Luminescence from ZAIS quantum dots: radiative or nonradiative

Quantum dots have found applications across the semiconductor and biotechnology industries, improving energy efficiency, color purity, and imaging capability. However, the standard quantum dot relies on a heavy metal architecture, which has undesirable environmental impacts. Thus, alternative material systems are desirable. One strategy is the ZnS-AgInS2 (ZAIS) quantum dot which has a metal dichalcogenide chemical structure. Unlike heavy metal quantum dots, these nanoparticles luminesce even when defects are present, and their emission wavelength is tuned by varying the relative composition. Past works have linked the source of this luminescence to a defect-assisted transition recombination process, but the precise mechanism is still unclear. In this work, we investigate the physics of this defect-assisted transition by systematically varying the concentration of defects through a simple quick-cool thermal annealing process which provides control over the crystalline disorder of the nanoparticle. Using a combination of ultraviolet photoelectron spectroscopy and fluorescence measurements, information about the nature of the defect-assisted transition is obtained. In contrast to previous work, we find that the ZAIS quantum dot luminescence has an electronic-based rather than defect-assisted transition mechanism.