Upconversion luminescence properties of monodisper

摘要

Monodisperse spherical Y_2O_2S:Yb,Ho nanocrystals with particle size about 50 nm were prepared by a modified homogeneous precipitation method combined with low-temperature sulfurization process. The Y_2O_2S:Yb,Ho nanocrystals exhibit an intense green emission assigned to the Ho~(3+) ions ~5F_4, ~5S_2 → ~4I(15/2) transition under 980 nm infrared pump. The upconversion luminescence brightness of Y_2O_2S:Yb,Ho is 526 Cd/m~2 under 4.63 W/cn~2 pump density, indicating that the as-prepared Y_2O_2S:Yb,Ho nanocrystals can meet the requirement of in vivo imaging. The formation mechanism of monodisperse spherical oxysulfide nanoparticles is also discussed.