Optical properties of GdTaO4:Eu thick films prepared from a PVP-containing solution

Transparent GdTaO₄:Eu³⁺ thick films were prepared from the inorganic salt and 2-methoxyethanol solution containing polyvinylpyrrolidone (PVP) via sol-gel technique. The critical thickness of the film, i.e. the maximum thickness achievable without crack formation via non-repetitive deposition, was 0.8 μm. The effect of PVP on the morphology, crystallization behavior and optical property of the GdTaO₄:Eu³⁺ thick film was investigated. The results indicated that PVP could play an important role in the formation of transparent GdTaO₄:Eu³⁺ thick films, suppressing the stress evolution, adjusting the sol viscosity, ameliorating the crystallinity, and strengthening the covalency of Eu-O bonds. The GdTaO₄:Eu³⁺ thick films prepared with PVP exhibited a superior photoluminescence and X-ray exited luminescence, which implies that it will have promising applications in high-spatial-resolution X-ray imaging and flat panel display devices.     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.     

Magnetoelectric effect in laminates of polymer-based pseudo-1–3 (Tb0.3Dy0.7)0.5Pr0.5Fe1.55 composite and?0.3Pb(Mg1/3Nb2/3)O3–0.7PbTiO3 single crystal

We report an extrinsic magnetoelectric effect in composite laminates made by sandwiching one thickness-polarized 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) piezoelectric single crystal plate between two length-magnetized, polymer-based pseudo-1–3 (Tb_0.3Dy_0.7)_0.5Pr_0.5Fe_1.55 magnetostrictive composite plates. The laminates exhibit large magnetoelectric voltage coefficients (α _V ) of ∼0.17 V/Oe with a flat response for frequencies in excess of 40 kHz and of ∼2.97 V/Oe at the natural resonance frequency of ∼65 kHz. The distinct advantages of the laminates include high magnetic field sensitivity, low Joule heating loss, wide operating bandwidth, and low cost.     

电荷补偿对Sr2SiO4:Dy3+材料发射光谱的影响

采用高温固相反应方法在空气中制备了Sr2SiO4:Dy3+发光材料.在365 nm紫外光激发下,测得Sr2SiO4:Dy3+材料的发射光谱为一多峰宽谱,发射峰分别位于486,575和665 nm处.研究了电荷补偿剂Li+,Na+和K+对Sr2SiO4:Dy3+材料发射光谱强度的影响,结果显示,不同电荷补偿剂下,随电荷补偿剂掺杂浓度的增大,Sr2SiO4:Dy3+材料发射光谱强度的演化趋势相同,即,Sr2SiO4:Dy3+材料发射峰强度先增大后减小,但不同电荷补偿剂下,材料发射峰强度最大处对应的补偿剂浓度不同,对应Li,Na+和K+时,浓度分别为4 mol%,3 mol%和3 mol%.同时,对研究结果进行了理论分析.     

Enhanced piezoelectric properties of sodium bismuth titanate (Na0.5Bi4.5Ti4O15) ceramics with B‐site cobalt modification

The piezoelectric properties of the cobalt‐modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics were investigated. The piezoelectric properties of NBT ceramics were significantly enhanced by cobalt modification. The Curie temperature T_C and piezoelectric constant d₃₃ for the 0.3 wt% cobalt‐modified NBT ceramics (NBT‐C3) were found to be 663 °C and 30 pC/N, respectively. Thermal annealing studies presented that the cobalt‐modified NBT ceramics possess stable piezoelectric properties, demonstrating that the cobalt‐modified NBT‐based ceramics are promising candidates for high temperature piezoelectric applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hawking radiation of five-dimensional rotating black hole

Applying the Damour–Ruffini method, we have considered the Hawking radiation of the five-dimensional rotating black hole. When taking the energy conservation and angular momentum conservation into consideration and considering the reaction of the radiation of the particle to spacetime, we see that the exact radiation spectrum is not purely thermal and the angular momentum of the black hole is quantized.     

Electron swarm coefficients in 1,1,1,2 tetrafluoroethane (R134a) and its mixtures with Ar

Using a pulsed Townsend technique, we have measured the drift velocity, the longitudinal diffusion coefficient and the effective ionisation coefficient of electrons in R134a and R134a-Ar over a wide range of the density-reduced electric field intensity, E/N. Regarding the measurement of the electron drift velocities and of the effective ionization coefficients, we have covered a wider range than that hitherto achieved for pure R134a. Both the electron drift velocity and the effective ionisation coefficient have been found in very good agreement with those published in the literature, covering a shorter range of E/N. On the other hand, the swarm coefficients on R134a-Ar are, to the best of our knowledge, the first to be published. It is hoped that these data will be of interest for the test/derivation of electron collision cross sections for this important hydrofluorocarbon gas, which is nowadays of great use in gaseous detectors.     

LiMBO3 : Dy3+材料的发光特性

采用固相法制备了LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料,并研究了材料的发光特性。LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料的发射光谱均呈多峰发射,对应于Ca,Sr,Ba,其主发射峰分别是Dy³⁺的⁴F_9/2→⁶H_15/2(484,486,486 nm),⁶H_13/2(577,578,578 nm)和⁶H_11/2(668,668,666 nm)跃迁。监测黄色发射峰时,所得激发光 谱峰值位置相同,主激发峰分别为331,368, 397,433,462,478 nm,对应Dy³⁺的⁶H_15/2→ ⁴D_7/2,⁶P_7/2,⁶M_21/2,⁴G_11/2,⁴I_15/2和⁶F_9/2跃迁。研究了敏化剂Ce³⁺及电荷补偿剂Li⁺、Na⁺和K⁺对LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料发光强度的影响。结果显示:加入敏化剂Ce³⁺提高了材料的发光强度,发光强度最大处对应的Ce³⁺浓度为3%;加入电荷补偿剂Li⁺、Na⁺和K⁺后,材料的发光强度也得到了明显提高,但发光强度最大处对应的Li⁺、Na⁺和K⁺浓度不同,依次为4%、4%和3%。     

Statistical-Mechanical Entropy of a Black Hole with a Global Monopole to All Orders in Planck Length

Considering corrections to all orders in the Planck length on the quantum state density from the generalized uncertainty principle, we calculate the statistical entropy of the scalar field in the global monopole black hole spacetime without any artificial cutoff. It is shown that the entropy is proportional to the horizon area.     

Hawking radiation as tunneling and the unified first law of thermodynamics at the apparent horizon of the FRW universe

Relations between the tunneling rate FRW universe are investigated. The namics in such a dynamical system. first law of thermodynamics through and the unified first law of thermodynamics at the apparent horizon of the tunneling rate arises as a consequence of the unified first law of thermodyAnalysis shows how the tunneling is intimately connected with the unified the principle of conservation of energy.