Luminescence and density functional theory (DFT) calculation of undoped nitridosilicate phosphors for light-emitting diodes

Undoped nitridosilicates that contain a Si-Si bond, SrSi ₆N ₈ and SrSi ₆N _7.95O _0.05, were successfully synthesized by gas-pressure sintering (GPS). Both newly discovered nitridosilicates SrSi ₆N ₈ and SrSi ₆N _7.95O _0.05 were found to exhibit a blue emission (452 nm) under UV excitation (370 nm). Additionally, SrSi ₆N _7.95O _0.05 emits a red emission (652 nm) under blue excitation (460 nm). Based on density functional theory (DFT) calculations from first principles, the electronic structure of a N-vacancy caused a Si extended system in SrSi ₆N ₈ and SrSi ₆N _7.95O _0.05. This phenomenon is predicted using the calculated 2.75 eV (452 nm) energy gap between the 3p-orbitals and the 4s-orbitals of Si, which is consistent with the main peak associated with the emission band and the O-replacement defect system (SrSi ₆N _7.95O _0.05) from a separation of 1.98 eV (652 nm) for the energy gap between the 3s-orbitals and the 2p-orbitals of O.