Abstract: The upconversion nanocrystals NaYF₄∶Er³⁺,Yb³⁺ were prepared by solgel method. The intense upconversion emission was observed from the nanocrystals under excitation at 980 nm. Xray diffraction analysis suggests that the nanocrystals were cubic. The nanocrystals were found to be welldispersed spherical particles with an average diameter of 70 nm by transmission electron microscopy. The nanocrystals are favorable for the highly sensitive label used in biological detection. The upconversion fluorescence spectrum was recorded on a fluorescence spectrometer. Upconversion mechanism was explored.

Key words: upconversion, nanocrystals, lanthanidedoping