Quantum Dots: From Surface Science of Nanoparticles to Cadmium-free Alternatives

Semiconductor quantum dots (QDs) are a class of low-dimensional nanomaterials, some of which can be obtained by colloidal synthesis methods. Unique phenomena occur when electrons are confined to a few nanometers of space, such as highly monochromatic emission and size-dependent wavelength shifts. Owing to the high ratio of surface atoms to the total number of atoms in QDs, not only the crystalline structure of the core, but also surface control is key to achieving high quality emission from QDs. Techniques such as the “hot injection” method, which can produce monodisperse nanoparticles with high crystallinity, and the “core/shell” structure, in which the core is coated with another wide bandgap semiconductor material to confine photoexcited excitons, have improved the emission properties of QDs to the point where they can be used in commercial displays. Efforts are underway to expand applications further by removing cadmium and incorporating QDs into electroluminescent devices. The emergence of various optical devices using these approaches is anticipated.