Laser-induced fluorescence line-narrowing in rare-earth-doped glasses: Spectroscopic variations and their structural implications

Abstract

The techniques of laser-induced fluorescence line-narrowing spectroscopy have been applied to the study of a wide variety of oxide and fluoride glasses, doped with Eu 3+ or Nd 3+. All tetrahedral oxidic network formers are found to yield similar spectra, consistent with a common structural model involving a gradual transition from eightfold to ninefold coordination at the rare earth. Effects of changing the proportion and identity of network modifiers, such as alkali or alkaline earth ions, can be readily seen, but unless large amounts of non-tetrahedral network formers are present (e.g. trigonal boron) the same basic structural model remains applicable. Fluoride-containing glasses show much greater variations. In a fluoroberyllate glass, despite its tetrahedral network formers, an entirely different spectroscopic pattern is found; this pattern is also consistent with ninefold coordination, but in a differrent spatial arrangement. Mixed anion glasses, such as the fluorophosphate, show yet a different pattern of behavior, with some evidence of site segregation in Nd 3+-doped specimens. Unitary glasses (pure BeF 2 or SiO 2, with no cationic network modifiers) show patterns too complex to model. Various aspects of the similarities and differences in these glasses are discussed.