Characterization and Luminescence Studies of Europium Doped Lanthanum Fluoride Core-Lanthanum Fluoride Shell Nanoparticles.

摘要

Highly crystalline lanthanum fluoride core-shell nanoparticles can be synthesized using a surfactant-controlled method at low temperature (75 °C) under normal atmospheric pressure. A characterization and luminescence study was obtained on three LaF3 core-shell nanoparticles samples with varying shell thicknesses. The core-shell nanoparticle samples have been characterized for identity, crystallinity, and size using Powder X-Ray Diffraction Transmission Electron Microscopy, and Elemental Analysis. The average diameters are 4.2 nm, 4.6 nm, and 5.0 nm for core-single shell np, core-double shell np, and core-triple shell np samples, respectfully. The core-shell nanoparticles are fully-dispersible in water due to citrate-ion stabilization. The surface of the core-shell nanoparticle has been fully investigated for organic content using Elemental Analysis, including the 'citrate footprint' model, Thermal Gravimetric Analysis, Fourier Transform Infrared Spectroscopy measurements. These methods confirm citrate identity with ∼16-23% citrate by mass for all nanoparticles. A crystal, [La(DPA)3]3-, was grown and analyzed using Single Crystal X-Ray Diffraction where the calculated 0.4 nm distance from ligand to metal center was used in the Forster analysis. Nanoparticle samples analyzed with Energy Dispersive X-Ray (EDX) Spectroscopy with TEM, showed Eu(III) ions do not migrate completely out of the nanoparticle. Luminescence studies include the displacement experiment, the Forster experiment (FRET), and the stability experiment. With the formation of an un-doped LaF3 shell around the doped core, sensitization decreases with an increased shell thicknesses, by evidence of the decreasing asymmetry ratio (5D0→7F2 : 5D0→7F1) values and sensitization (S0→S1/ 7F0→ 5L6) values for all samples. Where ligand sensitized luminescence of Eu3+ ions by dipicolinate (DPA) ligands have been achieved by exciting into a strong DPA absorption band at 278 nm. The absorbed energy is transferred from the excited DPA ligands to Eu3+ ions, which subsequently emit 614 nm light. The Forster experiment shows a distance of energy transfer with 50% probability between the ranges of 2-10 A, which is agreeable to literature. Core-shell nanoparticles are stable in aqueous solutions up to a few weeks; and complete leeching of metal ions out of the lanthanum fluoride nanocrystals was not evident.