Local structure and valences of samarium in SrB4O7:Sm and SrB6O10:Sm prepared in air

The coordination numbers for the samarium atoms and the SmO bond distances in SrB4O7:Sm and SrB6O10:Sm prepared in air were determined by means of Sm-L3 edge EXAFS. The coordination was found to be nine-folded for both these hosts and the bond distance was 2.40–2.42 Å in SrB4O7:Sm and 2.42–2.44 Å in SrB6O10:Sm. For SrB4O7:Sm the coordination number is coincident with that of the strontium atoms suggesting the substitution of the samarium atoms at the strontium sites. The coordination number of the strontium atoms in SrB6O10 was also suggested to be nine assuming the same type of substitution. The valences of samarium were determined from the luminescent spectra. Both divalent and trivalent ions were present in both SrB4O7:Sm and SrB6O10:Sm, while the fraction of Sm2+ was higher in the former than in the latter. This difference has been assigned to the difference in rigidity between the BO networks in these structures.