Synthesis and luminescence of CdS quantum dots capped with a silica precursor

A novel synthesis method for efficiently luminescing CdS nanocrystals is reported using (3-mercaptopropyl)-trimethoxysilane (MPS) as a capping agent in THF or MeOH. The synthesis yields particles capped with a precursor for coating the particle with a silica shell and offers control over a wide range of particle sizes (2-) by varying the MPS concentration. The temperature dependence of the luminescence and the luminescence life time was studied and explained in terms of a donor-acceptor recombination process in which both electron and hole are trapped at low temperature. In addition to varying the emission color by controlling the particle size, nanocrystals were doped with Zn or Cu resulting in a blue shift or a red shift of the emission.