In2S3 Nanocolloids with Excitonic Emission:  In2S3 vs CdS Comparative Study of Optical and Structural Characteristics

Stable aqueous colloids of 2−3 nm In2S3 nanocrystals have been prepared by using the classical method of nanoparticle stabilization by low molecular weight thiols. TEM crystal lattice spacing, X-ray diffraction, EDAX data, and electron diffraction indicate that the nanoparticles are predominantly in β-In2S3 form. They exhibit relatively strong excitonic emission at 360−380 nm with a quantum yield of 1.5%. The excitonic radiative lifetime is 350 ns, which indicates that a direct allowed electronic transition is responsible for this emission. The NMR lines of the stabilizer are strongly broadened and shifted as a result of deshielding induced by electron withdrawing by positively charged metal ions. This effect quickly wears off as the carbon chain becomes longer and the separation between the hydrogen atoms of the stabilizer and the semiconductor surface increases. The broadening is attributed to the reduced mobility of the stabilizer in the nanoparticle shell. For CdS nanoparticles of the same size, this effect was found to be substantially stronger than for In2S3. The lower density of metal centers in In2S3 than in CdS, which serve as anchor points for the stabilizer, promotes greater mobility of the stabilizer moieties.