查看更多>>摘要：Over the years, phosphor-converted white light-emitting diodes (pc-WLEDs) have attracted much attention due to their excellent luminescent performance. Meanwhile, there is an intent requirement for studying novel red phosphors for WLED with good luminescence properties and without harsh synthesis methods. In this work, a kind of novel double perovskite Sr3WO6:Sm3+, Na+ phosphor was synthesized with a solid-state reaction. The phase purity, morphology, luminescent properties of synthesized phosphors were investigated systematically. At 407 nm excitation, the Sr3WO6:Sm3+, Na+ phosphors exhibited orange-red light (655 nm) attributed to the transition of 4G5/2 → 6H7/2. The optimal doping concentration was 0.02 mol. The quenching temperature (T0.5) of Sr3WO6:0.02Sm3+, 0.02Na+ phosphor was beyond 500 K, which showed the excellent thermal stability of this phosphor. A WLED was fabricated with the phosphor, and related parameters were obtained. The fabricated WLED had a high general color rendering index (Ra = 89) and good correlated color temperature (CCT) (5297 K). Therefore, Sr3WO6:Sm3+, Na+ phosphors were promising candidates for near-ultraviolet (NUV) chip-based WLED and solid-state lighting.
查看更多>>摘要：(Ba0.85Ca0.15)Zr0.1Ti0.9O3 (BCZT) ceramics with donor (Nb5+) and acceptor (Cu2+, Zn2+, Mn2+, Mg2+ ions) doping at B-site were fabricated in this study. The effects of crystal structure, microstructure, and chemical defects, on dielectric properties and piezoelectric coefficient (d33) of all samples, were observed. The addition of Mn2+ and Mg2+ ions could reduce the sintering temperature of BCZT from 1450 °C to 1300 °C; meanwhile, the others did not affect the microstructure of BCZT significantly. The ion substitution influenced the phase fraction, lattice parameters, and tetragonality of BCZT ceramic. The addition of Mg2+ ions decreased greatly Tm of BCZT from ~117 °C to ~76 °C. The addition of Nb5+, Cu2+, and Mn2+ shifted Tm of BCZT to higher temperature. The relationship between decrease of tetragonality and decrease of Tm was observed in these ceramics. The diffuse dielectric behavior of the doped BCZT was induced due to microscopic heterogeneity in the composition. The change in microstructure and the formation of chemical defects (A-site vacancies and oxygen vacancies) significantly affected the polling condition of BCZT ceramic. The crystal structure, microstructure, dielectric, and piezoelectric properties of BCZT ceramic could be modified using these dopants. The results here suggested that BCZT ceramics might become an alternative material for dielectric and piezoelectric devices.
查看更多>>摘要：The recombination of carriers at the photoanode-electrolyte interface is one of the crucial factors hindering the improvement of the photoelectric property of quantum dot-sensitized solar cells (QDSSCs). Passivation layers such as ZnS have been often used to suppress this charge loss, but the effect still needs to be improved. In this paper, Ga3+ is introduced into the traditional ZnS passivation of QDSSCs via a successive ion layer adsorption and reaction (SILAR) approach to further improve the photovoltaic performance. The power conversion efficiency (PCE) of QDSSCs using Zn-Cu-In-Se/Ga-ZnS QDs as sensitizers reaches 8.72%, significantly higher than the 7.7% of Zn-Cu-In-Se/ZnS QDs, demonstrating that the incorporation of Ga3+ in the ZnS layer can optimize the solar absorption and effectively reduce the appearance of carrier recombination, providing a novel means for QDSSCs optimization.
查看更多>>摘要：In the work, the first principles calculation and low temperature spectra were utilized to investigate the modification on Nd3+ clusters in SrF2 crystal. The results show that structures of the clusters vary greatly and it depends on the ionic radius of rare-earth La3+, Nd3+, Gd3+ and Y3+. The cubic sublattice centers are stable in large size rare-earth La3+- and Nd3+-doped SrF2, and the square antiprism centers are more stable in smaller size Gd3+- and Y3+-doped crystals. It suggests that the square antiprism clusters become more stable with decreasing ionic radius in going from La3+, Nd3+, Gd3+ to Y3+, while the cubic sublattice centers become unstable. Based on the results, the mixed [Nd3+-La3+] and [Nd3+-Gd3+] clusters are also calculated. Stability of square antiprism clusters is improved with increasing concentration of Gd3+ in [Nd3+-Gd3+] clusters, and that weakened when codoped with La3+. The results reveal that characteristics of the mixed centers depend on species and contents of the ingredient rare-earth ions. Local environment of the active ions could therefore be modified by codoping the other rare-earth ions, which agreed well with the tunable absorption and emission spectra of Nd3+:SrF2 modified by La3+, Gd3+ and Y3+. The varied cluster structures provide us a methodology towards designing of new rare-earth-doped fluoride materials.
查看更多>>摘要：Al-Ce alloys emerge as promising heat-resist aluminum alloys with service temperatures above 250 °C. Here we report the solidification behavior and the microstructure diversity of Al-Ce alloys, aiming to bridge the gap between solidification condition and microstructures. Both conventional casting and arc surface rapid melting (ASRM) are employed to generate varied solidification conditions. Owing to the large entropy of fusion, intermetallic Al11Ce3 phases are grown in a faceted mode with a strong growth anisotropy, and Chinese-script Al11Ce3/α-Al eutectics are produced upon conventional casting. The addition of Mg restrains the coupled growth of eutectics and promotes the generation of divorced eutectics in cast Al-Ce alloys. Upon rapid solidification during ASRM, regular lamellar and rod-like eutectics prevail in Al-Ce binary alloys, and fishbone eutectics dominate the Al-Ce-Mg ternary alloys. Also, the transition from a hypereutectic microstructure to a fully eutectic microstructure is triggered by ASRM. The interplay of intermetallic Al11Ce3 and Al11Ce3/α-Al eutectics is discussed and the formation of refined regular eutectics is highlighted.
查看更多>>摘要：Highly erbium-doped xEr2O3-44La2O3-(56-x)Al2O3 glasses are synthesized by an aerodynamic levitation (ADL) technique. The optimum erbium-doped concentration in 5Er2O3-44La2O3-51Al2O3 glass can reach ~1.61 × 1021 cm?3. All the fluorescence emission spectra of the glasses under different wavelength bands are measured. The results show the strongest emission intensity at communication band (C-band). The longest radiation lifetime in 4I13/2 → 4I15/2 transition is about ~5.23 ms. The Judd-Ofelt (J-O) parameters of 5Er2O3-44La2O3-51Al2O3 glass are also calculated to evaluate the potential of the glass as a substrate material for optical waveguide amplifier. Based on the parameters of the glass, We used MATLAB to write the gain simulation model of the waveguide amplifier, combined with the COMSOL software to simulate and optimize the waveguide geometry, and calculated the overall gain characteristic curves of optical waveguide amplifiers with different lengths are calculated theoretically. An internal net gain of up to 12.13 dB/cm in the C-band is obtained from the hybrid waveguide amplifier with 1 cm.
查看更多>>摘要：Three pure phases Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 oxyfluorides were successfully prepared using the way of solid-state reaction method at 650 °C, 600 °C and 725 °C, respectively. According to the XRD data and Rietveld refinement results, these three types of ceramics crystallized in a cubic rock salt structure with space group [Fm-3 m(225)]. The grain sizes, theoretical εtheo and packing fraction were calculated to help with the evaluation of these three ceramics. The oxyfluoride ceramics Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 sintered at 875 °C, 900 °C and 900 °C exhibited outstanding microwave dielectric properties: εr = 16.8, 16.4 and 17.3, Q × f = 76,200, 97,300 GHz and 92,600, and τf = ?48.6, ? 40.5 and ? 41.3 ppm/°C, respectively. The compatibility with Ag powders shows that the Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 ceramics are potential candidates for low temperature co-fired ceramic technology.
查看更多>>摘要：M-type barium ferrites (BaM) are utilized in the preparation of ferrite circulators due to their excellent magnetic properties. However, high sintering temperature of BaM is one of the major problems unsuitable for actual production requirements. In this study, Bi3+ ions from the low-melting point oxide bismuth(III) oxide (Bi2O3) were made to substitute Fe3+ ions to reduce the sintering temperature and control the magnetic properties. Addition of an appropriate content of Bi3+ ions at the sintering temperature of 900 °C led to the disappearance of the second phase, and a pure BaBix(CoTi)1.2Fe9.6?xO19 phase was formed. The results exhibited the existence of dense microstructure in BaM ceramics. Moreover, when the x value of Bi2O3 was 0.45, the permeability of the sample increased from 12.59 to 21.6 at 10 MHz, the saturation magnetization reached 3313.34 gauss, and the permittivity increased from 10.75 to 21.24. Permeability and permittivity were found to be approximately equal. Interestingly, addition of excessive Bi2O3 led to the formation of the second phase, and the microstructure exhibited the appearance of abnormal grains. However, BaM still maintained acceptable magnetic properties. The results showed that the addition of Bi3+ ions could reduce the sintering temperature of the ferrite and simultaneously adjust the magnetic and dielectric properties. Therefore, this material may have good performance in the preparation of ferrite circulators.
查看更多>>摘要：Novel Z-scheme 0D/3D p-Ag6Si2O7/n-Bi2O2CO3 micro-flowers heterojunctions were fabricated by a CTAB-aided deposition and in-situ growth route for the first time. The photocatalysts were characterized systematically via XRD, XPS, SEM, BET, EDS, TEM and Mott-Schottky. Under simulated sunlight irradiation, the AB0.15 (the molar ratio of Ag6Si2O7/Bi2O2CO3 is 0.15:1) presented optimal removal rate of methyl orange (0.1064 min?1), which was 18 and 15 times that of Bi2O2CO3 and Ag6Si2O7, respectively. Simultaneously, the AB0.15 can effectively eliminate colourless ciprofloxacin from water (0.0768 min?1), which ruled out the photosensitization. The outstanding organics mineralization ability and photocatalytic stability of AB0.15 were verified by TOC and cyclic tests. As evidenced by UV–vis DRS, PL and electrochemical experiments, AB0.15 exhibited broaden light absorption and improved charge separation efficiency compared with single-phase samples. Trapping experiments and ESR electron spin test proved that h+ and ?O2? were principal active species during the degradation. The performance enhancement was mainly ascribed to the synergistic action of p-n heterojunction built-in electric field and Z-scheme charge migration mode, extremely promoted the activization and separation of carriers. This study offers a new perspective for designing high-performance Z-scheme photocatalysts for sewage purification.
查看更多>>摘要：Electrocaloric effect (ECE) in dielectric materials has attracted much attention due to its promising applications in solid-state cooling devices. In this work, alkaline-earth doped PbZrO3 antiferroelectric thin films (Pb0.9A0.1ZrO3 (A=Ca, Sr, and Ba)) were deposited by a sol-gel method and its antiferroelectric-ferroelectric phase competition as well as the negative ECE were studied. It is found that Ca2+ and Sr2+ expand the antiferroelectric phase region while Ba2+ reduces it, due to the different ion radii of these alkaline-earth elements. As a result, the Pb0.9Sr0.1ZrO3 thin film exhibits an enhanced negative ECE with ΔT of around ? 10.6 K under 450 kV/cm whereas the Pb0.9Ba0.1ZrO3 thin film shows a decreased negative ECE with ΔT of around ? 2.5 K under 200 kV/cm, as compared with the pristine PbZrO3 thin films (with ΔT of around ?7.3 K under 300 kV/cm). This work provides an effective method to enhance the negative ECE of antiferroelectrics in electrical cooling applications by adjusting their antiferroelectric to ferroelectric phase transition.
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