Time-dependent growth of silica shells on CdTe quantum dots
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Date
2018-06-16
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Mark
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MDPI
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The purpose of this study is to investigate the time dependent growth of silica shell on CdTe quantum dots to get its optimum thickness for applications in practice. The core/shell structured silica-coated CdTe quantum dots (CdTe/SiO2 QDs) were synthesized by Ströber process which used CdTe QDs co-stabilized by mercaptopropionic acid. The coating procedure used silane primer (3-mercaptopropyltrimethoxysilane) in order to make the QDs surface vitreophilic. The total size of QDs was dependent on the time of silica shell growth in the presence of sodium silicate likewise on the presence of ethanol during this growth. The size of particles was monitored during the first 72 hours using two principally different methods: Dynamic Light Scattering (DLS), and Scanning Electron Microscopy (SEM). The data obtained by both methods were compared and reasons of differences discussed. Without ethanol precipitation, the silica shell thickness grew slowly and increased the nanoparticle total size from approximately 23 nm up to almost 30 nm (DLS data) and up to almost 60 nm (SEM data) in three days. During the same time period but in ethanol presence, the size of CdTe/SiO2 QDs increased more significantly up to 115 nm (DLS data) and up to 83 nm (SEM data). The variances occurring between silica shell thickness caused by different ways of silica growth as well as by different evaluation methods were discussed.
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en