Preparation and photophysical properties of luminescent nanoparticles based on lanthanide doped fluorides (LaF_3:Ce~(3+), Gd~(3+), Eu~(3+)), obtained in the presence of different surfactants

摘要

A series of nanomaterials composed of LaF_3:Ce~(3+) 10%, Gd~(3+) 30%, Eu~(3+) 1 % was synthesized via a facile co-precipitation approach. The reaction between appropriate lanthanide (Ln~(3+)) and fluoride ions resulted in the formation of crystalline, Ln~(3+) doped fluorides and was performed in the presence of a series of organic modifiers, acting as surfactants and anti-agglomeration agents. Modifiers such as polyacrylic acid (PAA), ethylenediaminetetraacetic acid (EDTA), citric acid and oleylamine most significantly influenced the morphology and spectroscopic properties of the products. The product obtained in the presence of PAA was composed of the smallest nanoparticles (ca. 5-6 nm), with narrow size/shape distribution. All fluorides synthesized exhibited intensive, bright red luminescence under UV irradiation (λ_(ex) ≈ 250 nm), because of the presence of Eu~(3+) ions in their structure. The efficient intensity of luminescence was a result of indirect excitation, via energy transfer (ET) phenomena occurring in the system (Ce~(3+) -> Gd~(3+) -> Eu~(3+)). The structure and morphology of the obtained nanomaterials were established by powder X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) measurements. Optical properties of the obtained compounds were studied and discussed on the basis of excitation emission spectra and luminescence decay curves. On the basis of the performed measurements, luminescence quantum yield (absolute and relative) and radiative lifetimes were calculated and analyzed. FT-IR spectroscopy was applied to examine the presence of molecules of the organic modifiers on the nanoparticles surface.