A facile ligand engineering strategy to achieve ultra-highly efficient afterglow luminescence of ordinary metal salts

Ordinary metal salts have become a promising afterglow material because of the characteristics of wide sources, low cost, and easy availability. However, their extremely weak afterglow efficiency makes them rarely used in practical applications. In this study, we proposed a ligand engineering strategy to greatly enhance the afterglow efficiency of metal salts. Al₂(SO₄)₃, as a typical metal salt, has only a photoluminescence quantum yield (PL QY) as low as 0.1% and an unmeasurable phosphorescent QY. After doping with dual organic ligands, the PL QY of Al₂(SO₄)₃ has increased by nearly 200 times, reaching 19.90%. Meanwhile, the afterglow intensity of Al₂(SO₄)₃ has increased by approximately 20 times, accompanied by a great increase in phosphorescent lifetime from 416.15 to 2870.08 ms (a about 7-time increase). The enhancement mechanism of afterglow efficiency is ascribed to the fact that the excited electrons from the dual ligands can be directly captured by oxygen defects (trap), then transferred to the emitters (Al³⁺ ions), and ultimately achieving efficient afterglow luminescence. This study utilizes ligand engineering strategy to improve the afterglow luminescence efficiency of metal salts, achieving their applications in deep ultraviolet (UV)-excited light emitting devices and visual ethylene glycol recognition. (Figure presented.)