Spectroscopic Properties of Eu 3+ Ions in Sol–Gel Materials Containing Calcium Fluoride Nanocrystals

In this study, a series of Eu 3+ ‐doped silicate xerogels with modified initial compositions is prepared and heat treated at 350 °C to fabricate glass‐ceramic materials containing CaF 2 nanocrystals. The impact of an N , N ‐dimethylformamide (DMF) additive and a catalyst agent (CH 3 COOH, HNO 3 ) on the sol–gel transformation from liquid sols through silicate gels and xerogels into glass‐ceramics is investigated using infrared spectroscopy. To verify the formation of CaF 2 nanocrystals, X‐ray diffraction (XRD) measurements are performed. The optical behavior of Eu 3+ ions in the prepared sol–gel materials is evaluated based on photoluminescence excitation (PLE) and photoluminescence emission (PL) spectra as well as luminescence decay analysis. The distribution of Eu 3+ ions between the amorphous silicate hosts and CaF 2 nanocrystals in the prepared glass‐ceramic samples is found due to the biexponential character of registered decay curves. In addition, R/O‐ratio (R/O is defined as ratio I(D5 0 ‐F7 2 )/I(D5 0 ‐F7 1 ) analysis is conducted to characterize the efficiency of Eu 3+ ion migration into precipitated CaF 2 nanocrystals. The lack of DMF as well as HNO 3 as a catalyst in the initial composition significantly promotes the incorporation of Eu 3+ ions into CaF 2 nanocrystals, resulting in long‐lived luminescence with an estimated lifetime τ (D5 0 ) = 12.84 ms.