EXAFS analyses on local structure of gallium in amorphous selenide optical materials doped with rare earths

Ga K-edge EXAFS spectra have been analyzed to elucidate the local coordination structure of Ga in two representative selenide Ge-As-Se and Ge-Sb-Se glasses all doped with Pr. Gallium turned out to be coordinated with 4 Se atoms in its first neighboring shell. This implies that Ga does not follow the 8-N rule associated with the short-range order structures of typical covalent glasses, further indicating there being more ionic-bond nature in the Ga-Se bonds compared to other heteropolar chemical bonds in the selenide glasses. This is decisive for the Pr3+ ions to be incorporated in the selenide glasses. In this case, the GaSe4 units can be electrically neutralized by the doped Pr3+ ions that act as a charge compensator. As such, inside the selenide glasses, distributions of Pr3+ ions and the Ga tetrahedral units are closely correlated. Spectroscopic properties of rare earths embedded in these Ga-containing selenide glasses thus can be explained in connection with the proposed role of Ga.