Crystal field and molecular orbital theory of MBm centres in glasses

The spectral phenomena in optical fibres with bismuth-doped aluminosilicate glass core are explicated on the basis of a molecular orbital theory and of a Schroedinger equation solution, taking into account the exchange, spin-orbit and crystal field interactions of s, p and d electrons of M atoms (M signifies Bi, Sb, Pb, Sn, In, Te, etc) with ligand orbits of environmental B atoms (B signifies O, S, Se, etc). Energy level diagrams and selection rules of transitions between molecular orbital states of s and p electrons of MBm molecule permit us to determine the energies of the main spectral transitions of absorption and luminescent spectra and their correspondence with experimental spectra of different types of optical fibres is obtained.