Crystal, electronic structures and photoluminescence properties of rare-earth doped LiSi2N3

The crystal and electronic structures, and luminescence properties of Eu2+, Ce3+ and Tb3+ activated LiSi2N3 are reported. LiSi2N3 is an insulator with an indirect band gap of about 5.0 eV (experimental value ∼6.4 eV) and the Li 2s, 2p states are positioned on the top of the valence band close to the Fermi level and the bottom of the conduction band. The solubility of Eu2+ is significantly higher than Ce3+ and Tb3+ in LiSi2N3 which may be strongly related to the valence difference between Li+ and rare-earth ions. LiSi2N3:Eu2+ shows yellow emission at about 580 nm due to the 4f65d1→4f7 transition of Eu2+. Double substitution is found to be the effective ways to improve the luminescence efficiency of LiSi2N3:Eu2+, especially for the partial replacement of (LiSi)5+ with (CaAl)5+, which gives red emission at 620 nm, showing highly promising applications in white LEDs. LiSi2N3:Ce3+ emits blue light at about 450 nm arising from the 5d1→4f15d0 transition of Ce3+ upon excitation at 320 nm. LiSi2N3:Tb3+ gives strong green line emission with a maximum peak at about 542 nm attributed to the 5D4→7FJ (J=3–6) transition of Tb3+, which is caused by highly efficient energy transfer from the LiSi2N3 host to the Tb3+ ions.