In2S3 nanocolloids with excitonic emission: In2S3 vs CdS comparative studyof 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 w eight thiols. TEM crystal lattice spacing, X-ray diffraction, EDAX data, an d electron diffraction indicate that the nanoparticles are predominantly in beta -In2S3 form. They exhibit relatively strong excitonic emission at 360 -380 nm with a quantum yield of 1.5%. The excitonic radiative lifetime is 3 50 ns, which indicates that a direct allowed electronic transition is respo nsible for this emission. The NMR lines of the stabilizer are strongly broa dened and shifted as a result of deshielding induced by electron withdrawin g by positively charged metal ions. This effect quickly wears off as the ca rbon chain becomes longer and the separation between the hydrogen atoms of the stabilizer and the semiconductor surface increases. The broadening is a ttributed to the reduced mobility of the stabilizer in the nanoparticle she ll. For US nanoparticles of the same size, this effect was found to be subs tantially stronger than for In2S3. The lower density of metal centers in In 2S3 than in CdS, which serve as anchor points for the stabilizer, promotes greater mobility of the stabilizer moieties.