Synthesis & Characterization Of Cd Se Nanocrystals Doped With Co2+ Ions

2982 words - 12 pages

Introduction
In the past two decades, semiconductor nanocrystals (NCs) have been got a great deal attention by several research groups worldwide. Because of their unique properties (i.e. Optical, and electronic properties) [1-9], which leading it to open new opportunities and to be considered as a good candidate to be used in so many different applications (i.e. Biomarker, medical imaging, critical components in electronic devices, lasers, LED, solar cells, etc...) [10-15].
Engineering the quantum dots (QDs) by incorporation of impurities into the QDs host crystal is one of the main routes to use QDs into several technological applications (i.e. including magnetic, optoelectronic, and ...view middle of the document...

Several efforts have been focused to find a new route to enhance and improve the incorporation of magnetic impurities from TM2+ ions [27, 30-34]. To date, solution synthesis of high-quality magnetic doped QDs has been limited to group II-VI chalcogenides (i.e. CdS, CdSe, ZnS, and ZnSe). Bryan and Gamelin concluded from the previous studies the reasons for the tendency of dopant ions to be excluded during NCs synthesis [23], as following: (i) surface-bound dopants may have different geometries, and (ii) ligation. Finally, exchange coupling interactions with the semiconductor band electrons than substitutionally incorporated dopants have. The target physical properties of the DMS may therefore be compromised if care is not taken to ensure substitutional doping [23]. In 2008; Du et al. demonstrated that in their model (i.e. T rapped Dopant Model) that surfactants, which are used to control nanocrystals growth, play another important role by affecting doping in two ways. The first one is focused on the competition between surfactant and the nanocrystal surface by binding impurity atoms, while the second way is based on the influence of surfactant on the solubility of impurities in the growth solution, unless extrinsic factors preempt this effect [35].
Many approaches have been carried out to prepare colloidal doped semiconductor NCs. For example, hot injection methods have been used to synthesize colloidal Mn2+ doped CdSe [30,36-39], ZnSe [20,40-42], and PbSe [23] colloidal NCs. Colloidal ZnO DMS–NCs doped with Co2+, Ni2+, and Mn2+ have been prepared by low-temperature hydrolysis and condensation [21,43-47]. Sol–gel methods have been used to prepare colloidal doped TiO2 NCs [48-50]. Also, doped II–VI sulfide DMS QDs [51-62], and rare earth doped sulfide semiconductor NCs [63,64]. A high-temperature pyrolysis of was used to synthesize Co2+- and Eu3+- doped CdSe NCs [25,31,65]. Autoclaving has occasionally been used to induce crystallization at lower temperatures than reached under atmospheric pressures while retaining colloidal properties, for example in the preparation of colloidal doped SnO2 [23,52,66-69, 27] and InAs NCs [24].
In this work, we proposed and improved the doping of semiconductor QDs by TM2+ ions (i.e. Co2+ ions) impurities. This method is based on using organic ligand compound as a secondary precursor for magnetic ions which has to decompose slowly in the same temperature range as Cd2+ precursor does. This organic ligand complex will act as a source for the dopant, which will be released gradually during the reaction in order to replace few Cd2+ ions in CdSe nanocrystals (NCs).

Works Cited

1. Bawendi, M.G., Steigerwald, M.L., Brus, L.E.; the quantum-mechanics of larger semiconductor clusters (quantum dots), Ann. Rev. Phy. Chem. 41 (1990) 477
2. Alivisatos, A.P., perspectives on physical chemistry of semiconductor nanocrystals, J. Phys. Chem. 100 (1996) 13226
3. El-Sayed, M.A., small is different: shape-, size-, and...

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