Résumé
High-resolution Al L2,3 -edge x-ray absorption near edge structure (XANES) spectra have been measured in selected materials containing aluminium in 4-, 5- and 6-coordination. A shift of 1.5 eV is observed between the onset of [4] Al and [6] Al L2,3 -edge XANES, in agreement with the magnitude of the shift observed at the Al K-edge. The differences in the position and shape of low-energy components of Al L2,3 -edge XANES spectra provide a unique fingerprint of the geometry of the Al site and of the nature of Al–O chemical bond. The high resolution allows the calculation of electronic parameters such as the spin–orbit coupling and exchange energy using intermediate coupling theory. The electron–hole exchange energy decreases in tetrahedral as compared to octahedral symmetry, in relation with the increased screening of the core hole in the former. Al L2,3 -edge XANES spectra confirm a major structural difference between glassy and crystalline NaAlSi2 O6 , with Al in 4- and 6-coordination, respectively, Al coordination remaining unchanged in NaAl1 −x Fex Si2 O6 glasses, as Fe is substituted for Al.