Abstract
Two novel core-shell composites SiO2@PMDA-Si-Tb, SiO2@PMDA-Si-Tb-phen with SiO2 as the core and terbium organic complex as the shell, were successfully synthesized. The terbium ion was coordinated with organic ligand forming terbium organic complex in the shell layer. The bi-functional organosilane ((HOOC)2C6H2(CONH(CH2)3Si(OCH2CH3)3)2 (abbreviated as PMDA-Si) was used as the first ligand and phen as the second ligand. Furthermore, the silica-modified SiO2@PMDA-Si-Tb@SiO2 and SiO2@PMDA-Si-Tb-phen@SiO2 core-shell-shell composites were also synthesized by sol-gel chemical route. An amorphous silica shell was coated around the SiO2@PMDA-Si-Tb and SiO2@PMDA-Si-Tb-phen core-shell composites. The core-shell and core-shell-shell composites both exhibited excellent luminescence in solid state. The luminescence of core-shell-shell composites was stronger than that of core-shell composites. Meanwhile, an improved luminescence stability property for the core-shell-shell composites was found in the aqueous solution. The core-shell-shell composites exhibited bright luminescence, high stability, long lifetime, and good solubility, which may present potential applications in the bio-medical field.
Highlights
In the last decade, core-shell composite materials, which connect different functional components that are integrated into one unit, have attracted increased attention
Two novel spherical core-shell composites SiO2@PMDA-Si-Tb and SiO2@PMDA-Si-Tb-phen were successfully synthesized with organosilane PMDA-Si acting as a “bi-functional molecular bridge”
The TEM and STEM images showed that the terbium organic complex was successfully coated on the surface of SiO2 spheres and the amorphous silica shell was uniformly encapsulated around these as-prepared core-shell composites
Summary
Core-shell composite materials, which connect different functional components that are integrated into one unit, have attracted increased attention. The Si–O–Si chemical bonds are constructed after the hydrolysis process of X group and the hydroxyl of SiO2 surface In such a method, the silane coupling agent acted as a “bi-functional molecular bridge”, connecting SiO2 spheres and rare earth complexes together. Since the thickness of rare earth organic complexes coating layer is nanometer magnitude, it can significantly save the rare earth resources and greatly reduce the production cost [43–46] These core-shell composites can exhibit excellent luminescence in the solid state; they usually presented poor luminescent stability properties under aqueous medium. Photoluminescence measurement showed that the core-shell-shell composites SiO2@PMDA-Si-Tb@SiO2 and SiO2@PMDA-Si-Tb-phen@SiO2 can exhibit good luminescence properties and stability both in solid state and in aqueous solution medium These core-shell-shell composite materials with surface-attached abundant Si–OH molecules are available for conjugation with biomolecules. After continuous stirring for at least 24 h, the final precipitate was separated from the reaction mixture by centrifugation, washed with ethanol, and dried at 50 ◦C
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