The four dopants (Nd, Gd, Dy, and Er) substitutionally occupy the Li + sites in lithium tetraborate (Li 2 B 4 O 7 : RE) glasses as determined by analysis of the extended X-ray absorption fine structure. The dopants are coordinated by 6-8 oxygen at a distance of 2.3 to 2.5 Å, depending on the rare earth. The inverse relationship between the RE-O coordination distance and rare earth (RE) atomic number is consistent with the expected lanthanide atomic radial contraction with increased atomic number. Through analysis of the X-ray absorption near edge structure, the rare earth dopants adopt the RE 3+ valence state. There are indications of strong rare earth 5d hybridization with the trigonal and tetrahedral formations of BO 3 and BO 4 based on the determination of the rare earth substitutional Li + site occupancy from the X-ray absorption near edge structure data. The local oxygen disorder around the RE 3+ luminescence centers evident in the structural determination of the various glasses, and the hybridization of the RE 3+ dopants with the host may contribute to the asymmetry evident in the luminescence emission spectral lines. The luminescence emission spectra are indeed characteristic of the expected f-to-f transitions; however, there is an observed asymmetry in some emission lines.