Cadmium telluride nanocrystals (NCs) synthesized by wet chemical routes are very promising objects for various applications including opto- and nanoelectronic devices and biological labeling. However, many of their properties which define the applicability of the NCs, such as radiative recombination pathways, degradation processes, etc., are not fully understood yet.
In this contribution, we report on the synthesis and photoluminescence (PL) investigations of CdTe NCs synthesized in aqueous solution and stabilized with thioglycolic acid. The PL spectra were recorded for the temperature range 5 ? 300 K using different lines of an Ar+-laser for excitation.
Room temperature PL spectra of the NCs consisted of an intensive line due to near-edge recombination and a weak low-energy tail connected with the recombination via deep traps. Depending on the synthesis parameters, the maximum position could vary during the solution storage at room temperature in dark. For some samples, freezing of the solution containing NCs resulted in a red-shift of the PL maximum. After that the energy position of the PL line followed the temperature dependence of the CdTe band gap. We suggest that such an unusual behavior is caused by changes in the passivation conditions at solution freezing. Low-temperature PL spectra measured at different excitation energies clearly showed that the main PL line consists of several components. To explain the observed features, a model which accounts for both the near-edge recombination and the recombination via the states created by the cadmium ? thiol and tellurium ? OH complexes at the surface is proposed.