Structural Studies of Fluoroborate Laser Glasses by Solid State NMR and EPR Spectroscopies

The structure of glasses in the systems (100 – <i>x</i>)­B₂O₃–<i>x</i>PbF₂ (<i>x</i> = 30, 40, and 50) and 50B₂O₃–(50 – <i>x</i>)­PbO–<i>x</i>PbF₂ (<i>x</i> = 5, 10, 15, 20, 25, 30, 35, 40, and 45) has been studied by solid state NMR and EPR spectroscopies. On the basis of ¹¹B and ¹⁹F high resolution solid state NMR as well as on ¹¹B/¹⁹F double resonance results, we develop a quantitative structural description on the atomic scale. ¹⁹F NMR results indicate a systematic dependence of the fluoride speciation on PbF₂ content: At low <i>x</i>-values, F^– ions are predominantly found on BO_3/2F^– units, whereas, at higher <i>x</i>-values, fluoride tends to be sequestrated into amorphous domains rich in PbF₂. In addition, both pulsed EPR studies of Yb³⁺ doped glasses and photophysical studies of Eu³⁺ doped samples indicate a mixed fluoride/borate coordination of the rare-earth ions and the absence of nanophase segregation effects