Studies of Sol-Gel Evolution and Distribution of Eu³⁺ Ions in Glass–Ceramics Containing LaF₃ Nanocrystals Depending on Initial Sols Composition

• Main Authors: Natalia Pawlik, Barbara Szpikowska-Sroka, Tomasz Goryczka, Wojciech A. Pisarski
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: International Journal of Molecular Sciences
• Subjects: oxyfluoride glass–ceramics; sol-gel method; Eu³⁺ ions; fluoride nanocrystals
• Online Access: https://www.mdpi.com/1422-0067/22/3/996

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., CH₃COOH, HNO₃) on the formation and luminescence of Eu³⁺-doped SiO₂–LaF₃ nano-glass–ceramics. Due to the characteristic nature of intra-configurational electronic transitions of Eu³⁺ ions within the 4f⁶ manifold (⁵D₀ → ⁷F_J, J = 0–4), they are frequently used as a spectral probe. Thus, the changes in the photoluminescence profile of Eu³⁺ 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 Eu³⁺ ions between the amorphous silicate sol-gel host and LaF₃ nanocrystals is strictly dependent on the initial composition of the obtained sols, and the lack of N,N-dimethylformamide significantly promotes the segregation of Eu³⁺ ions inside LaF₃ nanocrystals. As a result, we detected long-lived luminescence from the ⁵D₀ 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.