Formation of Eu2+ and Eu3+ centers in synthesis of CaF2:Eu luminophores

Abstract

UDC 546.161;535.37:(538.958+538.955) We have studied the effect of CaF 2 :Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu 3+ predominates over Eu 2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu 3+ /Eu 2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the samples, due to changes in the excess fluorine balance. We studied the luminescence, magnetic susceptibility, and EPR of the synthesized samples. We have shown that in a solid solution, europium forms large ordered clusters, determining both the luminescent and the magnetic properties of the material.

Synthesis of Radioluminescent CaF2:Ln Core, Mesoporous Silica Shell Nanoparticles for Use in X-ray Based Theranostics

“…However, in the case of Ln = Eu, the MS shell addition increased the relative intensity of the 5 D 1 → 7 F 2 emission, which is perhaps attributable to a change in coordination environment of surface Ln ions ( Figure S2) [55,56]. The relative emission intensities are known to be informative as to the coordination of the Eu dopant ions within the fluorite crystal structure and the dominance of the 5 D 1 → 7 F 2 transition at 591 nm implies that the dopants are replacing Ca 2+ in the lattice [18,19]. Overall, these findings demonstrated the X-ray activation of lanthanide ion luminescence in the CaF 2 :Ln-MS NPs, and we further assessed the CaF 2 :Tb-MS NPs in cyotoxicology experiments, both in the absence and presence of incident X-radiation.…”

“…The photonic and thermal properties of CaF 2 , such as its large bandgap (12 eV) and low phonon energy, reduces non-radiative energy loss and increases the probability of radiative decay at the dopant site, making CaF 2 an effective host matrix in the visible to UV range. Further, the similar ionic radius of Ca 2+ to various fluorescent lanthanide ions, as well as the high symmetry of the cation sites in the face-centered cubic structure of CaF 2 , makes the inclusion of such dopants straightforward and permits the symmetries of their excited states [18,19]. Additionally, CaF 2 has a density of 3.18 g/cm 3 and a higher average atomic number than most biological tissues, properties that increase the probability of X-ray interactions.…”