Ce^(3+):Lu_(3)Al_(5)O_(12)–Al_(2)O_(3) optical nanoceramic scintillators elaborated via a low-temperature glass crystallization route

Transparent Ce:lutetium aluminum garnet(Ce:Lu_(3)A_(l5)O_(12),Ce:LuAG)ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number(Zeff).However,the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of LuAl antisite defects at high sintering temperatures.This work demonstrates a low-temperature(1100℃)synthetic strategy for elaborating transparent LuAG–Al_(2)O_(3) nanoceramics through the crystallization of 72 mol%Al_(2)O_(3)–28 mol%Lu_(2)O_(3)(ALu28)bulk glass.The biphasic nanostructure composed of LuAG and Al_(2)O_(3) nanocrystals makes up the whole ceramic materials.Most of Al_(2)O_(3) is distributed among LuAG grains,and the rest is present inside the LuAG grains.Fully dense biphasic LuAG–Al_(2)O_(3) nanoceramics are highly transparent from the visible region to mid-infrared(MIR)region,and particularly the transmittance reaches 82%at 780 nm.Moreover,LuAl antisite defect-related centers are completely undetectable in X-ray excited luminescence(XEL)spectra of Ce:LuAG–Al_(2)O_(3) nanoceramics with 0.3–1.0 at%Ce.The light yield of 0.3 at%Ce:LuAG–Al_(2)O_(3) nanoceramics is estimated to be 20,000 ph/MeV with short 1μs shaping time,which is far superior to that of commercial Bi_(4)Ge_(3)O_(12)(BGO)single crystals.These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics,and is promising to produce garnet-based ceramic materials with excellent properties,thereby meeting the demands of advanced scintillation applications.

Biphasic (Lu,Gd)_(3)Al_(5)O_(12)-based transparent nanoceramic color converters for high-power white LED/LD lighting

Ce doped Lu_(3)Al_(5)O_(12)(Ce:LuAG)transparent ceramics are considered as promising color converters for solid-state lighting because of their excellent luminous efficiency,high thermal quenching temperature,and good thermal stability.However,Ce:LuAG ceramics mainly emit green light.The shortage of red light as well as the expensive price of Lu compounds are hindering their application for white lighting.In this work,transparent(Lu,Gd)_(3)Al_(5)O_(12)–Al_(2)O_(3)(LuGAG–Al_(2)O_(3))nanoceramics with different replacing contents of Gd^(3+)(10%–50%)were successfully elaborated via a glass-crystallization method.The obtained ceramics with full nanoscale grains are composed of the main LuGAG crystalline phase and secondary Al_(2)O_(3) phase,exhibiting eminent transparency of 81.0%@780 nm.After doping by Ce^(3+),the Ce:LuGAG–Al_(2)O_(3) nanoceramics show a significant red shift(510 nm→550 nm)and make up for the deficiency of red light component in the emission spectrum.The Ce:LuAG–Al_(2)O_(3) nanoceramics with 20%Gd^(3+)show high internal quantum efficiency(81.5%in internal quantum efficiency(IQE),96.7%of Ce:LuAG–Al_(2)O_(3) nanoceramics)and good thermal stability(only 9%loss in IQE at 150℃).When combined with blue LED chips(10 W),0.3%Ce:LuGAG–Al_(2)O_(3) nanoceramics with 20%Gd^(3+)successfully realize the high-quality warm white LED lighting with a color coordinate of(0.3566,0.435),a color temperature of 4347 K,CRI of 67.7,and a luminous efficiency of 175.8 lm·W^(−1).When the transparent 0.3%Ce:LuGAG–Al_(2)O_(3) nanoceramics are excited by blue laser(5 W·mm^(−2)),the emission peak position redshifts from 517 to 570 nm,the emitted light exhibits a continuous change from green light to yellow light,and then to orange-yellow light,and the maximum luminous efficiency is up to 234.49 lm·W^(−1)(20%Gd^(3+)).Taking into account the high quantum efficiency,good thermal stability,and excellent and adjustable luminous properties,the transparent Ce:LuGAG–Al_(2)O_(3) nanoceramics with different Gd^(3+)substitution contents in this paper are believed to be promising candidates for high-power white LED/LD lighting.

Gas sensing capabilities of TiO_(2) porous nanoceramics prepared through premature sintering

Pure and noble metal(Pt,Pd,and Au)doped TiO_(2)nanoceramics have been prepared from TiO_(2)nanoparticles through traditional pressing and sintering.For those samples sintered at 550℃,a typical premature sintering occurred,which led to the formation of a highly porous microstructure with a Brunauer-Emmett-Teller(BET)specific surface area of 23 m^(2)/g.At room temperature,only Pt-doped samples showed obvious response to hydrogen,with sensitivities as high as~500 for 1000 ppm H_(2)in N_(2);at 300℃,all samples showed obvious responses to CO,while the responses of noble metal doped samples were much higher than that of the undoped ones.The mechanism for the observed sensing capabilities has been discussed,in which the catalytic effect of Pt for hydrogen is believed responsible for the room-temperature hydrogen sensing capabilities,and the absence of glass frit as commonly used in commercial thick-film metal oxide gas sensors is related to the high sensitivities.It is proposed that much attention should be paid to metal oxide porous nanoceramics in developing gas sensors with high sensitivities and low working temperatures.

New progress in development of ferroelectric and piezoelectric nanoceramics

There has been great progress in the last decade in the synthesis of nanopowders with highly controlled size and size distribution.Meanwhile,the development of an unconventional pressureless two-step sintering strategy enabling densification without grain growth provides a novel technology suitable for commercial production of nanograin ceramics.The particular interest concerning bulk dense nanograin ceramics is the manifestation of ferroelectricity,which remains a fundamental issue to be understood and exploited.Combining the best powder synthesis and optimized two-step sintering,high-density barium titanate(BT)and related nanograin ceramics have been fabricated to allow for a detailed determination of the size effect on nanometer-scale ferroelectricity and piezoelectricity of fundamental and industrial interest.These include dense ceramics of undoped BT with an average grain size down to 5 nm,and of(1x)BiScO_(3)xPbTiO_(3)(BSPT)solid solutions with an average grain size down to 10 nm.Here we review the fabrication methods of high-density BT and BSPT nanoceramics and the major findings of the size effect on their microstructure,phase transition and electrical properties.Robust ferroelectricity is demonstrated for the first time in 5 nm BT nanoceramics,while strong local piezoelectricity is present in 10 nm BSPT nanoceramics.

Magnetic studies of GaN nanoceramics doped with 1% of cerium

The magnetization measurements of gallium nitride nanoceramics doped with 1% of cerium and sintered under various pressures were reported. It was found that GaN nanoceramics doped with cerium showed paramagnetic behavior in the wide temperature range. Nanoceramics of GaN with 1% of Ce （as undoped GaN） was diamagnetic one, but under certain temperature the paramagnetic properties started to dominate. This crossover temperature was nonlinearly dependent on the pressure applied during the sintering. The fitting of molar magnetic susceptibility allowed to estimate the Curie temperature, Curie constant and diamagnetic part of susceptibility. As it was found, all the samples showed the antiferromagnetic ordering with θp≈-1 K. Also, the effective magnetic moment was estimated for all of the samples. As a result, magnetic moments in terms of Ce ion were notably larger in comparison with those obtained within the Russell-Saunders cou- pling model. We suggested that it was the strong influence of amorphous shell which was rising with the pressure applied during the sintering. Finally, we presented dependences of magnetization as a function of applied field. All the samples manifested weak ferromagnetism at high temperatures and paramagnetic behavior in low temperature region.

The modulation of stem cell behaviors by functionalized nanoceramic coatings on Ti-based implants

Nanoceramic coating on the surface of Ti-based metallic implants is a clinical potential option in orthopedic surgery.Stem cells have been found to have osteogenic capabilities.It is necessary to study the influences of functionalized nanoceramic coatings on the differentiation and proliferation of stem cells in vitro or in vivo.In this paper,we summarized the recent advance on the modulation of stem cells behaviors through controlling the properties of nanoceramic coatings,including surface chemistry,surface roughness and microporosity.In addition,mechanotransduction pathways have also been discussed to reveal the interaction mechanisms between the stem cells and ceramic coatings on Ti-based metals.In the final part,the osteoinduction and osteoconduction of ceramic coating have been also presented when it was used as carrier of BMPs in new bone formation.

Contrasting room-temperature hydrogen sensing capabilities of Pt-SnO2 and Pt-TiO2 composite nanoceramics

Contrasting room-temperature hydrogen sensing behaviors have been revealed for Pt-TiO2 and Pt-SnO2 composite nanoceramics. In the case of the Pt-TiO2 nanoceramics, the ultrahigh hydrogen sensitivities are lost abruptly when the oxygen/hydrogen concentration ratio in ambient atmosphere reaches a critical value. However, in the case of the Pt-SnO2 nanoceramics, such a phenomenon does not occur, and the extraordinary room-temperature hydrogen sensing capabilities are observed in the presence of oxygen in air. Our combined experimental and theoretical investigations establish a unified mechanism for both the systems, which is rooted in hydrogen chemisorption on the surface and interstitial lattice sites of SnO2 and TiO2; the difference in stability of the chemisorbed hydrogen on SnO2 and TiO2 is considered responsible for the contrasting hydrogen sensing capabilities. The central findings are helpful in enriching our microscopic understanding of hydrogen interaction with various metal oxide semiconductors （MOSs） at room temperature in varying mixed gaseous concentrations, and they could be instrumental in developing reliable room-temperature hydrogen sensors based on bulk MOSs.

Dielectric and ferroelectric properties of CoCr_(2)O_(4)nanoceramics

CoCr_(2)O_(4)nanoceramics are prepared by sol-gel auto combustion method.Synchrotron X-ray diffraction analysis affirms the singlephasepristine cubic structure with space group Fd3m.Debye-Scherrer method estimates the crystallite size of main intense peak tobe~27:15 nm.Prominent bands obtained in infrared spectra at 448 and 599 cm^(-1)are due to metal-oxygen stretching bond presentat tetrahedral and octahedral sites.Dielectric parameters decrease as frequency increases from 103 to 106 Hz that can be interpretedby Maxwell-Wagner-type interfacial polarization.Complex impedance spectra(Nyquist plot)reveal arc like behavior,which ismainly due to intergrain(grain boundary)resistance that also exhibits conducting nature of the nanoceramics.Weak ferroelectricityis mainly associated with the partial reversal of the polarization.Leakage current behavior follows the Ohmic and Child square law.Electron conduction process was interpreted by space-charge limited current(SCLC)mechanism.Leakage current behaviorobserved in cobalt chromite nanoceramics is mainly attributed to the oxygen vacancies.

Nanostructured Ceramics of Potassium Sodium Bismuth Titanate: Hydrothermal Synthesis and Piezoelectric Response at Morphotropic Phase Boundary

Potassium Sodium Bismuth Titanate (KNBT) ceramics, with the general formula (1 - x)K0.5Bi0.5TiO3 -xNa0.5Bi0.5TiO3, have been synthesized following hydrothermal route, starting with solid solutions of pure perovskite nanoceramics of KBT and NBT in desired stoichiometric weight ratios, followed by sintering between 850°C and 1000°C for few hours. Pure KNBT nanoceramics with perovskite structure, having mean particle size around 30 nm, could be obtained. Morphology of the samples is found to depend strongly on composition. A change of composition results in a phase change, as evident from X-ray structure analysis. This phase change is a result of rhombohedral to tetragonal morphotropic phase boundary (MPB) in the sample with x around 0.80. Composition dependent occurrence of MPB leads to formation of needle like structures with micrometer length scales. These are typical of tetragonal lamellar structures, suggesting partial induction of tetragonal polar order from rhombohedral structure at MPB. Dielectric and piezoelectric properties, such as dielectric constant and loss, piezoelectric coefficients and figures of merit, exhibit threshold maxima in their values at the composition corresponding to MPB. These values reported for a lead-free piezoceramic, synthesized by a comparatively simple hydrothermal route, are highly promising, and comparable to well-known PZT.

环境水体中GⅡ型诺如病毒浓缩研究

自行设计一种适合野外现场采样的病毒采集浓缩仪,采用一种新型阳离子膜NanoCeram,进行环境水体中GⅡ型诺如病毒浓缩研究。通过预实验,考察了预处理膜、不同的二次浓缩方法、不同洗脱液对病毒回收率的影响,随后优化整个浓缩过程并确定最佳的病毒浓缩方法。结果显示,预处理膜对病毒回收影响较大,PEG-NaCl沉淀、硅藻土吸附这两种二次浓缩方法的效果相当,选择0.15mol/L Na2HPO4作为硅藻土洗脱液。确定了NanoCeram阳离子膜的病毒回收率为3.02%。最后对北京市丰台区洋桥生活污水进行现场采样,成功检测到GⅡ型诺如病毒,证明该方法有效可行,适合于环境水体中诺如病毒的浓缩分离和检测。

水体中诺如病毒富集技术的研究

目的评估不同实验条件下NanoCeram-PEG富集法对水中诺如病毒(NV)的富集效果,以获得较优的富集方法。方法构建诺如病毒阳性标准质粒,以此为模板,应用荧光定量RT-PCR方法绘制病毒定量标准曲线;将含诺如病毒粪便悬液加入纯净水中,在不同实验条件下经富集操作,富集液经荧光定量RT-PCR方法进行绝对定量并计算最终回收率,从而确定最优富集方法。结果通过病毒定量标准曲线确定荧光定量RT-PCR方法对水中诺如病毒的检测灵敏度为100 copy/μl。本实验通过正交设计方法考察了洗脱液p H值、洗脱速度和PEG浓度3个因素对最终病毒回收率的影响,最终确定在洗脱液流速为300 ml/min,洗脱液p H值为9.5,PEG6000浓度为13%的条件下病毒回收率最高,达到26.55%。结论证明NanoCeram-PEG富集法具有较好的病毒回收率,加以发展将为水源性诺如病毒疫情的溯源提供可靠的实验室依据。