺杂没有显著改变原来的ZnAl₂O₄晶体结构。TEM结果表明,900 ℃时ZnAl₂O₄从ZAS体系中析出。PL光谱显示,Eu³⁺ 存在 ⁵D₀→⁷F₂跃迁,ZAS[DK]:Eu³⁺在611 nm 处发出强烈的红色光;由于Tb³⁺ 的⁵D₄→⁷F₅ 跃迁,ZAS[DK]:Tb³⁺在541 nm 处发出明亮的绿色光;ZAS[DK]:Ce³⁺ 在381 nm处显示了蓝光发射,对应于Ce³⁺ 的5d→4f 轨道跃迁。ZAS[DK]:RE³⁺ (RE=Eu, Tb, Ce)的PL发射光谱存在着浓度猝灭现象,Eu³⁺、Tb³⁺ 和Ce³⁺的最佳单掺杂摩尔分数分别为20%、20%和3%。CIE色度图表明,ZAS[DK]: RE³⁺ (RE=Eu,Tb,Ce)的色坐标分别位于红光、绿光和蓝光区域。实验结果表明,ZAS:RE³⁺ (RE=Eu,Tb,Ce) 微晶玻璃是一种良好的可用于全色显示的白光LED材料。     

Dynamical heterogeneity and diffusion in high-density Al2O3·2SiO2 melts

Dynamical heterogeneity (DH) in high-density Al₂O₃·2SiO₂ melts has been studied in a model containing 3025 atoms via molecular dynamics (MD) simulation and at the fixed density of 4.0 g/cm³. Non-Gaussian parameter of atomic species in the system has been found and discussed. We found a clear evidence of the existence of DH in high-density Al₂O₃·2SiO₂, which has specific features differed from those observed in the lower-density one. The most mobile and immobile atoms in the system have a tendency to form clusters and temperature dependence of their mean cluster size was found. On the other hand, diffusion constant of atomic species in the system has been calculated at temperatures ranged from 3150 to 7000 K. Calculations show that at relatively not high temperatures, temperature dependence of diffusion constant shows an Arrhenius law and at higher temperatures it shows a power law: D∝(T−T_C)^γ. Diffusion data of high-density melts have been compared with those for the low-density ones. Diffusion mechanism in the system has been discussed via the temperature dependence of diffusion constant ratio and activation energy. And we found the existence of cooperative diffusion mechanism in the system.     

Mg，Ti共掺Al2O3透明多晶陶瓷光谱性能研究

采用传统无压烧结工艺制备Mg，Ti共掺透明氧化铝陶瓷，测定了其吸收光谱、荧光光谱和激发光谱，结果表明，由于Mg²⁺的电荷补偿，当Ti掺入量较小时，Ti主要以Ti⁴⁺形式存在，(Mg，Ti):Al₂O₃透明陶瓷只在250nm的紫外波段有吸收峰，为O^2-→Ti⁴⁺的电荷转移跃迁产生的吸收，并产生Ti⁴⁺离子在280—290nm和410—420nm的荧光发射峰