Visible upconversion luminescence of Tb3+ ions in Y2O3 nanoparticles induced by a near-infrared femtosecond laser

Y2O3:Tb3+ nanoparticles were synthesized using Pechini-type sol–gel method, and characterized by TEM, XRD, and Raman spectra. Their spectroscopic properties are investigated using optical absorption, spectral- and time-resolved upconversion emission spectra. The dependence of Tb3+ emission intensity on pump power density reveals that it is a three-photon excitation process. These results above indicate that upconversion excitation practically originates from the parity-allowed 4f–5d transition via a three-photon simultaneous absorption of Tb3+ ions. The upconversion luminescence intensities of Y2O3:Tb3+ nanoparticles decrease with Tb3+ doping concentrations in the range of 1∼4 mol%. The measured average lifetimes of the 5D4 level of Tb3+ ions also decrease with increasing Tb3+ concentrations at room temperature.