A rare earth L3-edge EXAFS and L1-edge XANES study of Ce, Nd and Eu phosphate glasses and crystals in the composition range from metaphosphate to ultraphosphate

Rare earth (R) phosphate glasses, (R2O3)x(P2O5)1−x, can be prepared with compositions in the range from ultraphosphate, x=0.17 (RP5O14), to metaphosphate, x=0.25 (RP3O9), and it is important to know whether the R–O coordination changes significantly with composition. In rare earth phosphate crystals, the number of nearest neighbour oxygens changes from eight for ultraphosphate to six for metaphosphate. These R–O correlations are clearly distinguished in L3-edge extended X-ray absorption spectroscopy (EXAFS) of NdP5O14 and EuP3O9 crystals. Samples of Ce (x=0.197 and 0.235), Nd (x=0.187) and Eu (x=0.218) phosphate glasses all show the same EXAFS and L1-edge X-ray absorption near edge structures (XANES) results. The results indicate an R–O coordination with six nearest neighbour oxygens, a similar level of static disorder to that in rare earth phosphate crystals and reduced centrosymmetry. There is no evidence for a change in R–O coordination with changing x.