Lead fluoride β-PbF2 nanocrystals containing Eu3+ and Tb3+ ions embedded in sol-gel materials: Thermal, structural and optical investigations

Nanocrystalline β-PbF2 phase singly-doped with Eu3+ and Tb3+ ions have been successfully synthesized using sol-gel technique and subsequent heat-treatment of xerogels at 350 °C. Thermal behavior and structural properties of obtained materials were studied using thermogravimetric analysis (TG), differential scanning calorimetry (DSC) as well as FT-IR and Raman techniques. XRD results confirmed formation of β-PbF2 nanocrystals embedded in silica amorphous hosts after annealing at 350 °C. Moreover, the photoluminescence properties have been investigated based on excitation and emission spectra as well as decay analysis from the 5D0 (Eu3+) and the 5D4 (Tb3+) excited states. The sharp intraconfigurational 4f6−4f6 and 4f8−4f8 emission transitions assigned as the 5D0→7FJ (J=0-4) of Eu3+ and the 5D4→7FJ (J=6-3) of Tb3+ bands, respectively, were registered. The most prominent bands in studied xerogels and glass-ceramic materials are related to the following electronic transitions: 5D0→7F1 (orange) and 5D0→7F2 (red) (Eu3+) as well as 5D4→7F5 (green) and 5D4→7F6 (blue) (Tb3+). Thus, the R/O (Eu3+) and G/B (Tb3+) luminescence intensity ratios were calculated and analyzed. Luminescence decay kinetic clearly indicated a presence of two different surroundings around Eu3+ and Tb3+ dopants in β-PbF2-based glass-ceramic samples. In such singly-doped with Eu3+ and Tb3+ materials, the longer luminescence lifetimes (Eu3+: τ1(5D0)=0.90 ms, τ2(5D0)=5.15 ms; Tb3+: τ1(5D4)=0.48 ms, τ2(5D4)=4.01 ms) of an appropriate excited states were achieved in comparison to xerogel hosts (Eu3+: τ(5D0)=0.38 ms; Tb3+: τ(5D4)=0.49 ms). The obtained results indicate the incorporation of Eu3+ and Tb3+ ions into nanocrystalline phase during ceramization process.