Studies of Sol-Gel Evolution and Distribution of Eu 3+ Ions in Glass-Ceramics Containing LaF 3 Nanocrystals Depending on Initial Sols Composition.

In this work, we performed a systematic analysis of the impact of selected chemical reagents used in sol-gel synthesis (i.e., N,N-dimethylformamide) and different catalyst agents (i.e., CH ₃ COOH, HNO ₃ ) on the formation and luminescence of Eu ³⁺ -doped SiO ₂ -LaF ₃ nano-glass-ceramics. Due to the characteristic nature of intra-configurational electronic transitions of Eu ³⁺ ions within the 4f ⁶ manifold ( ⁵ D ₀ → ⁷ F _J , J = 0-4), they are frequently used as a spectral probe. Thus, the changes in the photoluminescence profile of Eu ³⁺ ions could identify the general tendency of rare earth materials to segregate inside low-phonon energy fluoride nanocrystals, which allows us to assess their application potential in optoelectronics. Fabricated sol-gel materials, from sols to gels and xerogels to nano-glass-ceramics, were examined using several experimental techniques: X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR), and luminescence measurements. It was found that the distribution of Eu ³⁺ ions between the amorphous silicate sol-gel host and LaF ₃ nanocrystals is strictly dependent on the initial composition of the obtained sols, and the lack of N,N-dimethylformamide significantly promotes the segregation of Eu ³⁺ ions inside LaF ₃ nanocrystals. As a result, we detected long-lived luminescence from the ⁵ D ₀ excited state equal to 6.21 ms, which predisposes the obtained glass-ceramic material for use as an optical element in reddish-orange emitting devices.