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 degrees 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 beta-PbF2 micro- and nanocrystalline phase dispersed in amorphous silica matrices during ceramization process. Importantly, it was observed that shape and size modifications of beta-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 D-5(0) excited state. The characteristic visible emission in reddish-orange spectral scope corresponding to the 4f(6)-4f(6) intra-configurational D-5(0) -> F-7(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 beta-PbF2 micro-/nanocrystal phase after heat-treatment.