一种用于帧频提升系统的运动估计算法

基于静止检测、运动矢量预测,结合局部全搜索和下采样方法,提出一种有效的运动估计算法。将该算法用于基于运动估计运动补偿的帧频提升系统中。实验结果表明,该算法在减少计算量的同时,保证了内插帧有较高的主客观质量,能减少搜索点数,同时保持较高的搜索准确度。     

Improved photon management in a photoelectrochemical cell with Nd-modified TiO2 thin film photoanode

Photon management involving particularly an up-conversion process is proposed as a relatively novel strategy for improving the efficiency of hydrogen generation in photoelectrochemical cells (PEC) with wide-band gap photoanodes. Optically active photoanode has been constructed by electrodeposition of titanium dioxide nanopowders containing Nd³⁺ ions, synthesized via a sol-gel method, onto ITO/TiO₂(thin film) substrates. Thin films of TiO₂ have been deposited by means of RF magnetron sputtering in an ultra-high-vacuum system. X-ray diffraction, scanning electron microscopy, UV-VIS-NIR spectrophotometry, and photoluminescence have been applied to assess the properties of photoanodes. In experiments involving photon-assisted water splitting, an external up-converter containing Yb³⁺/Er³⁺ rare-earth ions has been used. Photocurrent as a function of voltage (V_B) under illumination with white light is relatively high (280 μA at V_B = 0 V) for pure TiO₂ thin films and it is not affected by the electrodeposition of TiO₂:Nd³⁺ powders. NIR-driven up-conversion with laser excitation at λ = 980 nm has been found responsible for a 13-fold increase in photocurrent at V_B = 0 V in the modified PEC configuration.     

Fabrication and comprehensive structural and spectroscopic properties of Er:Y2O3 transparent ceramics

Transparent Er:Y₂O₃ ceramics with sub-micron grain size (<1 μm) were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. The transmission of the undoped Y₂O₃ reaches 83%. The structural characteristics including the phonon energy were investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM) measurement. The overall spectroscopic properties of transmission, fluorescence emission up to 3000 nm, lifetime, up-conversion luminescence, and refractive index were systematically studied for both 0.25 at% and 7.0 at% Er:Y₂O₃ ceramics with different thicknesses. The comparison of the spectra of the fluorescence emission and up-conversion luminescence under both 976 and 808 nm laser excitation was performed. The multiple high-energy-state transitional processes after the excited state absorption (ESA) processes involved in the up-conversion are discriminated between the multi-phonon non-radiative transitions and the radiative transitions according to the measured maximum phonon vibrational energy. The calculation was performed based on the Judd–Ofelt theory.     

Er3+/Yb3+ co-doped bioactive glasses with up-conversion luminescence prepared by containerless processing

Er³⁺/Yb³⁺ co-doped bioactive glasses were prepared via containerless processing in an aerodynamic levitation furnace. The as-prepared glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDX). The up-conversion luminescence of as-prepared glasses was measured using an Omni- 3007 spectrometer. Furthermore, the in vitro bioactivity was evaluated by soaking the materials in simulated body fluid, and the biocompatibility was evaluated in MC3T3-E1 cell culture.The results show that containerless processing is a unique method to prepare homogeneous rare earth doped bioactive glasses. The obtained Er³⁺/Yb³⁺ co-doped glasses show green and red up-conversion luminescence at the excitation of 980 nm laser. The XRD analysis confirmed that calcium silicate powders, as starting materials, were completely transformed from the original multi-crystalline phase (CS-P) into the amorphous-glassy phase (CS-G, EYS, LCS) via containerless processing. The SEM observation combined with EDX and FTIR analyses showed that the as-prepared glasses were bioactive. The cell proliferation assay also revealed that the as-prepared glasses were biocompatible and nontoxic to MC3T3-E1 cells. This study suggests that the luminescent bioactive glasses prepared by containerless processing could be used for studying biodegradation of bone implantation materials.     

Energy transfer and luminescent properties of Tb3+ and Tb3+, Yb3+ doped CNGG phosphors

In this work,calcium niobium gallium garnet(Ca₃ Nb_1.6875Ga_3.1875O₁₂-CNGG) ceramic samples singledoped with Tb³⁺ and co-doped with Tb³⁺ and Yb³⁺ ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb³⁺ ions corresponding to the maximum luminescence in the green spectral range in CNGG:...     

Up-conversion processes in NaLaF4:Er

Structural and spectroscopic investigation of NaLaF₄:Er³⁺ material at different doping concentrations is presented. X-ray diffraction patterns, up-conversion luminescence spectra and decay curves for ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 optical transitions in the material are shown and possible excitation routes are discussed. Raman spectrum for the undoped material is presented and the effective phonon energy of the material is estimated. Based on the obtained results application of rare-earth doped NaLaF₄ in the field of up-conversion phosphors is evaluated.     

Bright upconversion emission of Nd in LiLa1−xNdxP4O12 nanocrystalline powders

Upconversion emission of Nd³⁺ doped LiLa_1−xNd_xP₄O₁₂ nanocrystals powders upon irradiation with 808 nm laser diode has been investigated. This emission of bright orange color was dependent on concentration and excitation incident light intensity. It was found that this emission was threshold phenomenon characterized by long build-up times which were dependent on energy of upconversion emission, concentration of active ions, size of nanocrystalline grains and power of incident light. The mechanism of observed upconversion was discussed in terms of thermally stimulated avalanche process. The emission intensity bistability of upconversion emission was demonstrated.     

Modification of twin crystal Cd0.5Zn0.5S photocatalyst with up-conversion nanoparticles for efficient photocatalytic H2-production

The photocatalytic H₂-production by solar light has been considered a promising technology to converse solar energy into carbon-free hydrogen. The development of efficient and stable catalysts is the most urgent problem in this technology. Up to now, twin crystal Cd_0.5Zn_0.5S solid solution has been regarded as the best efficient pristine sulphide catalysts for visible-light-driven hydrogen production. Its catalytic activity can be remarkably improved further by loading suitable co-catalyst, such as PdP_~0.33S_~1.67, noble metal Pt, and NiS_x. However, these twin crystal Cd_0.5Zn_0.5S-based nanocomposites can only response to partial (wavelength less than 520 nm) visible light irradiation. Large amount of visible light and near infrared light (NIR) in solar spectrum can not be absorbed by Cd_0.5Zn_0.5S and, therefore, do not contribute to the H₂ production. In this work, β-NaYF₄:Yb³⁺,Tm³⁺,Er³⁺ up-conversion nanoparticles (UPNs) are prepared by a hydrothermal process and the corresponding nanocomposite photocatalyst (twin crystal Cd_0.5Zn_0.5S/β-NaYF₄:Yb³⁺,Tm³⁺,Er³⁺ (T-CZS/UPNs)) based on this kind of up-conversion nanoparticles and twin crystal Cd_0.5Zn_0.5S nanocrystal is successfully prepared for the first time. The compositions, morphologies, and optical properties of the T-CZS/UPNs are investigated using XRD, SEM, HRTEM, UV–vis–NIR absorption spectra and photoluminescence (PL) spectrum. The photocatalytic hydrogen evolution experiments are performed under the irradiation of visible light, NIR light or simulated solar light, respectively. The H₂ production rate over T-CZS/UPNs-15 nanocomposite under the irradiation of simulated solar light in the presence of Na₂S/Na₂SO₃ as sacrificial agent is measured to be 159.3 mmol/h/g, which is 3.4 times higher than that of pristine T-CZS nanocrystals. In particular, this nanocomposite exhibits also significant photocatalytic hydrogen production rate (0.497 mmol/g/h) under NIR light irradiation (λ > 800 nm), reveals the contribution of NIR light to H₂ production via an photon-up-conversion process. This work gives an innovative vision in constructing efficient photocatalysts to make the efficient use of NIR solar light.     

Bioactivity and up-conversion luminescence characteristics of Yb3+/Tb3+ co-doped bioglass system

The present study elaborates the bioactive and optical features of Yb³⁺/Tb³⁺ co-doped bio-active glass. Three different combinations with assorted elemental concentrations were investigated. The amorphous nature of bioglass devoid of crystalline phases until 700 °C has been confirmed through XRD analysis. The results from Raman and FT-IR accomplished the presence of Si–O–Si broad vibrational modes typical of amorphous glass and further the characteristic PO₄ vibrations were also confirmed. The up-conversion luminescence studies revealed the typical Tb³⁺ emission excited at 976 nm. The mechanism that involved in the up-conversion and energy transfer emission phenomena were discussed. Morphological features of SBF immersed specimen affirm the formation of apatite layer by the spherical spongy agglomerates observed over the surface.