Colloidal CdTe and CdSe Quantum Dots: Technology of Preparing and Optical Properties

The technology for preparing colloidal CdTe quantum dots (QDs) in an alcaline medium in the presence of passivators thioglycolic acid (TGA) and L-cysteine (L-cys) as well as the technology for preparing colloidal CdSe QDs by method of the reverse micelles is presented. The CdTe QDs were synthesized at different technologic conditions in an aqua colloidal solutions as well as in a polymeric matrix of poly(diallydimethylammonium chloride). For synthesis of CdSe QDs in microemulsion system Triton X-100 and n-hexyl alcohol were used. Cyclohexane served as a non-polar phase, water and water solutions of cadmium acetate and sodium selenide were used as polar phase. The peculiarities of photoluminescence (PL) and optical absorption spectra of CdTe QDs in the 4.2 K-300 K temperature range were investigated. PL spectrum consist of relatively narrow exciton line with maximum at 2.1-2.4 eV for QDs synthesized at different content of thioglycolic acid (TGA) and L-cysteine (L-cys). It was shown that the Stokes shift in PL and optical absorption spectra monotonically increases from 170 meV to 200 meV at decreasing of QDs size from 3.1 nm to 1.8 nm that is caused by the increasing of the electron-phonon interaction. The dependence of the Huang-Rhys factor on QDs size was obtained.