Nanosized complex fluorides based on Eu3+ doped Sr2LnF7 (Ln=La, Gd)

Abstract

A simple co-precipitation approach taking place between Ln3+, Sr2+ cations and F− anions, led to the formation of nanocrystalline Eu3+ doped Sr2LnF7 (Ln=La and Gd) complex fluorides. The reaction was carried out in the presence of polyethylene glycol, PEG 6000 as a surfactant/surface modifier, providing small size and homogeneity of the products. The synthesized compounds were composed of small nanoparticles with an average size of 15 nm. All obtained Eu3+ doped compounds exhibited an intensive red luminescence. In the case of gadolinium based compounds, the energy transfer phenomena could be observed from Gd3+ ions to Eu3+ ions. In order to study the structure and morphology of the synthesized fluorides, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements were performed. Also FT-IR spectra of the products were recorded, revealing the presence of PEG molecules on the nanoparticles surface. A spectrofluorometry technique was applied to examine optical properties of the synthesized nanoparticles. Excitation and emission spectra as well as luminescence decay curves were measured and analysed. The performed analysis revealed a red luminescence, typical for the Eu3+ ion situated in the inorganic, highly symmetric matrix. Concentration quenching phenomena and lifetimes shortening, together with an increasing of the Eu3+ doping level, were observed and discussed. Judd-Ofelt analysis was also performed for all doped samples, in order to support the registered spectroscopic data and examine in details structural and optoelectronic properties of the synthesized nanomaterials.