Multiple sites for Er3+ in alkali silicate glasses (II). Evidence of four sites for Er3+

The low-temperature absorption spectrum of a series of binary alkali silicate glasses doped with Er³⁺ shows the presence of four different sites for the Er³⁺. The near-octahedral A site reported in Part I of this series is the principal site and is present in all these glasses. The B site appears in the binary lithium and sodium silicate glasses. The binary potassium, rubidium and cesium glasses show the presence of the C and D sites. The C site absorption spectrum is similar to that found by Gruber et al. for Er³⁺ in Er₂O₃. The D site is probably a variation of the B site. Tentative sixfold-coordinated models are suggested for the B and D sites.