Keynote
COLLOIDAL DOUBLE QUANTUM DOTS

When considering the term ‘quantum dot’, usually an isolated quantum emitter comes to mind. The advent of colloidal synthesis, however, now enables us to fabricate pairs of quantum dots with controlled coupling between them, a task which is extremely difficult to realize in other systems. The energy landscape of these double quantum dots is tailored by the choice of material composition and size of both the optically active dots and the barrier layer separating them. Double quantum dots can be tailored to exhibit unique optical properties at the single particle level, including two-color antibunching, controlled rapid fluctuations from an emitting to a nearly ‘dark’ state, and a variety of nonlinear optical phenomena. One of the particularly intriguing applications of colloidal double quantum dots is luminescence upconversion, whereby sequential absorption of two photons can lead to photoexcitation of the lower bandgap dot and then to transfer of this excitation to the higher energy one. In particular, broadband upconversion of infrared radiation to visible light in such nanocrystals will be presented.