Up-conversion luminescence switching in Er3+-containing ZnO nanoparticles through Li+ co-doping

Er3+ doped ZnO nanoparticles were synthesized via chemical combustion method. Spectroscopic measurements show that Er3+ ion is partially doped into ZnO host and the existence of Li+ benefits Er3+ ions incorporation. The up-conversion (UC) spectra indicated that under excitation at 980 nm Er3+doped nanoparticles emit a strong red UC fluorescent band centered at 660 nm assigned to the transitions of 4F9/2 → 4I15/2 of Er3+ ion. A luminescent switching between the main red UC emission at 660 nm and green one centered at 535 nm and 557 nm assigned to the transitions of 2H11/2/4S3/2 → 4I15/2 was presented through Li+ co-doping. The origin of luminescent switching could be attributed to the modification of local crystal field around Er3+ ions due to the introduction of Li+ ions. Our results indicate that rare-earth-ions-doped ZnO nano-materials will have potential application in multicolor fluorescent labels.