Intense Visible and Near-Infrared Upconversion Photoluminescence in Colloidal LiYF4:Er3+ Nanocrystals under Excitation at 1490 nm

We report intense upconversion photoluminescence (PL) In colloidal LiYF4:Er(3+)nanocrystals under excitation with telecom-wavelength at 1490 nm. The intensities of two- and three-photon anti-Stokes upconversion PL bands are higher than or comparable to that of the Stokes emission under excitation with low power density in the range 5-120 W/cm(2). The quantum yield of the uptonversion PL was measured to be as high as similar to 1.2 +/- 0.1%, which is almost 4 times higher than the highest upconversion PL quantum yield reported to date for lanthanide-doped nanocrystals In 100 nm sized hexagonal NaYF4:Yb(3+)20%, Er(3+)2% using excitation at similar to 980 nm. A power dependence study revealed that the intensities of all PL bands have linear dependence on the excitation power density, which was explained by saturation effects in the intermediate energy states.