Synthesis and characterization of high-efficiency nanocrystal up-conversion phosphors: Ytterbium and erbium codoped lanthanum molybdate

Nanocrystal up-conversion phosphors (UCP), ytterbium- and erbium-codoped lanthanum molybdate (La-2(MoO4)(3):Yb,Er), were prepared for the first time for potential uses in bioassays especially in biochip-based analysis. The La-2(MoO4)(3):Yb,Er nanocrystals, with an average diameter of 50 nm, were prepared via a hydrothermal method. After being annealed at 800 degreesC for 5 h, strong emission of these nanocrystals was observed when excited with a 980 nm infrared (IR) laser. Fluorescent intensity of these nanocrystals is much stronger than that of bulk materials. Down-conversion spectrum of the nanocrystal phosphors was also examined. Two-photon excitation mechanism was proposed for the up-conversion process. Factors affecting the up-conversion fluorescent intensity were also studied. The particle-size-dependent phenomenon was first observed for nanocrystal UCP, and the mechanism was discussed.