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Core-shell Semiconducting Nanoparticles Akcook8 (talk) 19:42, 22 September 2011 (UTC) Amanda you are so fast :) -Hyuck Jin Lee, beckhamlee (talk)Its 4 37pm. signing in Myj8 (talk) 21:23, 22 September 2011 (UTC)

A representation of core-shell nanocrystals
File:QD coloration.JPG
Core shell semiconductor nanocrystal coloration – photoluminescence of chloroform solutions of different QD types.

Core-shell semiconducting nanocrystals (CSSNCs) are a class of materials which have properties intermediate between those of small, individual molecules link neededand those of bulk, crystallinelink needed semiconductorslink needed. They are unique because of their easily modular properties, which are a result of their size. These nanocrystals are composed of a quantum dot core and a shell of a distinct semiconducting material. The core and the shell are typically composed of type II–VIlink needed, IV–VIlink needed, and III–Vlink needed semiconductors, with configurations such as CdS/ZnS, CdSe/ZnS, CdSe/CdS, and InAs/CdSe (core/shell)[1] The shell not only provides protection against environmental changes and photo-oxidativelink needed degradation, but also increases room temperature quantum yield and provides another route for modularity[2][3]. Precise control of the size, shape, and composition of the core and shell enable the emissionlink needed wavelengthlink needed to be tuned over a wider range of wavelengths than with either individual semiconductor. These materials have found applications in biological systems[4][5]. Core-shell nanocrystals are also found in nature, as seen in particles with a metal core and an oxidized shell.citation needed

Background

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This section is unclear until the very end between the differences of core-shell nanoparticles and quantum dots. It should be rearranged in order to help clarify the differences. Colloidallink needed semiconductor link needednanocrystalslink needed, which are also called quantum dots, consist of ~1-10nm diameter semiconductor nanoparticles that have organic ligands bound to their surface. These nanomaterials have found applications in nanoscale photoniclink needed, photovoltaiclink needed, and light-emitting diode (LED)link needed devices due to their size-dependent opticallink needed and electroniclink needed properties. Quantum dots are popular alternatives to organic dyeslink needed as fluorescentlink needed labelslink needed for biological imaginglink needed and sensing link neededdue to their small size, tuneable emission, and photostability link needed.

The luminescentlink needed properties of quantum dots arise from exciton decay (recombination of electron hole pairslink needed) which can proceed through a radiativelink needed or nonradiative link neededpathway. The radiative pathway involves electrons relaxing from the conduction bandlink needed to the valence bandlink needed by emitting photons with wavelengths corresponding to the semiconductor's bandgap. Nonradiative recombination can occur through energy release via phonon emission link neededor auger recombinationlink needed. In this size regime, quantum confinement effects lead to a size dependent increasing bandgap with observable, quantized energy levelslink needed [2]. The quantized energy levels observed in quantum dots lead to electronic structures that are intermediate between single molecules which have a single HOMO-LUMO gap and bulk semiconductors which have continuous energy levels within bands[6]

The electronic structure of quantum dots is intermediate between single molecules and bulk semiconductors.

Semiconductor nanocrystals generally adopt the same crystal structure as their extended solids. At the surface of the crystal the periodicitylink needed abruptly stops, resulting in surface atoms having a lower coordination numberlink needed than the interior atoms. This incomplete bonding (relative to the interior crystal structure) results in atomic orbitals link neededthat point away from the surface called "dangling orbitals" or unpassivated orbitals[7]. Surface dangling orbitals are localized and carry a slight negativelink needed or positive link neededcharge. Weak interaction among the inhomogeneouslink needed charged energy states on the surface has been hypothesized to form a band structure[8]. If the energy of the dangling orbital band is within the semiconductor bandgap, electrons and holes can be trapped at the crystal surface. For example, in CdSe quantum dots, Cd dangling orbitals act as electron traps while Se dangling orbitals act as hole traps. Also, surface defects in the crystal structure can act as charge carrier traps.

Charge carrier trapping on QDs increases the probability of non-radiative recombinationlink needed, which reduces the fluorescence quantum yield. Surface-bound organic ligands are typically used to coordinate to surface atoms having reduced coordination number in order to passivate the surface traps. For example, tri-n-octylphosphine oxide (TOPO) and trioctylphospine(TOP) have been used to control the growth conditions and passivate the surface traps of high quality CdSe quantum dots. Although this method provides narrow size distributions and good crystallinity, the quantum yields are ~5-15% [9]. Alkylamines have been incorporated into the TOP/TOPO synthetic method to reach quantum yieldslink needed of ~50%. [10]

The main problem with using organic ligands for quantum dot surface trap passivation is the difficulty in simultaneously passivatingboth both anionic and cationic surface traps. Steric hindrancelink needed between bulky organic ligands results in incomplete surface coverage and unpassivated dangling orbitals. [3] Growing epitaxial inorganic semiconductor shells over quantum dots inhibits photo-oxidation and enables passivation of both anionic and cationic surface trap states [8]. CdSe/CdS and ZnSe/CdSe nanocrystals have been synthesized that exhibit 85% and 80-90% quantum yield, respectively [11][12].Could the quote be eliminated and replaced with a suitable paraphrase or summary?

Core-shell semiconductor nanocrystal architecture was initially investigated in the 1980's, followed by a surge of publications on synthetic methods the 1990's [2].

Classification of core-shell semiconductor nanocrystals

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Core shell semiconductor nanocrystal properties are based on the relative conduction and valence band edge alignment of the core and the shell. In type I semiconductor heterostructures, the electron and holes tend to localize within the core. In type II heterostructures, one carrier is localized in the shell while the other is localized in the core.

The three types of core-shell nanocrystals. The upper and lower edges represent the upper and lower energy edges of the core (blue) and the shell (red).
Type I core shell semiconductor nanocrystal (CdSe/CdS) band-edge alignment. VB=valence band, CB=conduction band

Type I

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  • Description

In a Type I CSSNC, the bandgaplink needed of core is smaller than that of the shell. Both the conduction and valence band edges of the core lie within the bandgap of the shell, which confines both electrons and holes in the core. This can be seen in figure X, where the electron and hole of an exciton at the CdSe(bandgap:1.74 eV)/CdS(bandgap:2.42 eV) interface occupy energy states within the CdSe core, which corresponds to the lowest available energy separation. The emission wavelength due to radiative electron-hole recombination within the core is slightly redshiftedlink needed (bathochromic shift) compared to uncoated CdSe.

  • Examples

CdSe/CdS, CdSe/ZnS,and InAs/CdSe [2]

Reverse Type I

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In the reverse type I configuration, the core has a wider bandgap than the shell, and the conduction and valence band edges of the shell lie within those of the core. The lowest available exciton energy separation occurs when the charge carriers are localized in the shell. Changing the shell thickness tunes the emission wavelength.

  • Examples

CdS/HgS, CdS/CdSe,and ZnSe/CdSe[2]

Type II

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  • Description

In the type II configuration, the valence and conduction band edge are both lower or higher than the band edges of the shell. An example of a type II is shown in figure X, ZnTe(bandgap:2.26units?)/CdSe(bandgap:1.74units?). The lowest energy separation of the electron and the hole will occur when the hole is confined in the ZnTe core valence band and the electron is confined in the CdSe shell conduction band. The emission wavelength will be determined by the energy difference between these occupied states, as shown by the red arrow, which will be at a lower energy than either of the individual bandgaps[13]. The emission wavelength can be significantly red shifted compared to the unpassivated core.

Type II core shell semiconductor nanocrystal (ZnTe/CdSe) band-edge alignment. Red arrow shows emission energy. VB=valence band, CB=conduction band
  • Examples

ZnTe/CdSe, CdTe/CdSe, CdS/ZnSe [14]

Doped Core Shell Semiconductor Nanocrystals

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Dopinglink needed has been shown to strongly affect the optical properties of semiconductor nanocrystals. [15] Impurity concentrations in semiconductor nanocrystals grown using colloidal synthesis, however, are typically lower than in their bulk counterparts. [16] There has been interest in magneticlink needed doping of CSSNCs for applications in magnetic memorylink needed and spin-based electronicslink needed (spintronics?) [17] Dual-mode optical and magnetic resonance (MR) imaging link needed (MRI?) has been explored by doping the shell of CdSe/ZnS with Mn, which caused the CSSNC to be paramagneticlink needed [18]

Synthesis

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It might be best to move this section before the different types of core shell nanoparticles are discussed as the naming convention is explained in this section. To synthesize core shell nanoparticles, scientists have studied and found several methods such as chemical precipitation, sol-gel, microemulsion and inverse micelles. Those methods have been used to grow core shell chalcogenide nanoparticles with an emphasis on better control technique on size, shape and size distribution[19]. To control the growth of nanoparticles, supporing matrices such as glasseslink needed , zeoliteslink needed , polymerslink needed or fatty acidslink needed with tunable optical properties have been used[19]. In addition, to prepare the quantum size nanoparticles of sulfideslink needed , selenideslink needed and tellurideslink needed , Langmuir-Blodgett technique has been invested and used[19].

Also, core shell quantum dot semiconductor nanostructures can be grwon by using collodial chemistry methods, with an appropriate handling of the reaction kineticslink needed [20]. Using this method with a relatively high control of their size and shapes, scientists could get the semiconductor nanostructures in the form of dots, tubes, wires and other forms which can show rather interesting optic and electronic size dependent properties[20]. Since the synergistic properties induced by the intimate contact and the interaction between different components, core and shell, core shell nanoparticles can provide novel functions which are not provided in the single nanoparticles and have enhanced properties[21].

Usually, when the core shell nanoparticles(or nanocrystals) shows the "Core material/Shell material" form. For example, CdSe/CdS core shell nanocrystals mean that CdSe is core and CdS coats CdSe and make a shell on the surface of CdSe. The size of core materials and the thickness of shell can be determined during synthesis. For the synthesis of CdSe core nanocrystals, the volume of H2S gas can determine the size of core nanocrystals. The volume of H2S increases, the size of core decreases[11]. Or, as soon as the reaction solution reaches the desired temperature to react, make the solution cool really fast, the size of core can be smaller[12]. In addition, the thickness of shell is determined by the added amount of shell material during the coating process[12].

Characterization

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An increase in either the core size or shell length results in longer emission wavelengths. The interface between the core and shell can be tailored to passivate relaxation pathways and form radiative states. The size dependence of band gap in these nanoparticles due to quantum confinementlink needed effect has been utilized to control the photoluminescence color from blue to red by preparing nanoparticles of different size[22]. By manipulating the size or shape of the nanoparticles, the luminescence colors and the purity of it can be controlled[22]. But, the quantum yield or the brightness of luminescence of nanoparticles is ultimately limited and it cannot be controlled, because of the presence of surface traps[22]

In addition, by using UV-vis link needed absorption spectra, X-ray diffraction (XRD)link needed , transmission electron microscopy (TEM)link needed and X-ray photoelectron spectroscopy (XPS)link needed , synthesized core/shell nanocrystals can be identified and charaterized.


The Synthesis sections contains in depth synthesis techniques which resemble the experimental section of a paper. This not appropriate for a wikipedia article or a review article. This section should be summarized in only include the important highlights of the method.

Type I - Synthesis of CdSe/CdS[11]

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1. Chemicals

Toluene, Methanol, n-Hexane, Chloroform, Cadmium acetate, Selenium, bios(trimethyl-silyl)sulfide, n-Octylphosphonic acid (OPA), n-tetradecylphosphonic acid(TDPA), H2S gas Tri-n-octylphosphine (TOP), Tri-n-octylphosphine oxide (TOPO), Hexadecylamine (HDA)

2. Synthesis of CdSe nanocrystals in a HDA-TOPO-TOP-TDPA mixture

In order to synthesize, every substances should be dried and water-free condition. First, 8g of TOPO should be dried and and degassed under vacuum and maked it be cooled to around 120℃. Then, adding 0.5g of HDA and 0.15g of TDPA and keep drying at 120℃ under vacuum. Add TOP-Se solution(1.0M of 2 ml of solution, Se is dissolved in TOP) into the mixture before and heat it to 300℃. Cadmium stock solution(0.12g of cadmiun acetate in 3 ml of TOP) shold be quickly injected under vigorous stirring, resulting in nucleation of CdSe nanocrystals.

3. Synthesis of CdSe/CdS core-shell nanocrystals by injecting H2S gas

The freshly crude solution of CdSe from the previous step would be heated to to 140℃. Using a Hamilton syringe, injecting in 2 ml portions of (~1 ingection per 10-15minutes) H2S gas slowly through septum without making any bubbles in the solution. The amount of injecting H2S gas is dependent on the size of the CdSe cores. The size of CdSe increases, less amount of H2S should be injected. The reaction mixture absorbs H2S gas during stirring at 140℃, and about an hour later, it wolud be cooled to 100℃. Another an hour later with stirring, it shold be cooled again to around 50℃. During cooling the solution, 15 ml of chlorofrom must be added in order to prevent solidification of TOPO and HDA. Reaction mixture becomes slightly turbid with some white solid which is unreacted cadmium acetate after it cools down to room temperature. Then, filter the mixture through a PTFE 0.2µm syringe filter. Then, highly luminescent CdSe/CdS nanocrystals can be isolated from the crude solution by precipitating them with methanol. by filterated or centrifuged the mixture, CdSe/CdS nanocrystals can be obtained and the precipitate can be redissolved in chloroform or toluene.

Reverse Type I - Synthesis of ZnSe/CdSe [23]

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1. Chemicals

Octadecylamine, Se in trioctylphosphine (TOP), ZnEt2, Octadecene (ODE), Oleylamine, CdO

2. Synthesis of ZnSe

5.0g of octadecylamine would be heated to 310℃ under Ar flow and when it reaches to 310℃, 0.3 mmol of Se in 2.0ml of trioctylphosphine should be added to the reaction flask. Then, inject 0.3 mmol of ZnEt2 in 1.0 ml of TOP into the reaction flask and stir the reaction mixture at 300℃ for 10 minutes. After 10 minutes, stop heating to terminate the reaction. After cooling down to about 70℃, dilute the reaction solution to 25.0 ml by adding octadecene, before solidification take place in the reaction flask. ZnSe can be obtained.

3. coating with CdSe

Mix 2.5 ml of crude ZnSe nanocrystals reaction solution (containing 0.03mmol of ZnSe), 4.5 ml of ODE and 0.5 ml of oleylamine and heat to 230℃. In addition, mix same amount of Cd and Se stock solutions (0.1M Se stock solution can be obtained by dissolving Se powder with TOP in ODE and 0.1M Cd stock solution can be prepared by dissolving CdO with 6-fold of oleic acid in ODE) and add dropwise to the vigorously stirred solution of ZnSe core nanocrystals via a syringe pump over a period of 2 to 3 hours.

Type II - Synthesis of CdS/ZnSe [12]

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1. Chemicals

Myristic acid, Tetraethylthiuram disulfide, 2,2'-dithiobisbenzothiazole, Cd(AcO)2⋅2H2O, Chloroform, Toluene, 1-Octadecene (ODE), Pyridine, Anhydrous hexane, Octadecylamine (ODA), Zinc oleate (Zn(AcO)2), tri-n-octylphosphine (TOP), Oleic acid, Acetone, Methanol

2. Synthesis of CdS nanocrystals

Put 0.266g (1mmol) of Cd(AcO)2⋅2H2O, 0.4567g (2 mmol) of myristic acid, 5.14 ml of 0.1M sulfur solution in ODE (0.514 mmol), 1.3 ml of 005ㅡ tetraethylthiuram disulfide solution in ODE (65 μmol) and 2,2'-dithiobisbenzothiazole (192 μmol) in a flask and mixed with 30 ml of ODE. After heating it in a vacuum for an hour at 120℃, filled reaction flask with nitrogen gas and reheating slowly to 240℃. Around 240℃, the solution turns into dark yellow. Also, by recording UV-vis and PL spectra of growth solution, the particl size can be monitored. When the particle size reaches to the desired size, the growth solution would be cooled down and washed twice with chloroform and toluene in order to remove byproducts from the reaction or free ligands. The synthesized CdS particles are not soluble in both solvents.

3. Purification of Cds nanocrystals with pyridine

To ensure that there is no Cd(II) on the surface of CdS from the previous step, it need to be purificated. Using acetone, precipitating and washing CdS nanocrystals and then the solvent was removed in vacus and 5-10ml of pyridine would be added to precipitated, which is dried CdS nanocrystals. To dissolve CdS in pyridine entirely, heated to around 50℃ and keep the temperatrue for about 12hours. CdS nanocrystals would be precipitated from pyridine with water, redissolved in acetone and reprecipitated with water to purificated. After that, washing those CdS nanocrystals and dissolving in hexane to be coated with ZnSe.

4. Overcoating with ZnSe

Dissolve 20 mg of CdS nanocrystals in hexane and inject this solution into a degassed misture of ODA (1.5g) and ODE (6ml) at 120℃. Then, place the solution under a vacuum for about 30 minutes to remove hexane and heat the solution to 220-240℃ under N2 atmosphere. By mixing 0.1M of Zn(AcO)2 in TOP with the equivalent amount of oleic acid, zinc oleate in TOP can be prepared. That zinc oleate solution and Se solution in TOP should be mixed with stoichiometric amount and add the mixed solution to the CdS nanocrystals dropwise. During Zn/Se solution addition, the color of solution changes from lemon-yellow to red. After the addition, the mixture should be cooled to 150-170℃ and it should be annealed at this temperature for 24-48hours to increase quantum yield of CdS/ZnSe core shell nanocrystals. When the annealing is over, the mixture should be cooled again to 80-90℃ and CdS/ZnSe nanocrystals are precipitated with acetone. Centrifuged the solution then the product should be washed with methanol and acetone to purify.

Applications

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One of the most important properties of core-shell semiconducting nanocrystals (CSSNCs) is that their cores, which are quantum dots, fluoresce, which is important in their biomedical and optical applications. The shells are highly modular, and thus the bulk properties, such as solubilitylink needed and activity of the CSSNSs can be changed.

Biomedical Applications[24][25][26][27]

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The properties desired of CSSNCs when using them for biological applications include high quantum yield, narrow fluorescence emission, broad absorption profile, stability against photobleaching, 20 second fluorescent lifetime, and high brightness. High quantum yields mean that minimal energy will need to be put into the quantum dot to induce fluorescence. A narrow fluorescence emission allows for multiple colors to be imaged at once without color overlap between different types of CSSNCs. Having a broad absorption profile allows multiple CSSNCs to be excited at the same wavelength and thus, multiple CSSNCs could be imaged simultaneously. Having a 20 second fluorescent lifetime allows for time-resolved bioimaging. The utility of CSSNCs is that they can be a complement to organic fluorophores. CSSNCs are less susceptible to photobleaching link needed , but less is known about them compared to organic fluorophores link needed. CSSNCs have 100-1000 times the two-photon fluorescence efficiency as organic dyes, exemplifying their value.

In the cases where CSSNCs are used in biological medium, the core is a quantum dot and the shell can be an organic molecule or biological ligands, such as a DNA link needed, that are used for biocompatibility link needed and targeting. The shell can also be an organic molecule to which a biological molecule is later conjugated, furthering the modularity of core-shell structure. The most popular core/shell pair used is CdSe core with ZnS or CdS shell, which improves the quantum yield and protects against photobleaching compared to that of the core material alone. The size of the CSSNC is directly correlated to the color of fluorescence, so being able to control particle size is desirable. However, it is generally unknown how the shell molecules, and salt concentration, pH link needed, and temperature link neededof the media affect the CSSNCs’ properties and remains empirical link needed.

In Vitro Cell Labeling
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The pathway of the cells movement can be seen by the absence of CSSNCs
The pathway of the cells movement can be seen by the absence of CSSNCs

You shouldn't start a sentence with a preposition, try rearranging the sentence to avoid this. Because multiple colors can be imaged, CSSNCs’ ability to be used in cell labeling is of growing importance. However, it can be difficult to get CSSNSs across the cell membrane link needed. This has been achieved via endocytosis (the most common method), direct microinjection, and electroporation, and once in the cell, they become concentrated in the nucleus and can stay there for extended periods of time. Once CSSNCs are inside cells, they remain even after cellular division and can be imaged in both mother and daughter cells. This particular technique was shown using Xenopus link neededembryos link needed. Another example of CSSNCs is seen in their tracking ability; when cells are gown on a 2D matrix embedded with CSSNSs, cells uptake the CSSNSs as they move, leaving a trail seen as the absence of CSSNSs. This means that the mobility of cells can be imaged, which is important since the metastatic potential of breast tissue cells has been shown to increase with mobility. Also, it has been shown that five different toxins can be detected using five different CSSNSs simultaneously. In a move toward more environmentally-friendly and less toxic CSSNCs, Si quantum dots with various shells have been developed. Si is 10 times safer than Cd and current work is focused on making Si more water soluble and biocompatible. In particular, Si quantum dots with poly(acrylic acid) and allylamine shells have been used in cell labeling. Other in vitro uses include flow cyclometry link needed, pathogen link needed detection, and genomic link needed and proteomic link needed detection.

In Vivo and Deep Tissue Imaging
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Because CSSNSs emit in the near-infrared link neededregion (700-900 nm) of the electromagnetic spectrum, imaging them is not complicated by autofluorescence of tissue, which occurs at higher frequencies (400-600 nm), and scattering effects. This has been used in the mapping of sentinel lymph-nodes link needed in cancer surgery in animals. Lymph nodes 1 cm deep were imaged and the excised nodes with CSSNS accumulation were found to have the highest probability for containing metastatic cells. In addition, CSSNSs have been shown to remain fluorescent in cells in vivo for 4 months. To track and diagnose cancer cells, labeled squamous carminoma link needed cell-line U14 cells were used and fluorescent images could be seen after 6h. CSSNSs conjugated to doxorubicin were also used to target, image, and sense prostate cancer cells that express the prostate-specific membrane antigen protein. Using a cancer-specific antibody conjugated to QDs with polymer shells is the most popular in tumor targeted imaging. The main disadvantage of using CSSNSs for in vivo imaging is the lack of information about their excretion and toxicity. The typical cores used show DNA damage and toxicity toward liver cells, but using shells seems to diminish this effect. The use of other substances in the core, such as rare-earth elements and Si, are being explored to reduce toxicity. Other disadvantages include limited commercial availability, variability in surface chemistry, nonspecific binding, and instrument limitation.

Optics [24]

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The size, shape, and composition of the core-shell structure are related to the bandgap, which in turn is related to its optical properties. Thus, by modulating the size, shape, and material of the core, the optics can be tuned and optimized for use in optical devices and applications such as LEDs, detectors, lasers, phosphors, and photovoltaics.

LEDs

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Currently, CSSNS LED efficiency is less than that of organic LEDs. However, studies show that they have potential to accomplish what organic LEDs cannot. CSSNS LEDs constructed using multiple layers of CSSNSs resulted in poor conduction, charge imbalance, low luminescence efficiency, and a large number of pinhole defects. LEDs constructed of one monolayer avoid these problems. An advantage of CSSNS LEDs over organic LEDs is that CSSNS LEDs have narrower emissions, as narrow as 32 nm, than organic LEDs, which range from 50-100nm. [28] Specifically, the core-shell motif is desirable for use in LEDs because of their electroluminescence link neededand photoluminescence link needed quantum efficiencies and their ability to be processed into devices easily. Current aims for LED displays include developing materials with wavelength emissions of 610–620 nm for red displays, 525–530 nm for green displays, and 460–470 nm for blue displays. This is because these wavelengths maximize the perceived power and they lie outside of the National Television System Committee link needed standard color triangle link needed. CSSNSs have been synthesized that meet these wavelength emissions: (CdSe)ZnS for red emission, (CdS)ZnS for blue emission, and (CdxZn1-xSe)CdyZn1-yS for the green emission. Using CdSe core and ZnS or CdS/ZnS shells, the maximum luminance values of red, orange, yellow and green LEDs were improved to 9,064, 3,200, 4,470 and 3,700 cd m-2, respectively; electroluminescent efficiency (1.1–2.8 cd A21), and turn-on voltages (3–4 V) were also increased.

Lasers

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In CSSNSs with only one exciton, absorption and stimulated emission occur equally and in CSSNSs with more than one exciton, non-radiative Auger recombination occurs, which decays optical gain, an important quality in lasers. However, type II CSSNSs, CdS/ZnSe, were used in optical amplification from stimulated emission of single-exiton states, eliminating Auger recombination. This has the advantage that lasing threshold could be lowered under continuous wave excitation, enhancing the potential of CSSNSs as optical gain media. Type II CSSNSs separate the electrons and holes of the exciton pair, which leads to a strong electric field and thus, reducing absorption losses. [29]

Phosphors

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By combining the modularity of CSSNSs and stability of organic polymer, a broad range of colors of phosphors were developed. CdSe core/ZnS shell CSSNSs are used to generate bluish green to red colors, and (CdS)ZnS QDs are used to generate violet to blue colors. By mixing the appropriate amounts of the different sizes of CSSNSs, the entire visible range with narrow emission profiles and high photoluminescence quantum yields can be achieved.[30]

References

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  23. ^ Zhong, X.; Xie, R.; Zhang, Y.; Basche, T.; Knoll, W. High-Quality Violet to Red Emitting ZnSe/CdSe Core/Shell nanocrystals Chem. Mater. 2005, 17, 4038-4042
  24. ^ a b Klostranec, J. M. (4 August 2006). "Quantum Dots in Biological and Biomedical Research: Recent Progress and Present Challenges". Advanced Materials. 18 (15): 1953–1964. doi:10.1002/adma.200500786. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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Peer Review

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The article so far gives a clear outline of the topic, with basic concepts and some background information to help people get familiar with the material. Also important reviews are cited. The followings are some suggestions to the review article.

1 The title is “Core-shell Nanoparticles” but the article describes core-shell semiconducting nanoparticles, one type of core-shell nanoparticles, thus the title need be changed to “Core-shell Semiconducting Nanoparticles”.

2 The terms FRET, electrochemiluminescence, fluorescence and biosensor should be cross-linked in Wikipedia.

3 Besides their unique properties, in the first paragraph, the extensive applications of core-shell semiconducting nanoparticles need be briefly stated, related to their properties, for the general public to realize the excitement and significance of the research field.

4 In the Background section, a history of modulated synthesis of core-shell semiconducting nanoparticles along with their specific properties need be briefly addressed. Then corresponding applications can also be discussed. Thus the relationship among structure, property and application is established and easy to understand, which will be discussed in details in the following paragraphs.

5 According to the outline, the classification of core-shell semiconducting nanoparticles may be combined with different synthesis methods.

6 Core-shell (quantum dots) QDs find vast applications because of numerous methods of functionalization, so Bio-functionalization of Core-shell QDs can be added a new category.

7 Drawbacks of this material need be added, for QDs, the toxicity is a great issue limiting their application. How people tried to overcome this problem need be pointed out.

8 Some categories in the Application section overlap. For example, biosensing, cell labeling, QD assay labeling and QD FRET overlap. Actually biosensing is a broad topic including QD-based electrochemistry, electrochemiluminescence and optical sensing methods, which generally use QD as a label and taking advantage of FRET. Besides, QDs have biomedical applications because of their great optical properties, thus the category Optics in Applications might also overlap with biomedical applications. The authors need to classify carefully the references according to the applications while continuing the article. Also, the authors should focus on core-shell QDs instead of normal QDs.

9 Band structures and spectra of core-shell QDs need be added as figures. How band structures relate to their unique electro/optical properties need be explained

10 Photos of core-shell QDs solutions with different colors can be added.

11 Schemes of bio-applications of core-shell QDs can be selectively added.

12 Some references repeat, like “Reiss, P; Protiere, M; Li, L. Core/Shell Semiconductor Nanocrystals. Small 2009, 5, 154-168”.

13 Numerous researches are done in this field, so newest research papers may be cited before completing the review.

14 The sentences in the first paragraph and the Background need be more logically connected and paragraphs in Background need to be more well-organized with logic.
--Lengmartin (talk) 22:01, 8 October 2011 (UTC)


Peer Review


1) The title captures a thematic area of materials science appropriate for an encyclopedic website. The overall title of “Core-shell nanoparticles” encompasses a wide range of types of particles, but I believe a subset, “Core-shell semiconducting nanocrystals”, was defined, which is more appropriate. Another concern with the title is that it appears that some researchers apply the term “semiconducting nanocrystals” to other shapes, such as “nanorods”. If it is the intention of the group to address these materials, it should be further somewhere in the general introduction or background.

2) The general summary may be written at a higher level than is normally seen in Wikipedia entries.

3) There is a sufficient start on background and significance, but more could be added. The background information could begin with a brief history/explanation of the quantum dot and what motivated research to move into core-shell semiconducting nanocrystals. When discussing the history of research in this field, a few of the review articles could be cited. Specific examples could be mentioned in the history section, such as the first type of core-shell nanocrystal studied.

The significance portion could be strengthened by a discussion of the advantages of these materials for the applications that will be discussed later in the article in depth.

4) The outlined areas make sense and are in a logical order. I might suggest a section on future work, i.e. where research is currently headed.

5) The figures add to the understanding of the topic at hand, but I feel that more figures could be added. A more comprehensive band diagram, such as one of a single type of core-shell particle, may help further explain the unique properties. If open source figures could be found, a TEM image would be beneficial. A basic visualization of size/property relationship is the common image of different color solutions of different size semiconductor nanocrystals. This type of image may help explain the significance of these materials to a non-technical reader.

6) A review of literature shows that the authors have done a good job in citing influential articles and reviews since 2008. Since the site will be on Wikipedia, some textbook and/or website references would be useful to the general public.

7) The introduction could be re-written with a more regard to the audience it is intended before. Specifically, this sentence: “In a Type II semiconductor nanocrystal, the core has a lower band gap and a lower energy valence band than the shell, or both band gap and valence band are higher than those of shell, that leads to a situation in which one carrier is mostly confined to the core, while the other is mostly confined to the shell.” is confusing to the reader.


Na9234 (talk) 04:22, 13 October 2011 (UTC)

Peer Review

1. The authors might want to use the title “Core-shell semiconducting nanocrystals” instead of “Core-shell Nanoparticles”.

2. There are several words that have related sites. For instance, semiconductor, nanocrystal, electron, charge carrier, photoluminescence, emission wavelength, relaxation etc.

3. The general public summary is written at an appropriate level.

4. The authors could add more about the significance of core-shell semiconducting nanocrystals in the background part. A brief but comprehensive introduction about nanocrystal application would be nice.

5. “Also, core shell quantum dot semiconductor nanostructures can be grwon by using collodial chemistry methods, with an appropriate handling of the reaction kinetics[10].” is unexpected.

6. Overall, the contents are organized and in a logical order. However, the application might require a bit more thought since quantum dots have both bio and optic applications. From my understanding, the bio applications the authors referred to are based on the nanoparticles’ optic characteristics.

7. The authors should consider adding the drawbacks and efforts already done to address them.

8. I would suggest addition of pictures illustrating the applications.

9. There is one publication being repeatedly listed for several times—“ Reiss, P; Protiere, M; Li, L. Core/Shell Semiconductor Nanocrystals. Small 2009, 5, 154-168”.

10. I would refer to some publications talking about the synthesis and characterization etc.

11. To sum up, the language used is easily understood. The authors might want to organize the background part and application part more logically. The background part could use such arrangement—history, properties, common synthetic methods, applications etc.
Looooker (talk) 8:50, 13 October 2011 (UTC) 1) Does the title capture a thematic area of materials science appropriate for an encyclopedic Wikipedia site? Are there related sites the author s have not linked to so far? Provide list. The title does capture an area appropriate for Wikipedia. There are several sections where there are little to no links to other Wikipedia sites as I indicate in red text above. 2) Is the general public summary written at the appropriate level? Does it effectively capture the subject of the review? Yes, it provides a brief overview for somebody who might not have an idea of what Core-shell Semiconducting Nanoparticles are 3) Does the Background and Significance explain to the reader why this area is important? Does it provide sufficient background to place the topic in the context of the field of materials science? The background section is confusing as it talks only about quantum dots at first and then at the very end relates to the core-shell semiconducting nanoparticles. This obstructs the significance of core-shell semiconducting nanoparticles. This section needs to be revised in order to clear up the significance and relate core-shell semiconducting nanoparticles to quantum dots. 5) Do the figures add substantially to enhancing the explanation of the topic? Are there key figures missing that you believe would be useful? If you recommend changes, be specific. The figures are well drawn and demonstrate the text of the articles very well. Some changes that could be made is the modification of figure 1 and figure 4 to have the same color coding for the core and the shell. The synthesis section could be helped out by schematic figures demonstrating the synthetic techniques. 6) Are there major papers in the field missing in the references? Be specific. Most of the references are fairly recent and a quick Scifinder and Google scholar search does not show any obvious missing major papers. 7) Overall, is the language used effective and easily understood. Flag all confusing sections and/or offer suggestions for rewording. See in text for most comments. The only other comment I have is that the references are not cited properly though out the paper. Instead of citing in the reference headers you should cite directly after using the ideas/content from the paper at the end of the sentence. Look at other Wikipedia articles to see examples of this. Nbx909 (talk) 23:31, 29 November 2011 (UTC)

new

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