Influence of Acid on Luminescence Properties of Thioglycolic Acid-Capped CdTe Quantum Dots

• Published in: Journal of physical chemistry. C Vol. 112; no. 22; pp. 8244 - 8250
• Main Authors: Mandal, Abhijit, Tamai, Naoto
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05.06.2008
• Subjects: C: Nanops and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp801043e

CdTe quantum dots (QDs) were prepared in aqueous solution by the reaction between Cd2+ and H2Te in the presence of thioglycolic acid (TGA) as a stabilizer. In order to improve the quantum yield (QY), we systematically optimized the synthesis conditions and found that the pH value significantly affected the optical properties of CdTe QDs. After synthesizing different sizes of CdTe QDs, we have extended our observation to check the effect of pH level on different sizes of CdTe QDs. Experimental results reveal that the luminescence QY as well as the lifetime of TGA-capped CdTe QDs increased noticeably when the solution was made acidic up to a certain pH level. This observation is much more pronounced in the case of smaller size QDs. The optical spectroscopy studies imply that the pH-dependent behavior of the luminescence of CdTe QDs is caused by structural changes on the surface rather than the size of the QDs. Turbidity observed at low pH indicates the formation of aggregates of QDs. This is confirmed by steady-state spectroscopy and atomic force microscopy studies. We observed that both the luminescence intensity and absorbance changes were reversible when the pH level of the solution was brought back its original value.