Time-resolved luminescence of UO2MoO4

Time-resolved spectroscopy and decay-time measurements for the intrinsic and trap emission lines of UO₂MoO₄ supply experimental evidence for fast energy migration among intrinsic centres and from intrinsic to trap centres. The temperature behaviour of the decay time for the main trap lines reveals an energy transfer rate from trap to intrinsic centres in the order of 5×10⁹s^-1, while the transfer rate among intrinsic centres, as estimated from the correlation field splitting, is 3×10¹¹ s^-1.     

Preparation of amorphous films of superionic conducting glasses in systems AgIAg2MoO4 and AgIAg2OB2O3

Thermal evaporation, flash evaporation and rf-sputtering techniques were applied to the preparation of amorphous films of superionic conducting glasses in the systems AgIAg₂MoO₄ and AgIAg₂OB₂O₃. The flash-evaporated films were amorphous and showed very high conductivities, about 2 × 10^?2S/cm for the AgIAg₂MoO₄ and about 5 × 10^?3S/cm for the AgIAg₂OB₂O₃ at room temperature, and gave a Ag⁺ transport number of unity. The thermal evaporation method produced crystalline-phase included films. The rf-sputtered films were amorphous by X-ray diffraction and the transport number of Ag⁺ ions was smaller than unity (about 0.9). Thus flash evaporation was concluded to be the most suitable method for preparing amorphous films of superionic conducting glasses.     

Investigation of the luminescence spectrum of UO2MoO4

By time-resolved spectroscopy the intrinsic emission spectrum of UO₂MoO₄ at 4.2 K is obtained. The main progressions in the vibronic structure are identified as couplings with the A_g correlation field components of the symmetric and asymmetric UO₂ stretching modes. The intrinsic zero-phonon line in the emission and excitation spectrum is shown to be split both by the crystal field and correlation field. The steady-state emission spectrum at 4.2 K is dominated by emission from traps. The vibronic structure of the trap emission reveals that all traps are distorted uranyl groups.     

The thermoelectric power of charge-density-wave conductors Rb0.3MoO3 and Rb0.15K0.15MoO3

The thermoelectric power (TEP) of the quasi-one-dimensional charge-density-wave (CDW) conductors rubidium blue bronze Rb_0.3MoO₃ and its alloy Rb_0.15K_0.15MoO₃ were measured in the temperature range 80-280 K. The result showed a sign change from a small positive value to a great negative value where the Peierls transition temperatures (T_p) are 183 and 180 K for Rb_0.3MoO₃ and Rb_0.15K_0.15MoO₃, respectively. Above T_p, the TEP for both samples can be described with the empirical relation S=AT+B; while below T_p, the TEP fits well the relation S=AT+B/T based on the experimental data. The Fermi energies ε_F for Rb_0.3MoO₃ and Rb_0.15K_0.15MoO₃ are estimated to be 1.55 and 0.53 eV, respectively.     

K0.3MoO3和Tl0.3MoO3派尔斯相变临界行为的比热研究

采用连续绝热加热法测量了K_0.3MoO₃和Tl_0.3MoO₃在100—220K温度范围内的比热。发现K_0.3MoO₃和Tl_0.3MoO₃分别在177.5K和172.3K发生派尔斯相变。对派尔斯相变附近比热临界行为的研究表明,K_0.3MoO₃和Tl_0.3MoO₃的临界区域宽度分别为6K和8K,临界行为属于三维XY模型普适类。 关键词：     

Pool-Frenkel effect and high frequency dielectric constant determination of semiconducting P2O5-Li2MoO4-Li2O and P2O5-Na2MoO4-Na2O bulk glasses

The ternary 70P₂O₅-10Li₂MoO₄-20Li₂O and 70P₂O₅-10Na₂MoO₄-20Na₂O glasses, prepared by the press-melt quenching technique, were studied at temperatures between 298 and 418 K for their high dc electric field properties. For the above purpose, the effect of a strong electric field on the dc conduction of these amorphous bulk samples was investigated using the gap-type electrode configuration. At low electric fields, the current-voltage (I — V) characteristics have a linear shape, while at high electric fields (> 10³ V/cm), bulk samples show nonlinear effects (nonohmic conduction). Current-voltage curves show increasing departure from Ohm’s law with increasing current density, leading to critical phenomena at a maximum voltage (threshold voltage), known as switching (switch from a low-conduction state to a higher-conduction state at threshold voltage). The Pool-Frenkel high-field effect was observed at electrical fields of about 10³–10⁴ V/cm; then the lowering factor of the potential barrier, the high frequency dielectric constant, and the refractive index of these glasses were determined.      

Dielectric dispersion in PbO-Sb2O3-As2O3:V2O5 glasses

Dielectric properties, viz. dielectric constant ε′, loss tan δ and a.c conductivity σ_ac (over a wide range of frequency and temperature) and dielectric breakdown strength of PbO-Sb₂O₃-As₂O₃ glasses doped with V₂O₅ (ranging from 0 to 0.5 mol%) are studied. Analysis of these results, based on optical absorption and ESR spectra, indicates that the insulating strength of the glasses is comparatively high when the concentration of V₂O₅ is about 0.3 mol% in the glass matrix.     

三元异质结构Ag-Bi2MoO6/BiPO4光催化剂高效降解苯酚红

多组分复合体系有利于电荷的有效分离,减少电子空穴对的复合几率。通过低温液相法首次合成Ag-Bi₂MoO₆/BiPO₄三元异质结构光催化剂。利用XRD、SEM、EDX及XPS等技术对样品进行了表征。结果表明,Ag纳米粒子光照积累在Bi₂MoO₆/BiPO₄的表面,通过表面等离子共振增加对可见光的吸收,同时作为电子受体促进了光生电子的转移。Ag、BiPO₄和Bi₂MoO₆形成三元异质结构有效地抑制了光生电子空穴对的复合。Ag-Bi₂MoO₆/BiPO₄表现出优异的光催化性能,其光催化活性较BiPO₄、Bi₂MoO₆和Bi₂MoO₆/BiPO₄样品有较大提高。并且对Ag-Bi₂MoO₆/BiPO₄三元异质结构的光催化机制进行了讨论。光催化过程中反应活性物种捕获实验结果表明h⁺和O₂^·-是主要的活性基团.     

Optical properties of Er in MoO3-Bi2O3-TeO2 glasses

Erbium-doped MoO₃−Bi₂O₃−TeO₂ (MBT) glasses suitable for broadband optical amplifier applications have been fabricated and characterized optically. The maximum phonon band of undoped glasses is at 915 cm⁻¹, and the emission from the Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition locates around 1.53 μm with a full width at half maximum (FWHM) of ∼80 nm. The lifetime and quantum efficiency of the ⁴I_13/2 level are 2.13 ms and ∼90%, respectively. Under the same measurement condition, the upconversion emission intensities at 550 nm in Er³⁺-doped MBT glasses is about 30 times weaker than that in Er³⁺-doped Na₂O−ZnO−TeO₂ (NZT) glasses.     

Sol-gel growth of Gd2MoO6:Eu nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6:Eu) and their luminescent properties

SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors. The XRD results demonstrate that the Gd₂MoO₆:Eu³⁺ layers on the SiO₂ spheres begin to crystallize after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd₂MoO₆:Eu³⁺ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu³⁺ shows a strong PL luminescence (dominated by ⁵D₀-⁷F₂ red emission at 613 nm) under the excitation of 307 nm UV light. The PL intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles.     

Fluoride glasses in the InF3-GaF3-YF3-PbF2-CaF2-ZnF2 system

New glasses have been synthesized in a multicomponent system based on indium fluoride. Samples of a few mm in thickness were obtained. They are transparent and homogeneous. Main physical properties such as density, characteristic temperatures, density, thermal expansion and refractive index have been measured. The evolution versus composition is reported for samples with the formula: (35−x) InF₃-xGaF₃-10YF₃-25PbF₂-15CaF₂-15ZnF₂. T_g lies between 260 and 296 °C while melting starts around 480 °C. Glass samples are stable at room temperature. By comparison with other standard fluoride glasses, they exhibit higher refractive index and density.     

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.     

Effect of cation substitution in fluorine-oxygen molybdates (NH4)2 ? xAxMoO2F4

Thermophysical and structural studies of (NH₄)_{2 − x} A _x MoO₂F₄ (A = Cs, Rb, K) solid solutions of oxyfluorides have been performed. The character of the influence of cation substitutions on the stability of the initial phase (space group Cmcm) and on the mechanism of phase transitions has been elucidated.     

Role of WO3 in structural and optical properties of WO3-Al2O3-PbO-B2O3 glasses

Glass samples of composition xAl₂O₃-20PbO-(80−x)B₂O₃ and xWO₃-xAl₂O₃-20PbO-(80−2x)B₂O₃ with x varying from 0% to 10% mole fraction are prepared by melt quench technique. The optical band gap decreases (from 3.21 to 2.37 eV) more for WO₃-Al₂O₃-PbO-B₂O₃ glasses with an addition of WO₃ content. The FTIR spectral studies have pointed out the conversion of structural units of BO₃ to BO₄ and WO₄ to WO₆ in these glasses. The increase in density from 4.51 to 5.80 g cm⁻³ for WO₃-Al₂O₃-PbO-B₂O₃ glasses is observed with an increase in WO₃ content. This is observed that the atomic structure changes more with the incorporation of WO₃. This is due to the formation of WO₆, WO₄ and BO₄ units.     

Semiconduction in xFe2O3.(1-x) [3B2O3.PbO] glasses

The electrical resistivity of iron lead borate glasses was measured over the temperature range 300–700 K. The resistivity increases with the iron content and is a function of the Fe²⁺/Fe_tot ratio, but the minimum does not appear for 0.28 ≤ c ≤ 0.50. The samples with x > 15 mol % Fe₂O₃ show the presence of two activation energies for conduction. A change in the activation energy can be explained by charge transfer between iron ions in similar positions at low temperatures, and between iron ions in different positions at higher temperatures. In order to analyse the conductivity data, we have considered in all the glasses a polaronic model for conduction.     

On the iron valence states in B2O3-PbO-GeO2 glasses

The Mössbauer effect measurements performed on 20Fe₂O₃ 80 3B₂O₃ (1?x)PbO xGeO₂ glasses show that the ratio between the number of ferrous ions to the total number of iron ions decreases by increasing the GeO₂ content. The Curie constants calculated from the distribution of iron cations obtained by Mössbauer effect data are in agreement with the values determined from magnetic measurements. Finally, we discuss the influence of the glass composition and melting temperature on the iron valence states.     

Structural and optical properties of WO3-ZnO-PbO-B2O3 glasses

Glass samples of compositions 20PbO-80B₂O₃ and xWO₃—(20−x) ZnO-20PbO-60B₂O₃ with x varying from 0% to 10% mole fraction are prepared by the melt quench technique. Decrease in the band gap from 2.86 to 2.16 eV for ZnO-PbO-B₂O₃ glasses with an increase in the WO₃ content has been observed and discussed. The FTIR spectral studies have pointed out the conversion of structural units of BO₃ to BO₄ and WO₄ to WO₆ with the presence of W-O-W vibration of tungsten and incorporation of ZnO₄ structural units of zinc in these glasses. The increase in density from 2.75 to 4.03 gcm⁻³ for ZnO-PbO-B₂O₃ glasses is observed with an increase in WO₃ content. Due to the formation of WO₆, WO₄ and BO₄ units, changes in the atomic structure with WO₃ composition are observed and discussed.     

Nonplanar domain walls in ferroelastic Gd2(MoO4)3 and Pb3(PO4)2

A new stable, mobile zigzag-shaped domain wall configuration has been discovered in the Gd₂(MoO₄)₃ and Pb₃(PO₄)₂ structures. Previous work on these materials had not predicted this type of domain wall. The zigzag walls have mobilities 30–40 times that of planar walls in the same material. This increased mobility can be explained as a geometrical effect.     

Effect of WO3 on structural and optical properties of CeO2-PbO-B2O3 glasses

Pure and WO₃ doped CeO₂-PbO-B₂O₃ glasses are prepared by the melt-quench technique. The structural and optical analyses of glasses are carried out by XRD, FTIR, density and UV-vis spectroscopic measurement techniques. FTIR analysis indicates the transformation of structural units of BO₃ into BO₄ with W-O-W vibration and the presence of WO₄ and WO₆ units observed with increase in WO₃ contents. Decrease in band gap for CeO₂-PbO-B₂O₃ glasses from 2.89 to 2.30 eV and for WO₃ doped glasses from 2.89 to 1.95 eV has been observed and discussed. This decrease in band gap with WO₃ doping approaches to semiconductor behavior. It shows that the presence of WO₃ in the glass samples causes more compaction of the borate network due to the formation of BO₄ groups and the presence of WO₄ and WO₆ groups, which result in a decrease in the optical band gap energy and increase in the density.     

Optical properties of the red bronze K0.33MoO3

The optical reflectivity of the red bronze K_0.33MoO₃ has been measured on single crystals in the spectral energy range between 0.03 and 12 eV at temperatures from 4 K to 300 K using polarized light. The optical constants have been determined by means of a Kramers-Kronig analysis; the data are interpreted that this compound is a 0.5 eV energy gap semiconductor with very strong anisotropy in the infrared and visible energy range.