  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.
