The low-temperature fluorescence of single CdS nanocrystals and of single CdS/HgS/CdS quantum well quantum dots (QDQW’s) where an atomic monolayer of HgS is embedded in a CdS nanocrystal is compared. The fluorescence spectrum of the CdS nanocrystals depends strongly on the laser excitation intensity. At high excitation intensity several fluorescence lines can be detected. The total fluorescence intensity of the CdS particles is fluctuating and can be interrupted by dark periods as long as seconds. The spectral and intensity fluctuations are strongly reduced for the QDQW’s which can be explained by charge carrier localization in the HgS region of the nanocrystals. At lowest excitation intensity the linewidth can be narrowed down to sub meV.

• Received 24 December 1998

DOI:https://doi.org/10.1103/PhysRevB.60.1921