Dual mode luminescence in rare earth (Er3+/Ho3+) doped ZnO nanoparticles fabricated by inclusive co precipitation technique

Dual excitation properties have been introduced in ZnO nanoparticles (~10 nm) through lanthanide (Er 3+ /Ho 3+ ) doping by inclusive co precipitation at room temperature. Monophasic hexagonal ZnO nanoparticles form hierarchical micro flowers as a consequence of lanthanide doping. The Stokes and anti Stokes emissions were investigated under UV (399 nm) and IR (980 nm) excitation. The down-conversion emission under band edge excitation is in the blue region and the up-conversion (UC) emission of lanthanide doped ZnO nanocrystals exhibit strong green and red fluorescence bands for ZnO:Er 3+ and only green band for ZnO:Ho 3+ . Post synthesis annealing further improves luminescence properties in ZnO:Er 3+ that exhibits triple mode excitation of fluorescence under UV as well as IR wavelengths 980 and 1550 nm, also confirmed by confocal fluorescence mapping. The measured dependence of pump power on UC emission suggest that lanthanide doping in ZnO leads to frequency up-conversion emission via two to three photon absorption processes.