Validity of Valence Estimation of Dopants in Glasses using XANES Analysis.

X-ray absorption near edge structure (XANES) measurement is one of the most powerful tools for the evaluation of a cation valence state. XANES measurement is sometimes the only available technique for the evaluation of the valence state of a dopant cation, which often occurs in phosphor materials. The validity of the core excitation process should be examined as a basis for understanding the applicability of this technique. Here, we demonstrate the validity of valence estimation of tin in oxide glasses, using Sn K-edge and L-edge XANES spectra, and compare the results with Sn Mössbauer analysis. The results of Sn K-edge XANES spectra analysis reveal that this approach cannot evaluate the actual valence state. On the contrary, in L-edge absorption whose transition is 2p-d, the change of the white line corresponds to the change of the valence state of tin, which is calculated from the Sn Mössbauer spectra. Among several analytical approaches, valence evaluation using the peak area, such as the absorption edge energy E at the fractions of the edge step or E at the zero of the second derivative, is better. The observed findings suggest that the valence state of a heavy element in amorphous materials should be discussed using several different definitions with error bars, even though L-edge XANES analyses are used.