Optical Amplification from Single Excitons in Colloidal Quantum Dots

The key to utilizing quantum dots (QDs) as lasing materials is to ensure a population inversion, a state that has proved difficult to achieve. A recent paper has addressed this problem by utilizing type II QDs (see scheme; left: type I, right: type II), whose bandgap structures are staggered such that electrons and holes are separated, to achieve population inversion that is solely based on single-exciton states without any biexciton excitations.