Significant Variations in the Luminescence of Samarium(II) Doped Strontium and Barium Octaborate as a Function of Excitation Wavelength and Sample Temperature.

The emission features characteristic of divalent samarium formed in samarium-doped barium octaborate (BaB8O13) and strontium borate (Sr2B16O26) have been studied as a function of excitation wavelength and sample temperature. The emission spectra of divalent samarium in both materials exhibit a surprisingly strong temperature dependence. When divalent samarium is doped into BaB8O13, changes in excitation wavelength and sample temperature both result in significant variations in the emission features associated with the material. It is therefore hypothesized that the variation arises primarily from selected excitation of individual samarium sites within the BaB8O13 matrix. The emission features characteristic of divalent samarium in Sr2B16O26, also exhibited significant variation as the sample temperature was lowered, but this variation was irrespective of the excitation wavelength. This appears to indicate dependence solely on competition between de-excitation pathways.

Characterization of Barium Borate Frameworks Using Raman Spectroscopy.

Systematic micro-Raman scattering investigations have been carried out on Sm+2 doped 2(BaO)-n(B2O3) matrices for n = 4, 5, 8, and 2(BaO)-(Na2O)-9(B2O3) using the 364 nm excitation of an Ar+ laser. The Raman results have been compared with the known structures of barium tetraborate, barium pentaborate, barium octaborate, and barium sodium nonaborate. An excellent correlation has been found between the BO4/BO3 composition ratios for each product and intensity ratios of the designated BO4 and BO3 Raman peaks. Furthermore, the Raman frequencies of both BO4 and BO3 groups undergo a systematic blueshift as n increases from four to nine. The shift results from a decrease of the B-O bond lengths for both BO4 and BO3 groups as the samples transition from the tetraborate to nonaborate structures. Linear relations (with negative slopes) have been determined between the measured Raman frequencies and B-O bond lengths in the frameworks.

Luminescence Study of the Samarium(II) Sites in Samarium: Barium Octaborate as Differentiated by Excitation Wavelength and Temperature.

Divalent samarium incorporated in a barium octaborate matrix prepared by firing homogeneous precipitates has been studied with emission spectroscopy. One of the samarium sites associated with this product exhibits an extremely strong temperature dependence upon using an excitation wavelength of 532 nm. This effect allows for specific differentiation between the two major Sm(II) sites associated with this compound. Based on the assignment of the emission features to specific sites, the symmetry of the first samarium environment is thought to be C3 or C3v while that associated with the second site appears to be C2v.

Photoluminescence and visible diffuse-reflection spectroscopic evidence of samarium reduction in air-fired samples of mixed samarium: strontium tetraborate precipitates.

Photoluminescence and visible diffuse-reflection spectroscopies have provided evidence of the reduction of samarium to the divalent state in samarium-doped strontium borate and pure samarium borate samples. The samples were prepared by the air firing of homogeneous precipitates of divalent strontium and trivalent samarium ions from aqueous solutions with saturated sodium tetraborate. The use of this method in the preparation of divalent lanthanide ions has not been reported previously. Reduced samarium was observed in fired tetraborate precipitates prepared with solutions containing 1, 5, 10, 25, 50, 75, and 90 mole percent samarium versus strontium. Divalent samarium also was identified in fired precipitates of trivalent samarium solutions precipitated with tetraborate. Sm(2+) was identified as the primary emitting species in each of the eight compositions. However, diffuse-reflection spectroscopy indicated the presence of trivalent samarium in the studied samples, ranging from minimal for samples prepared with low samarium concentrations to nearly exclusive when pure samarium was studied. Quenching of the characteristic emission associated with the trivalent species is believed to result in the absence of the emission features arising from residual samarium(III) in the products. Although the absence of trivalent samarium emission enhanced the ability of emission spectroscopy to identify small amounts of divalent samarium, indicating that reduction had occurred, it limited the ability of this method to determine the extent of the reduction. Diffuse-reflection spectroscopy's ability to look at both species provided a much better analysis of the extent of samarium reduction.