A new class of far-red and near-infrared fluorescent labels based on semiconductor quantum dots

The past decade has seen explosive growth in research focusing on the properties of nanoscale materials. Semiconductor nanocrystals (also referred to as "quantum dots") have been of particular interest due to their size-dependent electronic and optical properties. Recently developed colloidal chemical synthesis strategies have been successful in producing highly crystalline and nearly monodisperse populations of nanocrystals of several compounds from the III-V and II-VI semiconductor families. Using these high-quality nanocrystals, it has been demonstrated that the photoluminescence (PL) emission maximum can span a wide spectral range simply by changing the particle size. As a result, the PL maximum from semiconductor nanocrystals can be tuned almost continuously from the near-ultraviolet well into the near-infrared region by a judicious choice of material and careful control of the particle size. Several other properties that have caused considerable attention to be given to these nanomaterials are: high quantum efficiencies, narrow, symmetric emission profiles, wide optical absorption bands, large molar absorptivities, and compatibility with organic solvents and biological media.; In this thesis, a careful study is presented of the size-tunable and composition-tunable optical properties of InP, CdSe, CdTe and CdSe1-x Tex nanocrystals, with the emphasis on exploring these materials as a new class of highly luminescent far-red and near-infrared fluorescent dyes. Also examined, are methods for tuning the optical properties of the nanocrystals without changing the particle size. Alloyed semiconductor nanocrystals (CdSe1-xTex) with both homogeneous and gradient internal structures have been developed to achieve continuous tuning of the optical properties without changing the particle size. The results from these studies demonstrate that composition and internal structure are two important parameters that can be used to tune the optical and electronic properties of multi-component, alloyed quantum dots. A surprising finding is a nonlinear relationship between the composition and the absorption/emission energies, leading to new properties not obtainable from the parent binary systems. With red-shifted light emission up to 850 nm and quantum yields up to 60%, this new class of alloyed quantum dots opens new possibilities in band gap engineering and in developing near-infrared fluorescent probes for in vivo molecular imaging.