Semiconductor nanocrystals (NCs) are nanometer-sized crystalline particles that contain approximately 100 to 10,000 atoms. With the use of chemical syntheses, they can be fabricated with almost atomic precision as nearly spherical nanoparticles (quantum dots) [1,2], elongated nano-sized crystals (quantum rods) [3], or nanostructures of other more complex shapes such as tetrapods [4]. Furthermore, by combining different materials in one nanoparticle, it is possible to produce various types of heterostructures including all-semiconductor hetero-nanoparticles [5–8] or hybrid semiconductor-metal structures [9]. The ability to precisely control the composition, size, and shape of NCs provides great flexibility in engineering their electronic and optical properties by directly manipulating electronic wave functions (wave function engineering).