Considerable improved near-infrared luminescence in ionic-free doped ZnAl2O4 by oxygen defects engineering

Abstract

Recently, the phosphor for near-infrared LED is of importance, and a lot of the researches have been attracted on the synthesis and composition design. However, the large number of researches for near-infrared luminescent materials mainly focus on activator ions doped inorganic materials, including rare earth ions and transition metal ions. Here, an ionic-free doped NIR phosphor of ZnAl2O4 is proposed for NIR LED through oxygen defects engineering. The spinel-structured ZnAl2O4 phosphors with deficiency of zinc were synthesized by high temperature solid state reaction, which were characterized by a series of techniques, including XRD, UV–Vis, XPS, EPR, DFT calculation, PLE/PL spectroscopy, and temperature-dependent PL spectra analysis. The deficiency of zinc results in the appearance of zinc vacancy (VZn) and oxygen vacancy (VO). Most of the oxygen vacancy is VO+, along with a small content of VO++ in ZnAl2O4. Under the excitation of ultraviolet light at 302 nm, the phosphor outputs a broad near-infrared emission band with the maximum at 715 nm. Higher concentration of zinc deficiency leads to stronger near-infrared luminescence, because of the increased oxygen vacancy. The phosphors exhibited a good thermal stability, and they were successfully packaged on the 285-nm UV LED chip, which outputted bright and intense near-infrared light, indicating that the NIR phosphors synthesized in this work have the prospect application in NIR LED.