Modulating the Photoluminescence of Europium through Crystalline Assembly Formation with Gold Nanoclusters and Then Phosphate Ions

We report delayed fluorescence enhancement of europium (Eu3+) ions through complexation with ligand-stabilized gold nanoclusters (Au NCs). The different Eu3+-centric emissions following complexation with Au NCs exhibited selective augmentation in the spectral lines attributed to the 5D0 → 7FJ transitions. The photoluminescence (PL) properties, including delayed Eu emission, from each component could be modulated through further functionalization of phosphate ions (Pi), leading to crystallization. The assembled crystalline structure of europium-containing Au NCs (Eu Au NCs) was corroborated by selected area electron diffraction analyses and high-resolution transmission electron microscopy analyses. On the basis of PL measurements and other experimental evidence, the two different lifetimes arising from the components, prompt emission of Au NCs and delayed emission of Eu3+, were affected in the assembled nanostructure. Such a design offers the possibility of developing an optical system by conjugating molecular NCs and atomic luminescent probes that has potential uses.

High-efficient fabrication of core-shell-shell structured SiO2@GdPO4:Tb@SiO2 nanoparticles with improved luminescence

SiO₂@GdPO₄:Tb@SiO₂ nanoparticles with core-shell-shell structure were successfully synthesized by a cheap silane coupling agent grafting method at room temperature. This method not only homogeneously coated rare-earth phosphate nanoparticles on the surface of silica spheres but also saved the use of rare-earth resources. The obtained nanoparticles consisted of SiO₂ core with a diameter of approximately 210 nm, GdPO₄:Tb intermediate shell with thickness of approximately 7 nm, and SiO₂ outer shell with thickness of approximately 20 nm. This unique core-shell-shell structured nanoparticles exhibited strong luminescence properties compared with GdPO₄:Tb nanoparticles. The core-shell-shell structured nanoparticles can effectively quench the intrinsic fluorescence of bovine serum albumin through a static quenching mode. The as-synthesized nanoparticles show great potential in biological cell imaging and cancer treatment.

Controlled synthesis and luminescence properties of core-shell-shell structured SiO2@AIPA-S-Si-Eu@SiO2 and SiO2@AIPA-S-Si-Eu-phen@SiO2 nanocomposites

Two novel core-shell structured SiO₂@AIPA-S-Si-Eu and SiO₂@AIPA-S-Si-Eu-phen nanocomposites have been synthesized by a bifunctional organic ligands ((HOOC)₂C₆H₃NHCONH(CH₂)₃Si(OCH₂CH₃)₃) (defined as AIPA-S-Si) connected with Eu³⁺ ions and silica via covalent bond. And the corresponding core-shell-shell structured SiO₂@AIPA-S-Si-Eu@SiO₂ and SiO₂@AIPA-S-Si-Eu-phen@SiO₂ nanocomposites with enhanced luminescence have been synthesized by tetraethyl orthosilicate (TEOS) hydrolysis co-deposition method. The composition and micromorphology of the nanocomposites were characterized by means of Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). The as-synthesized core-shell and core-shell-shell structured nanocomposites have excellent luminescence intensity and long lifetime. The nanocomposites show bright red light under ultraviolet lamp. However, the core-shell-shell structured nanocomposites have stronger luminescence intensity than the corresponding core-shell structured nanocomposites. Meanwhile, the core-shell-shell structured nanocomposites still exhibit good luminescence stability in aqueous solution. In addition, a large number of Si-OH on the surface of the core-shell-shell structured nanocomposites can be attached to many biomacromolecules. Therefore, they have potential applications in the fields of biology and luminescence.

Luminescence Studies and Judd-Ofelt Analysis on SiO2@LaPO4:Eu@SiO2 Submicro-spheres with Different Size of Intermediate Shells

The novel submicro-spheres SiO₂@LaPO₄:Eu@SiO₂ with core-shell-shell structures were prepared by connecting the SiO₂ submicro-spheres and the rare earth ions through an organosilane HOOCC₆H₄N(CONH(CH₂)₃Si(OCH₂CH₃)₃ (MABA-Si). The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR). It is found that the intermediate shell of the submicro-spheres was composed by LaPO₄:Eu nanoparticles with the size of about 4, 5-7, or 15-34 nm. A possible formation mechanism for the SiO₂@LaPO₄:Eu@SiO₂ submicro-spheres has been proposed. The dependence of the photoluminescence intensity on the size of the LaPO₄:Eu nanoparticles has been investigated. The intensity ratios of electrical dipole transition ⁵D₀ → ⁷F₂ to magnetic dipole transition ⁵D₀ → ⁷F₁ of Eu³⁺ ions were increased with decreasing the size of LaPO₄:Eu nanoparticles. According to the Judd-Ofelt (J-O) theory, when the size of LaPO₄:Eu nanoparticles was about 4, 5-7 and 15-34 nm, the calculated J-O parameter Ω₂ (optical transition intensity parameter) was 2.30 × 10^-20, 1.80 × 10^-20 and 1.20 × 10^-20, respectively. The increase of Ω₂ indicates that the symmetry of Eu³⁺ in the LaPO₄ lattice was gradually reduced. The photoluminescence intensity of the SiO₂@LaPO₄:Eu@SiO₂ submicro-spheres was unquenched in aqueous solution even after 15 days.

Synthesis and photoluminescence properties of novel core–shell–shell SiO2@CePO4:Tb@SiO2 submicro-spheres

The low-cost preparation of the core–shell–shell SiO₂@CePO₄:Tb@SiO₂ was achieved, and the biocompatibility was improved with the use of SiO₂.