Date of Award

4-3-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics & Astrophysics

First Advisor

Kanishka Marasinghe

Abstract

The atomic-scale structure of rare-earth doped phosphate glasses with compositions (R2O3)x(P 2O5)1-x where R = Pr & Nd and 0.05 < x< 0.25 and rare earth doped sodium phosphate glasses with compositions (R2O3) x(Na2O)y(P2O 5)1-x-y where R = Nd, Eu and Dy, 0.04 < x< 0.13, and x + y ∼ 0.4 have been studied using the high energy X-ray diffraction technique. Structural features such as inter-atomic distances and coordination numbers and their dependence on the concentration of the rare-earth oxide have been obtained by analyzing pair distribution functions extracted from diffraction data. Emission spectra for rare-earth doped sodium phosphate glasses were also studied. Rare earth phosphate glasses with x< 0.16 were noticeably hygroscopic and had to be handled under controlled atmospheres. None of the rare earth sodium phosphate glasses investigated herein appeared to be hygroscopic. The P-O coordination number and near-neighbor P-O, O-O, P-P, and R-P distances are virtually independent of the R2O3 content. Pr-O coordination number decreases from approximately 8 to 6.0 as the Pr2 O3 content (x) exceeds 0.2. Structure factors and pair distribution functions for (Pr2O3) x(P2O5)1 -x glasses strongly indicate a significant change in rare-earth near neighbor coordination environment as x is increased beyond ∼ 0.20. In the case of (R2O3)x(Na 2O)y(P2O5) 1-x-y glasses, R-O coordination number decreases from approximately 9 to 6 as x increases from ∼ 0.05 to ∼ 0.13. It appears that the structural change induced by rare-earth doping occurs at much smaller rare-earth concentration in rare earth sodium phosphate glasses as compared to in rare-earth phosphate glasses. In contrast, this change occurs at similar [O]/[P] ratios, 2.9–3 approximately, in both families of glasses. This observation suggests that it is the [O]/[P] ratio of the glass and not the rare-earth oxide concentration (x) that primarily drives the change in rare-earth coordination environment. Emission spectra of rare earth phosphate glasses show that their florescence efficiency decreases with increasing rare-earth content even at relatively low concentrations (0.05 < x< 0.25) investigated suggesting that concentration quenching of lasing action may be present even at these concentrations.

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