posted on 2024-02-23, 17:20authored byDongdong Chu, Kewang Zhang, Congwei Xie, Keith T. Butler, Zhihua Yang, Shilie Pan
The
d0 transition metal oxides are the most commonly
used nonlinear optical (NLO) materials in the visible light region;
however, their limited band gaps seriously hinder their application
in ultraviolet (UV) and deep-ultraviolet (DUV) regions. Achieving
the double enhancement of band gap and birefringence by regulating
anionic units helps to push their phase-matching (PM) wavelength into
UV/DUV regions. Herein, starting from the famous NLO material LiNbO3, a “dual-anion strategy” is proposed to regulate
the [NbO6–xFx] octahedra, and the predicted Li2Nb2O6–xF2x·(LiF)y (x = 1,
2, 4; y = 0, 2) materials exhibit the dual-property
magnification of wide band gaps (3.82–6.26 eV, 1–3 eV
larger than LiNbO3) and extraordinary birefringence (0.100–0.322,
1–4 times that of LiNbO3), along with a strong second
harmonic generation (SHG) response of 2.6–6.2 × KDP. Remarkably,
Li2NbOF5-I and LiNbOF4-II have extremely
short PM wavelength (λPM = 209 nm) ever reported
for d0 transition metal oxyfluorides. Further analysis
uncovers that the fluorinated modification of band edges and the increase
of octahedral anisotropy in [NbO6−xFx] anionic groups are the main reasons for the enhanced PM ability.