Structural and electronic properties of amorphous bismuth calcium borate from first-principle calculations

We investigatethe electronic and structural properties of two new amorphous materials, Bi 6 Ca 2 O 28 B 12 and Bi 6 Ca 2 O 28 B 11 :Tm, using density functional theory with a short-range description similar to that for crystalline solids and by considering the Tm 4f states as core states. Our results show that the valence band is formed by broadband states with a strong presence of the O − 2p orbital states in both materials. The thulium-doped structure shows an increased band gap, indicating the strong presence of this rare earth in connection with the oxygen. Both materials exhibit a narrow band gap. Calculations related to the electronic transition of the orbitals between the highest occupied valence band and the lowest unoccupied conduction band and the density charge show a significant contribution of bismuth and oxygen in the formation of both materials. Our results present important information that can assist in the investigation of the technological applications of devices with a design focus for solid-state lasers.