Crystal, electronic structures and photoluminescence properties of rare-earth doped LiSi 2N 3

Abstract

The crystal and electronic structures, and luminescence properties of Eu 2+, Ce 3+ and Tb 3+ activated LiSi 2N 3 are reported. LiSi 2N 3 is an insulator with an indirect band gap of about 5.0 eV (experimental value ∼6.4 eV) and the Li 2 s, 2 p 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 Eu 2+ is significantly higher than Ce 3+ and Tb 3+ in LiSi 2N 3 which may be strongly related to the valence difference between Li + and rare-earth ions. LiSi 2N 3:Eu 2+ shows yellow emission at about 580 nm due to the 4 f 65 d 1→4 f 7 transition of Eu 2+. Double substitution is found to be the effective ways to improve the luminescence efficiency of LiSi 2N 3:Eu 2+, 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. LiSi 2N 3:Ce 3+ emits blue light at about 450 nm arising from the 5 d 1→4 f 15 d 0 transition of Ce 3+ upon excitation at 320 nm. LiSi 2N 3:Tb 3+ gives strong green line emission with a maximum peak at about 542 nm attributed to the 5D 4→ 7F J ( J=3–6) transition of Tb 3+, which is caused by highly efficient energy transfer from the LiSi 2N 3 host to the Tb 3+ ions.