Fluoride Containing Guest Species in Alumosilicates: Tetrafluoroborate in the Sodalite Na 8 Al 6 Si 6 O 24 (BF 4 ) 2

In the course of investigations on optical properties resulting from the interaction of fluorides with alumosilicate host materials and rare earth guests, a well defined BF 4 – ion wasfound to be incorporated within the sodalite of composition Na 8 Al 6 Si 6 O 24 (BF 4 ) 2 . The resulting cubic molecular structure, which was determined by Rietveld methods (space group P 4 $\bar{3}$ n , a = 906.91 pm, wRp = 0.045, Rp = 0.027), contains one anion in each sodalite cage and is, contrarily to expectations, thermally stable. NMR spectroscopic investigations indicated a fast rotatory motion of the BF 4 – tetrahedra at room temperature and agreed with the tetrahedral BF 4 – ions found in IR and Raman spectra. Preliminary attempts to obtain a luminescent material by incorporation of Eu 3+ through aqueous ion exchange only yielded low rare earth concentrations, giving rise to characteristic red emission lines at 581 nm ( 5 D 0 → 7 F 1 ) and 615 nm ( 5 D 0 → 7 F 2 ) in a 1:2 intensity ratio. The material unexpectedly exhibited a strong broad band emission at 520 nm after calcination under Ar, which is attributed to the formation of an Eu 2+ species. Further calcination under air partially reestablished the Eu 3+ emission.