Design of Experiments and Theoretical Investigation for Photoluminescence Optimization of Copper Aluminum Sulfide Nanoparticles through Controlling Crystalline Defects

Abstract

Copper aluminum sulfide has been explored as an interesting low-toxicity material for application in optoelectronics and biological labeling. Herein, we have applied design of experiments (DOE) and density functional theory simulations (DFT) to investigate the effect of experimental conditions on the optical properties of copper aluminum sulfide nanoparticles synthesized through the heat-up method. The resulting material was characterized by UV–vis-NIR absorption, photoluminescence spectroscopy, X-ray diffractometry (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). XRD and Raman spectroscopy revealed the formation of copper aluminum sulfide alongside byproducts such as covellite, atacamite, paratacamite, and clinoatacamite. DOE revealed the concentration of aluminum precursor as the most important parameter to affect the photoluminescence (PL) intensity. This finding can be correlated to a donor–acceptor pair formed by a copper vacancy and copper substituted by aluminum as the responsible for PL emission. DFT simulations performed for different possible defects reproduced the role of the donor–acceptor pair and provided an insight on their role on PL. The potential application of the nanoparticles for fluorescence biological labeling was confirmed by confocal microscopy assay showing strong fluorescence under excitation at 405, 473, and 559 nm.