X-ray absorption spectroscopic studies of the coordination environment of rare earth ions in novel rare earth phosphate glasses

Rare earth (RE) phosphate glasses (RE$_{2}$O$_{3}$-P$_{2}$O$_{5})$ have exciting magnetic and optical properties with numerous potential applications. These properties depend heavily on the atomic structure, especially the rare earth coordination environment. A series of rare earth (namely neodymium, praseodymium, gadolinium, and erbium) phosphate glasses having low rare earth ion concentrations have been studied with rare earth L$_{III}$ edge X-ray absorption spectroscopy (XAS). Rare earth coordination environment appears to undergo an abrupt change when the RE$_{2}$O$_{3}$ concentration exceeds approximately 15 mol{\%}. Implications of this structural change will be discussed and results from XAS technique will be compared with those obtained with X-ray and neutron diffraction techniques.