Influence of Shell Formation on Morphological Structure, Optical and Emission Intensity on Aqueous Dispersible NaYF4:Ce/Tb Nanoparticles

A Room-Temperature Strategy to Synthesize Ce/Tb-Codoped NaYF4 Nanoparticles with a Photoluminescence Quantum Yield Exceeding 50

NaYF4:Ce3+,Tb3+ down-conversion nanoparticles with a photoluminescence quantum yield (PLQY) of 54.8% are synthesized by using a ligand-assisted coprecipitation method in this study. The reaction is completed within 1 min at room temperature, and short-chain hexanoic acid and hexylamine serve as the binary ligands, which enable us to synthesize highly luminescent NaYF4:Ce3+,Tb3+ nanoparticles at room temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the as-prepared nanocrystals. The results reveal that the NaYF4:Ce3+,Tb3+ nanocrystals exhibit excellent dispersion and have a particle size of 2.7 nm. Our NaYF4:Ce3+,Tb3+ nanocrystals possess the advantages of room-temperature preparation, high PLQY, and ultrasmall particle size. These results reveal that the NaYF4:Ce3+,Tb3+ nanocrystals might have a high potential in the applications of lighting, display devices, and bioimaging.

Facile synthesized NaGdF4 :Yb, Er peanut-shaped, highly biocompatible, colloidal upconversion nanospheres

A facile method was used for the synthesis of peanut-shaped very emissive NaGdF₄ :Yb, Er upconversion nanospheres (UCNSs) at lower temperatures with uniform size distribution. Crystallographic structure, phase purity, morphology, thermal robustness, biocompatibility, colloidal stability, surface chemistry, optical properties, and luminesce properties were explored by X-ray diffraction (XRD), Scanning electron microscope (SEM), transmission electron microscope (TEM), zeta potential, Thermogravimetric/thermal differential analysis (TGA/DTA), Fourier transform infrared (FTIR), UV/visible and photoluminescence spectroscopic tools. XRD pattern verified the construction of a single-phase, highly-crystalline NaGdF₄ phase with a hexagonal structure. Peanut-shaped morphology of the sample was obtained from SEM micrographs which were validated from high-resolution TEM images, have an equatorial diameter of 170-200 nm and a length of 220-230 nm, with irregular size, monodispersed, porous structure, and rough surface of the particles. The positive zeta potential value exhibited good biocompatibility along with high colloidal stability as observed from the absorption spectrum. The prepared UCNSs revealed high dispersibility, irregular size peanut-shaped morphology, rough surface, good colloidal stability, and excellent biocompatibility in aqueous media. A hexagonal phase NaGdF₄ doped with Yb, and Er UCNSs revealed the characteristics of highly dominant emissions located at 520-525, 538-550, and 659-668 nm are corresponding to the ² H_11/2 →⁴ I_15/2 , ⁴ S_3/2 →⁴ I_15/2 , and ⁴ F_9/2 →⁴ I_15/2 transition of Er³⁺ ions, respectively, as a result of energy transfer from sensitizer Yb³⁺ ion to emitter Er³⁺ ion.

Er3+-Ions-Doped Multiscale Nanoprobes for Fluorescence Imaging in Cellular and Living Mice

With the development of biotechnology, luminescent nanoprobes for biological disease detection are widely used. However, the further application in clinic is limited by the reduced penetration depth in the tissues and light scattering. In this work, we have synthesized NaYF4:Yb,Er,Ce@SiO2-OAlg nanomaterials, which have both upconversion and near-infrared (NIR) luminescence. The optimized probes were determined to achieve cell imaging by its upconversion (UCL) luminescence and in vivo imaging through collection of NIR fluorescence signals simultaneously. The research is conducive to developing accurate diagnostic techniques based on UCL and NIR fluorescence imaging by a single nanoparticle.

Physiochemical characterization of highly biocompatible, and colloidal LaF3:Yb/Er upconversion nanoparticles

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF₃ NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8-15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission ⁴S_3/2 → ⁴I/_15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications.

Highly Water-Soluble Luminescent Silica-Coated Cerium Fluoride Nanoparticles Synthesis, Characterizations, and In Vitro Evaluation of Possible Cytotoxicity

A coprecipitation process was utilized for the preparation of terbium fluoride nanocrystals by cerium fluoride. Silica was used to modify the surface of these core/shell nanocrystals. The synthesized CeF₃:Tb@LaF₃ and CeF₃:Tb@LaF₃@SiO₂ nanoparticles (NPs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV/vis spectrophotometry, and photoluminescence spectrophotometry. XRD patterns showed resolved reflection planes with broad widths, confirming the nanocrystalline nature of the CeF₃:Tb@LaF₃@SiO₂ NPs. Fourier transform infrared spectra clearly revealed a uniform, smooth silica layer encapsulating the luminescent seed core and confirmed the polycrystalline nature of the CeF₃:Tb@LaF₃@SiO₂ NPs. The TEM result showed an average crystalline size of 18 nm, which illustrated good agreement with the XRD results. The results of photoluminescence spectrophotometry confirmed the doping of terbium ions in the CeF₃ crystal lattice. The cytotoxicity results of the MTT assay showed that CeF₃:Tb@LaF₃@SiO₂ NPs have minimum toxicity with respect to CeF₃:Tb@LaF₃ NPs and the control drug dasatinib on HT-29 and HepG2 cell lines. Moreover, results of inverted microscopy confirmed the nontoxic and biocompatible nature of CeF₃:Tb@LaF₃@SiO₂ NPs. These findings show that CeF₃:Tb@LaF₃@SiO₂ NPs are promising candidates for applications in biomedical science in the future, such as bioimaging, biolabeling, biodetection or bio-probing, labeling of cells and tissue, drug delivery, cancer therapy, and multiplexed analysis.

Mesoporous multi-silica layer-coated Y2O3:Eu core-shell nanoparticles: Synthesis, luminescent properties and cytotoxicity evaluation

Mesoporous multi-layered silica-coated luminescent Y₂O₃:Eu nanoparticles (NPs) were prepared by a urea-based decomposition process, and their surfaces were gradually modified with nanoporous and mesoporous silica layers using modified sol-gel methods. The synthesized luminescent core-shell NPs were characterized thoroughly to investigate their structural, morphological, thermal, optical, photo luminescent properties and their surface chemistry. The morphology of the core NPs were nearly spherical in shape and were nano-sized grains. The observed luminescent efficiency of the mesoporous multi-layered silica-coated luminescent core NPs was gradually reduced because of bond formation between the Y₂O₃:Eu core and the amorphous silica shell via YOSiOH bridges on the surface of the NPs; the bonds suppressed the non-radiative transition pathways. Biocompatibility tests on Human breast cancer cells using the 3‑(4,5‑Dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide and lactate dehydrogenase assays indicated that the core-shell NPs were non-toxic even at high concentrations. The mesoporous SiO₂ layer played a key role in perfecting the solubility, biocompatibility, and non-toxicity of the NPs. The zeta potential, surface chemistry (Fourier transform infrared spectroscopy), and optical absorption spectral analyses revealed the high hydrophilicity of the as-prepared core-shell NPs because of the active surface-functionalized silanol (SiOH) groups, which could potentially offer many exciting opportunities in photonic-based biomedical applications.

Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties

Monoclinic-type tetragonal LaPO₄ :Eu (core) and LaPO₄ :Eu@LaPO₄ (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO₄ and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications.