Glasses containing trivalent rare earths (REs) exhibit unique luminescence and mechanical properties; however, compared to common silicate glass systems containing light-element alkalis and alkaline earths, there is a lack of understanding of their structures. In the 15 lanthanide elements (La through Lu), the seven 4f orbitals are filled sequentially by 14 electrons, and all have 5s 2 5p 6 electron configurations in their outermost shells. Because of this common electron configuration, the chemical properties of each RE element are similar.