Luminescent properties of local atomic order of Er3+ and Yb3+ ions in aluminophosphate glasses

We report on an extended x-ray absorption fine structure (EXAFS) investigation on the local atomic order around rare earth (RE) ions in Er+Yb doped aluminophosphate glasses. Samples were obtained from the melt and the RE concentration ranged from 0.5 to 5 wt. %. EXAFS data were analyzed within the multiple scattering formalism providing a detailed description of the atomic neighborhood in the first two shells. In particular, each RE in was found to be surrounded by similar to7 PO4 tetrahedra linked by corner O atoms. For RE concentrations below and above the luminescence "quenching" value, no detectable variations are reported leading us to exclude the formation of RE clusters within the sensitivity of the technique. From the analysis of the edge region a description of the density of free 5d states (linked to the radiative emission probability) is also obtained, which again shows no difference at the various RE concentrations.