ON THE NATURE AND ROLE OF FE3+ IONS IN OXIDE AND FLUORIDE GLASSES

Fe3+ doped oxide and fluoride glasses were investigated by ESR spectro scopy at 4.2 K. For the first time, the resulting complex spectra coul d be completely reproduced starting from a diagonalization of the S = 5/2 spin-hamiltonian, including the appropriate zero-field splitting c omponents D and E, and using distributions for the fourth order spin c oupling parameters. By careful analysis of the differentiated and inte grated experimental and calculated spectra it could be shown, that if only Fe3+ point defects are present in glasses, the main ESR intensity covers the range of g' similar to 4.3. Since all experimental spectra yield remarkable contributions in the range of g' similar to 2 there is evidence for the existence of magnetically interacting clusters in the glasses. Differences between Fe3+ doped oxide and fluoride glasses essentially concern the concentration dependent spectral pattern and the low-temperature spin relaxation behaviour.