Hydrochloric acid-mediated mechanical synthesis of red-emitting all-inorganic zinc halides

Abstract

Metal halides (MHs), specifically CsPbX₃ (where X = Cl and Br), have garnered significant research interest due to excellent optoelectronic properties. However, most of these metal halides exhibit no red emission in the visible region. In this study, Cs₂ZnCl₄ powders in the presence of hydrochloric acid were synthesized through mechanical milling. X-ray diffraction (XRD) analyses revealed no detectable diffraction signals before or after acid treatment, suggesting a uniform crystal structure. The initial Cs₂ZnCl₄ powders displayed intrinsic blue emission centered at 486 nm, with a Photoluminescence Quantum Yield (PLQY) of approximately 5.07%. In contrast, the hydrochloric acid-treated Cs₂ZnCl₄ powder exhibited bright red emission centered at 645 nm, with a PLQY of about 12.78%. The broad emission, characterized by a full width at half maximum (FWHM) of 135 nm, was attributed to self-trapped exciton (STE) emission. X-ray photoelectron spectroscopy (XPS) analysis of Cs₂ZnCl₄ before and after acid treatment suggests that hydrochloric acid introduction may have induced distortions or defects in the coordination environment of Zn²⁺ ions. This provides a valuable route for further investigation into the optical properties of other metal halides.