Paramagnetism and improved upconversion luminescence properties of NaYF 4:Yb,Er/NaGdF 4 nanocomposites synthesized by a boiling water seed-mediated route

• Published in: Frontiers of materials science 2016, Vol.10 (1), p.38-44
• Main Authors: YANG, Chao-Qing, LI, Ao-Ju, GUO, Wei, TIAN, Peng-Hua, YU, Xiao-Long, LIU, Zhong-Xin, CAO, Yang, SUN, Zhong-Liang
• Format: Article
• Language: English
• Subjects: boiling water; fluorescence imaging; nanoparticle; paramagnetism; upconversion
• ISSN: 2095-025X; 2095-0268
• DOI: 10.1007/s11706-016-0318-z

In a route boiling water served as reaction medium, a stoichiometric amount of rare-earth compound and fluoride are put into this system to form α-NaYF 4:Yb,Er nuclei. Then prepared sample is heated at elevated temperature to improve the fluorescence intensity, and next a NaGdF 4 shell grows on the surface of NaYF 4 nuclei. NaYF 4:Yb,Er/NaGdF 4 core--shell structured upconversion nanoparticles (CSUCNPs) have been successfully synthesized by above route. The use of boiling water decreases the cubic-to-hexagonal phase transition temperature of NaYF 4:Yb,Er to 350°C and increases its upconversion (UC) luminescence intensity. A heterogeneous NaGdF 4 epitaxially growing on the surface of Ln 3+-doped NaYF 4 not only improves UC luminescence, but also creates a paramagnetic shell, which can be used as contrast agents in magnetic resonance imaging (MRI). The solution of CSUCNPs shows bright green UC fluorescence under the excitation at 980 nm in a power density only about 50 mW·cm −2. A broad spectrum with a dominant resonance at g of about 2 is observed by the electron paramagnetic resonance (EPR) spectrum of CSUCNPs. Above properties suggest that the obtained CSUCNPs could be potential candidates for dual-mode optical/magnetic bioapplications.