The upconversion luminescence of Y2O3:Er,Yb nanoparticles was observed by an optical microscope, and in-situ measurement of the upconversion spectra in a single particle level was performed. The nanoparticles were prepared by laser ablation in liquid. The target material was synthesized by a precipitation method and sintered at 1250 degrees C. The particle size of the prepared nanoparticles was a few hundred nm. In the upconversion spectra, the red luminescence (F-4(9/2) -> I-4(15/2)) of the nanoparticles was stronger than their green luminescence (H-2(11/2)/S-4(3/2) -> I-4(15/2)), while the red luminescence of the target material was weaker than its green luminescence. Because nanoparticles have a large specific surface area, the groups with high phonon energy on the surface accelerate the nonradiative relaxation of the red luminescence process. Fragmentation of target material by laser ablation in liquid led to the increase in the ratio of red to green luminescence.

Keywords: Nanoparticle; upconversion; Y2O3; laser ablation; femtosecond laser