Web Release Date: February 5,
Preparation and Characterization of Near-Infrared Luminescent Bifunctional Core/Shell Nanocomposites
and
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, People's Republic of China, and Institute of Nanochemistry, Jinan University, Guangzhou 510632, People's Republic of China
Received: July 31, 2007
In Final Form: December 3, 2007
Abstract:
Bifunctional nanocomposites with superparamagnetic and NIR luminescent properties were synthesized by a layer-by-layer and a modified Stöber method. Fe3O4 nanoparticles as the core were coated with NaYF4:Ln3+ (Ln = Nd, Er, Pr, or Ho) to form the first layer. Then, the second layer was coated with silica to improve the chemical stability and photostability. The X-ray diffraction patterns showed that a cubic spinel structure of Fe3O4 and the coexistence of a cubic and hexagonal structure of NaYF4 were obtained. Energy dispersive X-ray (EDX) spectroscopy analysis confirmed the core/shell structure of Fe3O4@NaYF4:Ln3+. Transmission electron microscopy images revealed that the bifunctional nanocomposites consisted of crystalline Fe3O4@NaYF4:Ln3+ cores and amorphous SiO2 shells, in a spherical shape with a narrow size distribution. Magnetic measurements showed that the obtained bifunctional nanocomposites exhibited superparamagnetic behavior. Emission spectra indicated that the bifunctional nanocomposites possessed a high near-infrared (NIR) luminescent intensity. Moreover, the hexagonal phase NaYF4:Ln3+ showed NIR emission 10 to 15 times stronger than the cubic phase.
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