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1.
J Chem Phys ; 151(23): 234703, 2019 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-31864257

RESUMO

Auger nonradiative recombination dominates decay of multicarrier states in high quality colloidal quantum dots (QDs) and thus is critical for many of their optical and optoelectronic applications. Controlling interface-potential smoothness and wavefunction delocalization are proposed as two main strategies for Auger engineering in core/shell QDs. Here, a series of CdSe-based core/shell QDs with nearly ideal optical quality of their single-exciton states are developed and applied for studying biexciton quantum yields and Auger nonradiative recombination rates. Comparative experiments find that the interface-potential smoothness has little influence on biexciton quantum yield and Auger rates of these core/shell QDs with the same CdS outer shells. In contrast, with a fixed total size of the series of QDs, the decreasing hole wavefunction delocalization can increase the Auger rates of positive trions by ∼400%. A mild decrease in electron wavefunction delocalization among the series of QDs results in a small increase in the Auger rates of negative trions (∼50%). Smoothing the core/shell interface can indeed affect the Auger rates, but this is by the way of altering wavefunction delocalization. These findings highlight the importance of control of wavefunction delocalization among the strategies of Auger engineering and provide guidelines for rational design QDs for applications.

2.
Nat Commun ; 10(1): 3078, 2019 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-31289268

RESUMO

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

3.
Nat Commun ; 10(1): 1750, 2019 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-30988287

RESUMO

Auger recombination is the main non-radiative decay pathway for multi-carrier states of colloidal quantum dots, which affects performance of most of their optical and optoelectronic applications. Outstanding single-exciton properties of CdSe/CdS core/shell quantum dots enable us to simultaneously study the two basic types of Auger recombination channels-negative trion and positive trion channels. Though Auger rates of positive trion are regarded to be much faster than that of negative trion for II-VI quantum dots in literature, our experiments find the two rates can be inverted for certain core/shell geometries. This is confirmed by theoretical calculations as a result of geometry-dependent dielectric screening. By varying the core/shell geometry, both types of Auger rates can be independently tuned for ~ 1 order of magnitude. Experimental and theoretical findings shed new light on designing quantum dots with necessary Auger recombination characteristics for high-power light-emitting-diodes, lasers, single-molecular tracking, super-resolution microscope, and advanced quantum light sources.

4.
Zhongguo Zhong Yao Za Zhi ; 44(2): 265-269, 2019 Jan.
Artigo em Chinês | MEDLINE | ID: mdl-30989943

RESUMO

This study is based on the data analysis of medicinal plant resources and diversity collected from the fourth Chinese traditional medicine resource survey( pilot). Through the analysis of relevant data from 33 census pioneer plots in Guizhou province( area),a total of 265 families,1 432 genera and 5 296 species of medicinal resources were reported,including algae,fungi,lichens,mosses,a total of 43 genera and 35 families,57,48 families,120 genera and 453 species of ferns,gymnosperms 11 families,22 genera and 61 species,167 families,1 243 genera and 4 721 species of angiosperms,4 genera and 4 families four medicinal animals.Compared with the data related to the third survey of traditional Chinese medicine resources,the number of ferns,gymnosperms and angiosperms in the fourth survey has increased far more than that of the third survey. From the regional distribution of medicinal resources,the composition of the genus,the type of life,and the location of the medicine,the richness of the medicinal plant resources in Guizhou province is not only reflected in many types,but also in the variety of medicinal resources. These studies provide a scientific basis for vigorously developing the Chinese herbal medicine industry and the sustainably using medicinal plant resources in Guizhou province.


Assuntos
Medicamentos de Ervas Chinesas , Medicina Tradicional Chinesa , Plantas Medicinais/classificação , China , Cycadopsida , Gleiquênias , Magnoliopsida
5.
J Am Chem Soc ; 141(16): 6448-6452, 2019 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-30964282

RESUMO

We introduce stoichiometry control within both core and shell regions of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) to advance their properties drastically, approaching those of state-of-the-art CdSe-based QDs. The resulting QDs possess near-unity photoluminescence quantum yield, monoexponential decay dynamics, narrow line width, and nonblinking at a single-dot level. Quantum-dot light-emitting diodes (QLEDs) with the InP/ZnSe/ZnS core/shell/shell QDs as emitters exhibit a peak external quantum efficiency of 12.2% and a maximum brightness of >10 000 cd m-2, greatly exceeding those of the Cd/Pb-free QLEDs reported in literature. These results pave the way toward Cd/Pb-free QDs as outstanding optical and optoelectronic materials.

6.
Sci Rep ; 8(1): 9424, 2018 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-29930263

RESUMO

Medicinal herbs of high quality and with significant clinical effects have been designated as top-geoherbs in traditional Chinese medicine (TCM). However, the validity of this concept using genetic markers has not been widely tested. In this study, we investigated the genetic variation within the Rheum palmatum complex (rhubarb), an important herbal remedy in TCM, using a phylogeographic (six chloroplast DNA regions, five nuclear DNA regions, and 14 nuclear microsatellite loci) and a chemical approach (anthraquinone content). Genetic and chemical data identified two distinct groups in the 38 analysed populations from the R. palmatum complex which geographically coincide with the traditional top-geoherb and non-top-geoherb areas of rhubarb. Molecular dating suggests that the two groups diverged in the Quaternary c. 2.0 million years ago, a time of repeated climate changes and uplift of the Qinghai-Tibetan Plateau. Our results show that the ancient TCM concept of top-geoherb and non-top-geoherb areas corresponds to genetically and chemically differentiated groups in rhubarb.


Assuntos
Polimorfismo Genético , Rheum/genética , Ecossistema , Genoma de Cloroplastos , Repetições de Microssatélites , Plantas Medicinais/química , Plantas Medicinais/genética , Rheum/química
7.
Nano Lett ; 17(12): 7487-7493, 2017 12 13.
Artigo em Inglês | MEDLINE | ID: mdl-29160715

RESUMO

Upon photo- or electrical-excitation, colloidal quantum dots (QDs) are often found in multicarrier states due to multiphoton absorption, photocharging, or imbalanced carrier injection of the QDs. While many of these multicarrier states are observed in single-dot spectroscopy, their properties are not well studied due to random charging/discharging, emission intensity intermittency, and uncontrolled surface defects of single QDs. Here we report in situ deciphering of the charging status, precisely assessing the absorption cross section, and determining the absolute emission quantum yield of monoexciton and biexciton states for neutral, positively charged, and negatively charged single core/shell CdSe/CdS QDs. We uncover very different photon statistics of the three charge states in single QDs and unambiguously identify their charge signs together with the information on their photoluminescence decay dynamics. We then show their distinct photoluminescence saturation behaviors and evaluate the absolute values of absorption cross sections and quantum efficiencies of monoexcitons and biexcitons. We demonstrate that the addition of an extra hole or electron in a QD not only changes its emission properties but also varies its absorption cross section.

8.
J Am Chem Soc ; 138(20): 6475-83, 2016 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-27144923

RESUMO

CdSe magic-size clusters with close-shell surface and fixed molecular formula are well-known in the size range between ∼1 and 3 nm. By applying high concentration of cadmium alkanoates as ligands, a conventional synthetic system for CdSe nanocrystals was tuned to discriminate completion from initiation of atomic flat facets. This resulted in ∼4-13 nm CdSe nanocrystals with hexahedral shape terminated with low-index facets, namely three (100), one (110), and two (111) facets. These low-symmetry (Cs group with single mirror plane) yet monodisperse hexahedra were found to be persistent not only in a broad size range but also under typical synthetic temperatures for growth of both CdSe and CdS. Atomic motion on the surface of the nanocrystals under enhanced ligand dynamics initiated intraparticle ripening without activating interparticle ripening, which converted the hexahedral nanocrystals to monodisperse spherical ones. This new synthetic strategy rendered optimal color purity of photoluminescence (PL) of the CdSe and CdSe/CdS core/shell nanocrystals, with the ensemble PL peak width comparable with that of a corresponding single dot.

9.
PLoS One ; 9(10): e110760, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25349989

RESUMO

AIMS: Rheum palmatum complex comprises all taxa within section Palmata in the genus Rheum, including R. officinale, R. palmatum, R. tanguticum, R. tanguticum var. liupanshanense and R. laciniatum. The identification of the taxa in section Palmata is based primarily on the degree of leaf blade dissection and the shape of the lobes; however, difficulties in species identification may arise from their significant variation. The aim of this study is to analyze the patterns of variation in leaf blade characteristics within and among populations through population-based sampling covering the entire distribution range of R. palmatum complex. METHODS: Samples were taken from 2340 leaves from 780 individuals and 44 populations representing the four species, and the degree of leaf blade dissection and the shape of the lobe were measured to yield a set of quantitative data. Furthermore, those data were statistically analyzed. IMPORTANT FINDINGS: The statistical analysis showed that the degree of leaf blade dissection is continuous from lobed to parted, and the shape of the lobe is also continuous from broadly triangular to lanceolate both within and between populations. We suggested that taxa in section Palmata should be considered as one species. Based on the research on the R. palmatum complex, we considered that the quantitative characteristics were greatly influenced by the environment. Therefore, it is not reliable to delimitate the species according to the continuously quantitative vegetative characteristics.


Assuntos
Folhas de Planta/anatomia & histologia , Rheum/anatomia & histologia , Meio Ambiente , Geografia , Fenótipo
10.
Int J Mol Sci ; 13(3): 3900-15, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22489188

RESUMO

Rheum officinale Baill., an important but endangered medicinal herb, is endemic to China. Inter-simple sequence repeat (ISSR) markers were employed to investigate the genetic diversity and differentiation of 12 populations of R. officinale. Thirteen selected primers yielded 189 bright and discernible bands, with an average of 14.54 per primer. The genetic diversity was low at the population level, but pretty high at the species level (H = 0.1008, I = 0.1505, PPB = 28.95% vs. H = 0.3341, I = 0.5000, PPB = 95.24%, respectively) by POPGENE analysis. Analysis of molecular variance (AMOVA) showed that the genetic variation was found mainly among populations (74.38%), in line with the limited gene flow (N(m) = 0.2766) among populations. Mantel test revealed a significant correlation between genetic and geographic distances (r = 0.5381, P = 0.002), indicating the role of geographic isolation in shaping the present population genetic structure. Both Bayesian analysis and UPGMA cluster analysis demonstrated the similar results. Our results imply that the conservation efforts should aim to preserve all the extant populations of this endangered species, and cultivation is proposed in this study.


Assuntos
Repetições de Microssatélites/genética , Isolamento Reprodutivo , Rheum/genética , Sequência de Bases , Análise por Conglomerados , Primers do DNA/genética , Fluxo Gênico , Variação Genética , Genética Populacional , Geografia , Plantas Medicinais/genética , Rheum/classificação , Análise de Sequência de DNA
11.
PLoS One ; 7(12): e51667, 2012 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-23289054

RESUMO

AIMS: Both Rheum palmatum and R. tanguticum are important but endangered medicinal plants endemic to China. In this study, we aimed to (i) investigate the level and pattern of genetic variability within/among populations of those species; (ii) evaluate genetic differentiation between both species and its relationships and ascertain whether both species are consistent with their current taxonomical treatment as separate species; and (iii) discuss the implications for the effective conservation of two species. METHODS: Total 574 individuals from 30 populations of R. palmatum and R. tanguticum were collected, covering the entire distribution range of two species in China. The genetic variation within and among 30 populations was evaluated using inter-simple sequence repeat (ISSR) markers. IMPORTANT FINDINGS: Twelve selected ISSR primers generated a total of 175 fragments, 173 (98.86%) of which were polymorphic. The Nei's gene diversity (H) and Shannon's index (I) of both species were high at species level (H = 0.3107, I = 0.4677 for R. palmatum; H = 0.2848, I = 0.4333 for R. tanguticum). But for both species, the genetic diversity was low at population level, and average within-population diversity of R. palmatum was H = 0.1438, I = 0.2151, and that of R. tanguticum was H = 0.1415, I = 0.2126. The hierarchical AMOVA revealed high levels of among-population genetic differentiation in both species, in line with the gene differentiation coefficient and the limited among-population gene flow (R. palmatum: Φ(st) = 0.592, G(st) = 0.537, N(m) = 0.432; R. tanguticum: Φ(st) = 0.567, G(st) = 0.497, N(m) = 0.507). By contrast, only 6.52% of the total genetic variance was partitioned between R. palmatum and R. tanguticum. Bayesian analysis, UPGMA cluster analysis, and PCoA analysis all demonstrated the similar results. A significant isolation-by-distance pattern was revealed in R. palmatum (r = 0.547, P = 0.010), but not in R. tanguticum (r = 0.241, P = 0.100). Based on these results, effective conservation strategies were proposed for these two species. The small molecular variance between R. palmatum and R. tanguticum revealed that they had a common ancestor, and we considered that these two species might not be good species.


Assuntos
Genética Populacional , Repetições de Microssatélites/genética , Rheum/genética , Teorema de Bayes , China , Espécies em Perigo de Extinção , Variação Genética , Humanos , Medicina Tradicional Chinesa , Filogenia , Rheum/química
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