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Rear earths doped upconversion materials have prosmising applications in many fields, such as volumetric color imaging, biomedical detection and encoding, photodynamic therapy of human diseases, continous-wave short-wavelength lasers, etc. Unfortunately, upconversion materials currently have several serious spectrocscopic problems. These problems seriously limit their applications in photonics and biomedicine.Based on BaYF5 nanocrystal, we have performed systematic investigations on size and morphology control, upconversion emission spectral design and upconversion emission enhancement. IR-to-visible upconversion fluorescent nanocrystals of tetragonal BaYF5 have been controllably synthesized by the hydrothermal approach. X-ray diffraction (XRD), Transmission electron microscopy (TEM) and up-conversion stable emission were used to study the cystal structure, size, morphology and luminescenee property of the nanopartieles.The size of the BaYF5 nanocrystal could be changed by varying the pH value of the precursor and the ratio of EDTA:Ln3+. Therefore, the nucleation step and the nucleation rate are discussed in detail, based on the above relationship between the size and the chelating ability of the EDTA in the solution. The emission characteristics of the rare-earth ion doped BaYF5 nanocrystals are investigated in detailed, particularly, the four systems of the red, green and blue up-conversion emission properties of the doped BaYF5:Yb3+,Er3+; BaYF5:Yb3+,Ho3+; BaYF5:Yb3+, Tm3+; BaYF5:Nd3+,Yb,Er3+.These results show BaYF5 nanocrystals have a high efficiency energy transfer, and these nanocrystals have ponential application in the area of biological analysis.
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