Shell Quantum Dots: Synthesis and Characterization

The physical and optical properties of semiconductor quantum dot s ( QD s) are interesting for a variety of applications. However, due to their very large surface/ volume ratio, semiconductor QDs can also lose some of their desirable properties due to, for example, corrupted surfaces. Thus, the protection and passivation of the QD surface is of major importance for almost all of their possible applications. In most cases, this passivation is performed through the coating of a given semiconductor material with another material having a larger bulk bandgap than the core substance and a relative position of the bands, such that both charge carriers, the electrons, and the holes are confi ned to the core. This energetic situation is called type I. In contrast, in type II structures, the electrons and holes are separated so that one is located in the core material the other in the shell material. Both systems have been synthesized via various routes in recent years, and will be reviewed in the fi rst part of the chapter. Subsequently, data will be provided relating to spherical semiconductor nanoheterostructures exhibiting more than one shell. The section describing ultraviolet visible (UV Vis) active nanomaterials concludes with a review on nonspherical core – shell systems, namely elongated rod like structures, and a brief outline on the characterization of the aforementioned different nanoheterostructures. The timely consideration of steady developments presently being made in the area of infrared ( IR ) active materials is also addressed. Hence, a brief synopsis of the progress that has been achieved in the fi eld to date is followed by a discussion of the synthesis and characterization of a number of near infrared ( NIR ) nanomaterials is presented. Finally, a more in depth discussion of the resultant type I and type II core – shell NIR materials is undertaken.