ZnO quantum dots with blue emission were synthesized by a sol-gel method. A series of control experiments were conducted to explore the origin of the blue emission. It was found that the blue emission arose from neither the quantum confinement nor intermediate products, and it could be achieved only in the presence of Li+ cations and excessive OH- anions. Moreover, the long decay time of the blue emission suggested a defect-related de-excitation process. On the basis of the experimental and calculation results, possible de-excitation paths for light emission were considered, and the origin of the blue emission was determined to be electron transition from the conduction band to interstitial oxygen defects. Excessive OH- anions were responsible for the formation of interstitial oxygen defects, and Li+ ions could stabilize the defects by substituting for Zn atoms. Besides, Li+ ions could block the growth of ZnO quantum dots, broadened their band gap and caused a blue shift of the blue emission.

On the Origin of Blue Emission from ZnO Quantum Dots Synthesized by a Sol-Gel Route. Han, L.L., Cui, L., Wang, W.H., Wang, J.L., Du, X.W.: Semiconductor Science and Technology, 2012, 27[6], 065020