1. INTRODUCTION

Colloidal semiconductor nanostructures are most interesting because they conveniently associate the flexibility of chemical synthesis along with the predictable optical properties of semiconductor materials. The field of quantum confined semiconductor nanocrystals probably originates back to 1980 with the discoveries of Ekimov1 and Efros.2 Its extension into colloid chemistry was actively pursued in the 80's, largely under the leadership of Brus,3 Henglein,4 and Nozik.5 By 1993, the monodispersity of the materials was greatly improved with the use of high-temperature solvent and organometallic reagents introduced by C. B. Murray et al.6 To date, the absorption edge of colloid quantum dots covers the whole spectrum from the UV to the mid-infrared with II-VI, III-V and IV-VI materials, along with high monodispersity and fluorescence efficiency. A typical example is shown by PbSe nanocrystals in Figure 1. In many groups, the processing of the colloid materials is evolving towards core-shell heterostructures, and more complex shapes. Furthermore, self-assembly and directed assembly of colloids is also being investigated with the hope that new functions may arise from the interactions. The stable and high-quality materials have spawned a number of potential applications such as photovoltaic materials, light-emitting diodes and lasers, electrochromic materials and fluorescent markers for biological microscopy.

Figure 1: Size dependent linear absorption of monodispersed PbSe nanocrystal colloid solutions. The sizes range from 5 to 10 nm diameter. TEM image of an ordered array of PbSe nanocrystals, the line bar is 20 nm.26

Various levels of theoretical modelling, have been developed, from...