Multicolor luminescent rare-earth ion-doped Y2O3 nanocrystals （NCs） were prepared by a solvethermal method. The as-synthesized NCs yielded nanosheets, nanowires （NWs） and nanorods （NRs） with the increase of alka...Multicolor luminescent rare-earth ion-doped Y2O3 nanocrystals （NCs） were prepared by a solvethermal method. The as-synthesized NCs yielded nanosheets, nanowires （NWs） and nanorods （NRs） with the increase of alkali （NaOH） in oleic acid system. Moreover, Y203 nanowires with controllable size have also been obtained. After sintering, the PL intensity of Y2O3：Ln3＋ nanocrystals increased with the changed morphology of the precursor, that is, Y（OH）3 nanocrystals. Both downconversion （red emission for Y2O3：Eu3＋ and green emission for Y2O3：Tb3＋） and upconversion （red emission for Y2O3：Yb/Er3＋） luminescence of the as-prepared nanocrystals have been demonstrated in this work. We also found that the PL intensity of Y2O3：Ln3＋ NCs dispersed in polar solvent was stronger than that in nonpolar solvent. Their up/downconversion fluorescence and controllable morphology might promise further fundamental research and biochemistry such as nanoscale optoelectronics, nanolasers, and ultrasensitive multicolor biolables.展开更多
Structural and thermal sensitivity of Cu(60-x)Zr(30+x) Ti 10 (x=0,5,and 10 at%) amorphous alloys to the application of tension was investigated. The structural sensitivity to tension decreases with increasing Cu conte...Structural and thermal sensitivity of Cu(60-x)Zr(30+x) Ti 10 (x=0,5,and 10 at%) amorphous alloys to the application of tension was investigated. The structural sensitivity to tension decreases with increasing Cu content. The crystallization enthalpy increases with increasing excess free volume. The characteristic temperatures of the tensile samples can surpass those of the as-cast ones under a critical heating rate which differs in the Cu content. The increase of the excess free volume significantly influences the glass transition and crystallization procedures.展开更多
Atomically thin solid-state channels enabling selective molecular transport could potentially be used in a variety of separation and energy conversion applications.The density of channels,their height,distance and edg...Atomically thin solid-state channels enabling selective molecular transport could potentially be used in a variety of separation and energy conversion applications.The density of channels,their height,distance and edge structure are the key factors that dramatically impact the selective transport performance.However,such channels with small constrictions and atomic precision have been limited to proof-ofconcept demonstrations based on microscale two-dimensional(2D)crystal stripes.Here,we report the engineering of highly ordered,scalable monolayer graphene crystallite arrays by chemical vapor deposition(CVD)method with a modified anisotropic etching approach.The size,shape,distance and edge structure of the graphene crystallite arrays in a large area could be delicately controlled through tailoring the synthetic parameters.This array structure can act as pillars to prop up a smooth single-crystal graphene film,and the fabricated integrated angstrom-size(3.4A)channels allow water transport but exclude hydrated ions,demonstrating potential in selective ionic sieving and nanofiltration practice.展开更多
Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpenty...Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpentyloxy]phenyl}styrene （Ic）, （＋）-2,5-bis{4＇-[（S）-4＂- methylhexyloxy]phenyl}styrene （Id）, （-）-2,5-bis{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （le）, （＋）-2-/4＇-[（S）-l＂-methyl- propyloxy]phenyl}-5-{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （Ⅱa）, （-）-2-{4＇-[（R）-1＂-methylpropyloxy]phenyl}-5-{4＇- [（S）- 1 ＂-methylpropyloxy]phenyl } styrene （lib）, and （＋）-2- { 4＇-[（S）-2＂-methylbutyloxy]phenyl }-5- { 4＇-[（S）- 1＂-methylpropyl- oxy]phenyl}styrene （Ⅲ）, were synthesized and radically polymerized. These molecules were designed to further understand long-range chirality transfer in radical polymerization and to possibly tune the chiroptical properties of the polymers by varying the spatial configuration, position, and various combination of the stereogenic centers at the ends ofp-terphenyl pendants. The resultant polymers adopted helical conformations with a predominant screw sense. When the stereogenic centers ran away from the terphenyl group as in Ⅰb-d, the corresponding polymers changed the direction of optical rotation in an alternative way and showed no obvious stereomutation upon annealing in tetrahydrofuran. The two stereogenic centers of Ⅱa, Ⅱb, and Ⅲ acted concertedly in chiral induction, whereas those of la and Ie played a counteractive role. The five polymers derived from Ⅰa, Ⅰe, Ⅱa, Ⅱb, and Ⅲ underwent stereomutation when annealed in tetrahydrofuran. The polymers PIa-e had good thermal stability and high glass transition temperatures （Tgs）. They generated liquid crystalline phases at above Tgs that could be kept upon cooling, with the exception of Pie. This result was consistent with the extended helical structures.展开更多
文摘Multicolor luminescent rare-earth ion-doped Y2O3 nanocrystals （NCs） were prepared by a solvethermal method. The as-synthesized NCs yielded nanosheets, nanowires （NWs） and nanorods （NRs） with the increase of alkali （NaOH） in oleic acid system. Moreover, Y203 nanowires with controllable size have also been obtained. After sintering, the PL intensity of Y2O3：Ln3＋ nanocrystals increased with the changed morphology of the precursor, that is, Y（OH）3 nanocrystals. Both downconversion （red emission for Y2O3：Eu3＋ and green emission for Y2O3：Tb3＋） and upconversion （red emission for Y2O3：Yb/Er3＋） luminescence of the as-prepared nanocrystals have been demonstrated in this work. We also found that the PL intensity of Y2O3：Ln3＋ NCs dispersed in polar solvent was stronger than that in nonpolar solvent. Their up/downconversion fluorescence and controllable morphology might promise further fundamental research and biochemistry such as nanoscale optoelectronics, nanolasers, and ultrasensitive multicolor biolables.
基金the National Natural Science Foundation (Grant No. 50874045)the Scientific Research Fund of the Hunan Provincial Education Department (Grant No. 10A044)
文摘Structural and thermal sensitivity of Cu(60-x)Zr(30+x) Ti 10 (x=0,5,and 10 at%) amorphous alloys to the application of tension was investigated. The structural sensitivity to tension decreases with increasing Cu content. The crystallization enthalpy increases with increasing excess free volume. The characteristic temperatures of the tensile samples can surpass those of the as-cast ones under a critical heating rate which differs in the Cu content. The increase of the excess free volume significantly influences the glass transition and crystallization procedures.
基金the National Natural Science Foundation of China(51772110,61890940)。
文摘Atomically thin solid-state channels enabling selective molecular transport could potentially be used in a variety of separation and energy conversion applications.The density of channels,their height,distance and edge structure are the key factors that dramatically impact the selective transport performance.However,such channels with small constrictions and atomic precision have been limited to proof-ofconcept demonstrations based on microscale two-dimensional(2D)crystal stripes.Here,we report the engineering of highly ordered,scalable monolayer graphene crystallite arrays by chemical vapor deposition(CVD)method with a modified anisotropic etching approach.The size,shape,distance and edge structure of the graphene crystallite arrays in a large area could be delicately controlled through tailoring the synthetic parameters.This array structure can act as pillars to prop up a smooth single-crystal graphene film,and the fabricated integrated angstrom-size(3.4A)channels allow water transport but exclude hydrated ions,demonstrating potential in selective ionic sieving and nanofiltration practice.
基金supported by the National Natural Science Foundation of China(21274003)the Research Fund for Doctoral Program of Higher Education of Ministry of Education(20110001110084)
文摘Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpentyloxy]phenyl}styrene （Ic）, （＋）-2,5-bis{4＇-[（S）-4＂- methylhexyloxy]phenyl}styrene （Id）, （-）-2,5-bis{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （le）, （＋）-2-/4＇-[（S）-l＂-methyl- propyloxy]phenyl}-5-{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （Ⅱa）, （-）-2-{4＇-[（R）-1＂-methylpropyloxy]phenyl}-5-{4＇- [（S）- 1 ＂-methylpropyloxy]phenyl } styrene （lib）, and （＋）-2- { 4＇-[（S）-2＂-methylbutyloxy]phenyl }-5- { 4＇-[（S）- 1＂-methylpropyl- oxy]phenyl}styrene （Ⅲ）, were synthesized and radically polymerized. These molecules were designed to further understand long-range chirality transfer in radical polymerization and to possibly tune the chiroptical properties of the polymers by varying the spatial configuration, position, and various combination of the stereogenic centers at the ends ofp-terphenyl pendants. The resultant polymers adopted helical conformations with a predominant screw sense. When the stereogenic centers ran away from the terphenyl group as in Ⅰb-d, the corresponding polymers changed the direction of optical rotation in an alternative way and showed no obvious stereomutation upon annealing in tetrahydrofuran. The two stereogenic centers of Ⅱa, Ⅱb, and Ⅲ acted concertedly in chiral induction, whereas those of la and Ie played a counteractive role. The five polymers derived from Ⅰa, Ⅰe, Ⅱa, Ⅱb, and Ⅲ underwent stereomutation when annealed in tetrahydrofuran. The polymers PIa-e had good thermal stability and high glass transition temperatures （Tgs）. They generated liquid crystalline phases at above Tgs that could be kept upon cooling, with the exception of Pie. This result was consistent with the extended helical structures.
