Luminescent Properties of Eu-Doped Lanthanum Oxyfluoride Sol−Gel Thin Films

Abstract

Highly luminescent Eu3+-doped LaOF thin films have been prepared by a sol−gel procedure using La(hfa)3 diglyme (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = bis(2-metoxyethyl)ether) as a single-source precursor for lanthanum and fluorine. Europium doping (Eu/La = 3 and 10 atom %) has been achieved by adding the proper amount of europium acetate hydrate (Eu(CH3CO2)3·xH2O, x ≤ 4) to the precursor solution. After single-layer deposition, the obtained coatings were heat treated in air up to 700 °C. All the samples, under UV irradiation, presented a bright red luminescence clearly visible to the naked eye notwithstanding the low europium content and the limited film thickness (≤50 nm). The microstructure, composition, and morphology of the samples and their interplay with the synthesis conditions were investigated by glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and field emission scanning electron microscopy (FE-SEM). The luminescence properties of Eu3+:LaOF in the energy and time domains are reported and discussed as a function of europium content and synthesis conditions. The observed variations in the light-emitting behavior of Eu3+ ions have been correlated to the structural and compositional characteristics of the host oxyfluoride matrices.