Preparation and Characterization of NaYF4:Yb³+/Er³+ Bio-Upconversion Fluorescence Microcrystallines

Microcrystallines of bio-upconversion (UC) phosphor NaYF₄:Yb³⁺/Er³⁺ were prepared by the complex precipitation method and the hydrothermal method in the presence of sodium citrate. The precusor synthesized by the complex precipitation method was annealed at different temperature, and another was hydrothermal treated at different time. The structure, morphology and upconversion fluorescence of the samples were analyzed by XRD, SEM and Fluorospectrophotometer respectively. The results of XRD showed that the pure hexagonal phase could be obtained by the hydrothermal method. The structure of products that prepared by complex precipitation transfer from cubic to hexagonal to cubic with improving of temperature. The SEM showed that the size of samples increase with the rise of temperature , and morphology is different. The efficient of UC luminescence can be detected under excitation at 976 nm. The spectrum shows the 510~570 nm green emission and 650~700nm red emission are all due to the two-photon process.