Significantly improved photoluminescence properties of ZnO thin films by lithium doping

Photoluminescence (PL) properties of ZnO thin films are increasingly important in the applications of display and lighting, therefore enhancing it by doping different elements becomes the focus of researches. To significantly improve the PL ability, lithium-doped ZnO (LZO) thin films were synthesized via sol-gel method in this study. Different from the previous studies on lithium (Li) doping which emphasized electrical properties, the keystone of our study was put on the optics properties overlooked before, and we systematically investigated the photoluminescence mechanism. This study illustrated that defect concentrations of thin films were enhanced significantly after introducing Li, and doping mode mainly showed interstitial site at high doping concentration (such as 16 at.%). In this meantime, photoluminescence of all thin films showed 12 components including a nearband-edge emission at 393 nm and the eleven defect emissions at 407-581 nm, in which Li-related defects may induce a green emission and a yellow emission at 526 nm and at 574 nm respectively. Delightedly and surprisingly, the 16 at.% LZO thin films handed a huge victory in improvement of overall luminous intensity, which was at least six-fold increase compared with un-doped ZnO. This work may reveal further potential for high performance luminescent devices based on ZnO.