Low-Temperature Photoluminescence Dynamics Reveal the Mechanism of Light Emission by Colloidal CuInS2 Quantum Dots

Copper indium sulfide colloidal quantum dots are in focus of the nanocrystal community as their optical properties make them exciting candidates for applications in bioimaging and biosensing, solar cells, luminescent solar concentrators, and lighting. However, fulfilling this application potential is hampered by poor understanding of the mechanism of light emission by these dots. In this work, we study temperature and magnetic field dependent photoluminescence (PL) dynamics and spin dynamics at cryogenic temperatures. We cast our experimental observations against two prevailing models of PL in CuInS2 quantum dots: an excitonic mechanism and a free-to-bound mechanism, in which a delocalized electron recombines with a hole localized at a copper ion. We unambiguously show that the PL occurs as the result of the free-to-bound mechanism.