This review article provides an overview of recent advances in the study and understanding of dynamics of excitons in semiconductor nanocrystals (NCs) or quantum dots (QDs). Emphasis is placed on the ...relationship between exciton dynamics and optical properties, both linear and nonlinear. We also focus on the unique aspects of exciton dynamics in semiconductor NCs as compared to those in bulk crystals. Various experimental techniques for probing exciton dynamics, particularly time‐resolved laser methods, are reviewed. Relevant models and computational studies are also briefly presented. By comparing different materials systems, a unifying picture is proposed to account for the major dynamic features of excitons in semiconductor QDs. While the specific dynamic processes involved are material‐dependent, key processes can be identified for all the materials that include electronic dephasing, intraband relaxation, trapping, and interband recombination of free and trapped charge carriers (electron and hole). Exciton dynamics play a critical role in the fundamental properties and functionalities of nanomaterials of interest for a variety of applications including optical detectors, solar energy conversion, lasers, and sensors. A better understanding of exciton dynamics in nanomaterials is thus important both fundamentally and technologically.
Semiconductor nanocrystals possess exceptional optical and electronic properties useful for technologies including optical detectors, solar energy conversion, and sensors. In particular, exciton dynamics play a critical role in the properties of these nanocrystals. In this review, the unique aspects of the exciton are presented, including electronic dephasing, intraband relaxation, trapping, and interband recombination charge carriers along with relevant models and computational studies.
A new strategy has been developed using peptides with amino and carboxylic functional groups as passivating ligands to produce methyl ammonium lead bromide (CH3NH3PbBr3) perovskite nanocrystals ...(PNCs) with excellent optical properties. The well‐passivated PNCs can only be obtained when both amino and carboxylic groups are involved, and this is attributed to the protonation reaction between NH2 and COOH that is essential for successful passivation of the PNCs. To better understand this synergistic effect, peptides with different lengths have been studied and compared. Due to the polar nature of peptides, peptide‐passivated PNCs (denoted as PNCspeptide) aggregate and precipitate from nonpolar toluene solvent, resulting in a high product yield (≈44%). Furthermore, the size of PNCspeptide can be varied from ≈3.9 to 8.6 nm by adjusting the concentration of the peptide, resulting in tunable optical properties due to the quantum confinement effect. In addition, CsPbBr3 PNCs are also synthesized with peptides as capping ligands, further demonstrating the generality and versatility of this strategy, which is important for generating high quality PNCs for photonics applications including light‐emitting diodes, optical sensing, and imaging.
Peptides with different lengths are used in the synthesis of perovskite nanocrystals (PNCs) as capping ligands. PNCspeptide with tunable size (≈3.9 to 8.6 nm), prepared by adjusting the concentration of the peptides, exhibit size‐dependent optical properties due to quantum confinement effect. Such PNCs with peptides conjugated on their surface have potential applications in biomedicine, including optical sensing and imaging.
We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite ...nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn4+ substitution at Fe3+ sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm2 at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm2 at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron−hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.
Optical properties are among the most fascinating and useful properties of nanomaterials and have been extensively studied using a variety of optical spectroscopic techniques. A basic understanding ...of the optical properties and related spectroscopic techniques is essential for anyone who is interested in learning about nanomaterials of semiconductors, insulators or metal. This is partly because optical properties are intimately related to other properties and functionalities (e.g. electronic, magnetic, and thermal) that are of fundamental importance to many technological applications, such as energy conversion, chemical analysis, biomedicine, optoelectronics, communication, and radiation detection.
CH3NH3PbBr3 perovskite nanocrystals (PNCs) of different sizes (ca. 2.5–100 nm) with high photoluminescence (PL) quantum yield (QY; ca. 15–55 %) and product yield have been synthesized using the ...branched molecules, APTES and NH2‐POSS, as capping ligands. These ligands are sterically hindered, resulting in a uniform size of PNCs. The different capping effects resulting from branched versus straight‐chain capping ligands were compared and a possible mechanism proposed to explain the dissolution–precipitation process, which affects the growth and aggregation of PNCs, and thereby their overall stability. Unlike conventional PNCs capped with straight‐chain ligands, APTES‐capped PNCs show high stability in protic solvents as a result of the strong steric hindrance and propensity for hydrolysis of APTES, which prevent such molecules from reaching and reacting with the core of PNCs.
Perovskite nanocrystals: Variously sized perovskite nanocrystals (PNCs) with high photoluminescence quantum yield and uniformity have been synthesized using branched ligands (APTES). APTES‐capped PNCs show high stability in protic solvents because the steric and hydrolysis properties of APTES prevent protic reactions with the core of PNCs.
This paper presents an investigation on the interstitial fluid pressure and stress reductions in a vascularized solid tumor using a thermal therapy approach. The solid tumor is modeled as a fluid ...infiltrated poroelastic medium with a pressure source subjected to spatial heating. The distributions of temperature, interstitial fluid pressure, strains and stresses in a spherical tumor are obtained using a thermoporoelasticity theory in which the extracellular solid matrix and the interstitial fluid have different coefficient of thermal expansion (CTE). The numerical results for a solid tumor subjected to uniform spatial heating indicate that the CTE of the solid matrix of the tumor plays a crucial role in the reductions in the fluid pressure and effective stresses caused by the thermal therapy. The pore pressure and effective stresses are reduced when the CTE of the solid matrix is higher than that of the interstitial fluid. The reductions in fluid pressure and stresses may become significant depending on the difference between the CTEs of the solid matrix and interstitial fluid. The reductions reach the maximum at the tumor center and decrease with increasing radial distance from the tumor center. Finally, the thermally induced fluid flow is directed from the surface towards the center thereby potentially improving the microcirculation in the solid tumor.
•A thermoporoelasticity model is developed for vascularized solid tumors.•TIF pressure and velocity obtained for a solid tumor undergoing hyperthermia.•The thermal therapy reduces TIF pressure and effective stresses.•Effects of differential CTE between the solid and interstitial fluid are examined.•Higher CTEs of the solid matrix leads to larger reductions in TIF pressure.
Paracrine regulation of melanogenesis Yuan, X.H.; Jin, Z.H.
British journal of dermatology (1951),
March 2018, 2018-03-00, 20180301, Letnik:
178, Številka:
3
Journal Article
Recenzirano
Summary
Melanocytes are generally characterized by the basic ability of melanin synthesis and transfer to adjacent keratinocytes. This constitutes an individual skin phenotype and provides epidermal ...protection from various stimuli, such as ultraviolet irradiation, through a complex process called melanogenesis, which can be regulated by autocrine or paracrine factors. Recent evidence has revealed the paracrine effects of keratinocytes on melanogenesis by secreting cytokines, including α‐melanocyte stimulating hormone and endothelin‐1. In addition to keratinocytes, there are other types of cells in the skin, such as fibroblasts and immune cells, which are also actively involved in the regulation of melanocyte behaviour through the production of paracrine factors. In addition, extracellular matrix proteins, which are secreted mainly by skin‐resident cells, not only play direct roles in regulating melanocyte morphology and functions but also provide structural support between the epidermis and dermis to control the distribution of various secreted cytokines from keratinocytes and/or fibroblasts, which are potentially involved in the regulation of melanogenesis. Moreover, understanding the origin of melanocytes (neural crest cells) and the presence of nerve endings in the epidermis can reveal the intimate contact between melanocytes and cutaneous specific nervous system proteins. Melanocytes are associated with all these networks with corresponding receptors expressed on the cell surface. In this review, we provide an overview of recent advances in determining the intimate relationships between melanocytes and their surrounding elements, which provide insights into the complex nature of the regulation of melanogenesis.
What's already known about this topic?
Melanogenesis, a complex biological process with different stages between epidermal melanocytes and keratinocytes, regulates skin pigmentation by various autocrine and paracrine effects.
What does this study add?
We provide an overview of paracrine effects on melanogenesis in consideration of various components surrounding melanocytes, including different types of cells, extracellular matrix and the nervous system in the skin.
Plain language summary available online
We report the synthesis and photoelectrochemical (PEC) studies of TiO2 nanoparticles and nanowires simultaneously doped with nitrogen and sensitized with CdSe quantum dots (QDs). These novel ...nanocomposite structures have been applied successfully as photoanodes for PEC hydrogen generation using Na2S and Na2SO3 as sacrificial reagents. We observe significant enhanced photoresponse in these nanocomposites compared to N-doped TiO2 or CdSe QD sensitized TiO2. The enhancement is attributed to the synergistic effect of CdSe sensitization and N-doping that facilitate hole transfer/transport from CdSe to TiO2 through oxygen vacancy states (Vo) mediated by N-doping. The results demonstrate the importance of designing and manipulating the energy band alignment in composite nanomaterials for fundamentally improving charge separation and transport and thereby PEC properties.
Hybrid semiconductor nanomaterials (HSNs) possess unique and interesting optical properties and functionalities that find important applications in emerging technologies. Compared to single component ...nanomaterials, hybrid nanomaterials offer the possibility and flexibility to control their properties by varying the composition of the materials and related parameters such as morphology and interface. Hybrid nanomaterials are essentially composite materials with relevant physical dimensions for the interface region between different components on the atomic up to nanometer scales, the same length scale of nanomaterials. This article provides an overview of some of the fundamental optical properties of hybrid semiconductor nanomaterials as well as their exploitation for potential applications in different fields. A number of examples from recent research are discussed to illustrate the points of interest and to highlight the salient features of HSNs.
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