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

摘要

We report intense upconversion photoluminescence (PL) in colloidal LiYF4:Er³⁺ 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 of 5–120 W/cm². The quantum yield of the upconversion PL was measured to be as high as ~1.2±0.1%, which is almost 4 times higher than the highest upconversion PL quantum yield reported up to date for lanthanide-doped nanocrystals in 100 nm sized hexagonal NaYF4:Yb³⁺20%, Er³⁺2% using excitation at ~980 nm. 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.