Reddish-Orange Luminescence from BaF2:Eu3+ Fluoride Nanocrystals Dispersed in Sol-Gel Materials

Abstract

Nanocrystalline transparent BaF2:Eu3+ glass-ceramic materials emitting reddish-orange light were fabricated using a low-temperature sol-gel method. Several experimental techniques were used to verify structural transformation from precursor xerogels to sol-gel glass-ceramic materials containing fluoride nanocrystals. Thermal degradation of xerogels was analyzed by thermogravimetric analysis (TG) and differential scanning calorimetry method (DSC). The presence of BaF2 nanocrystals dispersed in sol-gel materials was confirmed by the X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). In order to detect structural changes in silica network during annealing process, the infrared spectroscopy (IR-ATR) was carried out. In particular, luminescence spectra of Eu3+ and their decays were examined in detail. Some spectroscopic parameters of Eu3+ ions in glass-ceramics containing BaF2 nanocrystals were determined and compared to the values obtained for precursor xerogels. It was observed, that the intensities of two main red and orange emission bands corresponding to the 5D0→7F2 electric-dipole transition (ED) and the 5D0→7F1 magnetic-dipole (MD) transition are changed significantly during transformation from xerogels to nanocrystalline BaF2:Eu3+ glass-ceramic materials. The luminescence decay analysis clearly indicates that the measured lifetime 5D0 (Eu3+) considerably enhanced in nanocrystalline BaF2:Eu3+ glass-ceramic materials compared to precursor xerogels. The evident changes in luminescence spectra and their decays suggest the successful migration of Eu3+ ions from amorphous silica network to low-phonon BaF2 nanocrystals.

Temperature-Dependent Luminescence of Red-Emitting Ba2Y5B5O17: Eu3+ Phosphors with Efficiencies Close to Unity for Near-UV LEDs

“…This originates from the fact that Eu 3+ can occupy four lattice sites with each giving lines at slightly different wavelengths due to the different crystal field generated. This is the opposite to phosphors where only one lattice site is available for Eu 3+ ions and there are very few excitation lines which, in turn, are also very narrow [13,[26][27][28][29]. The absorption strength of the synthesized phosphors increased with increasing Eu 3+ concentration.…”

Structural and Photoluminescence Investigations of Tb3+/Eu3+ Co-Doped Silicate Sol-Gel Glass-Ceramics Containing CaF2 Nanocrystals

“…Therefore, such materials could be successfully predisposed for use in laser technologies [ 38 ], bio-imaging [ 39 ], or to increase the efficiency of solar cells [ 40 ]. Moreover, according to our previous results for sol-gel nano-glass-ceramics containing divalent metals fluorides, MF 2 (M = Ca, Sr, Ba), singly-doped with Eu 3+ ions, the most efficient segregation of Eu 3+ inside fluoride crystal lattice, was reported for the SiO 2 -CaF 2 system [ 41 , 42 , 43 ]. Indeed, a clear correlation was observed between the average decay time of the 5 D 0 state and growing difference in ionic radius of Eu 3+ and each of individual M 2+ cation in the following order: Ca 2+ → Sr 2+ → Ba 2+ (SiO 2 -CaF 2 :Eu 3+ : τ avg = 11.92; SiO 2 -SrF 2 :Eu 3+ : τ avg = 7.77; SiO 2 -BaF 2 :Eu 3+ : τ avg = 4.08 ms).…”

Luminescence of SiO2-BaF2:Tb3+, Eu3+ Nano-Glass-Ceramics Made from Sol–Gel Method at Low Temperature

“…The xerogels singly doped with Tb 3+ and co-activated with Tb 3+ , Eu 3+ ions were prepared via the previously described sol-gel synthesis [22]. The reagents from Sigma-Aldrich (St. Louis, MO, USA) were applied for the fabrication the samples.…”

“…Our previously published work [22] was concerned with sol-gel SiO 2 -BaF 2 nanoglass-ceramic systems doped with europium ions in a trivalent oxidation state. Their structural and optical properties have been studied using various experimental techniques, such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with the energy-dispersive X-ray spectroscopy (EDS), infrared (ATR-IR), and luminescence spectroscopy.…”