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.