The synthetic procedure, the characterization, and some photophysical properties of a quantum dot quantum well (QDQW) system are described in detail. The novel structures prepared via wet chemical methods consist of a core of size-quantized CdS and a well of 1-3 monolayers of HgS capped by 1-5 monolayers of CdS acting as the outermost shell. Additionally, theoretical calculations based on the effective mass approximation appropriate to describe the 1s-1s electronic transition of the composite particles are presented.