quantum dots
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The document describes the preparation of cadmium telluride (CdTe) quantum dots through a 6 step process involving the addition of precursors, capping agents, and reducing agents. It examines the effects of varying concentrations of hydrazine hydrate on the size and emission of CdTe quantum dots. Finally, it discusses purification of the quantum dots using 2-propanol and phase transfer of the quantum dots from an aqueous to organic phase using CTAB and toluene.
quantum dots
- 1. 1 3 2 4 5 6 7 8 9 Preparation of CdTe (Cadmium Tellurite) quantum dots 1. Addition of deionized water to a beaker. 2. Introduction Cadmium chloride as a Cadmium precursor 3. Addition of capping agent : 3-MPA, 2- MEtOH, Glutathione 4. Introduction of Sodium Tellurite as a Tellurium precursor. 5. Addition of 2 to 3mg of Sodium borohydride (reducing agent). 6. Addition of Hydrazine hydrate (growth medium). 7. QD in visible light, QDs in UV light at 0h (8), after 2h (9). 3-MPA : 3-Mercaptopropanoic acid gives ¨C COOH group 2-MEtOH: 2-Mercaptoethanol gives ¨C OH group Quantum Dot Nano-crystal
- 2. A B C D E F G Effects of Hydrazine hydrate (N2H4) concentration on size and emission of the CdTe quantum dots A. 1M N2H4 B. 3M N2H4 C. 5M N2H4 D. 7M N2H4 E. 9M N2H4 F. 15M N2H4 G. 20M N2H4The nano-crystals are purified using 2-propanol A. Solution prior to addition of 2-propanol B. The quantum dots are precipitated at the bottom of the solution, they can be centrifuged at 13000 rpm and re-dispersed in deionized water (seen below) Purification of quantum dot nano-crystals A B Absorbance and emission of quantum dots under UV-Vis spectrophotometer and fluorescence spectrophotometer Colour Abs (nm) Emission (nm) Green 227 510 to 538 Yellow 234 550 to 565 Orange 240 587 to 610 Red 242 665
- 3. Phase transfer reaction of quantum dots ¨C From aqueous to organic phase Quantum dot nano-crystals in aqueous phase as seen under UV light Initiation of phase transfer using CTAB and Toluene Completion of phase transfer from aqueous to organic phase Quantum dot nano-crystals in toluene phase as seen under UV light COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO- COO - COO - COO- COO- COO- COO- COO- COO- CTA+ reacts with the carboxyl group on the quantum dots and helps facilitate the phase transfer Addition of toluene moves the quantum dots to organic phase A A B B C C