Effect of the initial reagents concentration on final crystals size and luminescence properties of PbF₂:Eu³⁺ phosphors

The silica oxyfluoride materials doped with Eu³⁺ ions have been obtained by a facile sol-gel method. The structure of xerogels and powders as well as derivative heat-treated at 350 °C phosphors was examined using scanning transmission electron microscopy (STEM), X-ray diffraction (XRD) measurements as well as FT-IR and Raman spectroscopy. Obtained results clearly indicate the formation of β-PbF₂ micro- and nanocrystalline phase dispersed in amorphous silica matrices during ceramization process. Importantly, it was observed that shape and size modifications of β-PbF₂ crystals are closely related to the quantitative composition of studied samples. Furthermore, the luminescence properties of Eu³⁺ ions have been characterized based on excitation and emission spectra as well as luminescence decay measurements from the ⁵D₀ excited state. The characteristic visible emission in reddish-orange spectral scope corresponding to the 4f⁶-4f⁶ intra-configurational ⁵D₀ → ⁷F_J (0-4) transitions has been observed before and after annealing process. The luminescence intensity R/O-ratios were also calculated. Obtained luminescence spectra and double-exponential character of decay curves measured for powders and glass-ceramic samples after heat-treatment indicated the significant changes in local crystal field around Eu³⁺ ions. In result, conducted luminescence studies and structural characterization indicated the successfully migration of optically active Eu³⁺ ions from amorphous silica framework to low-phonon energy β-PbF₂ micro-/nanocrystal phase after heat-treatment. - Graphical abstract: The β-PbF₂:Eu³⁺ micro- and nanocrystals have been prepared using low-temperature sol-gel method and the long-lived reddish-orange emission from the ⁵D₀ excited state of Eu³⁺ dopant has been registered. - Highlights: • Eu³⁺-doped β-PbF₂ micro- and nanocrystals have been prepared. • Modification in quantitative composition leads to the change in crystal size. • The structure of obtained phosphors was examined. • The luminescence properties of silicate sol-gel materials have been examined.