Nonlinear optical (NLO) material is one of the important parts of solid-state lasers. It is largely used in laser frequency conversion, optical parameter oscillators, other optical and photonic devices.
Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coeﬃcient, moderate birefringence, chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. For example, β-BaB2O4, LiB3O5 and CsLiB6O10 are successful example of NLO material. Recently, metal phosphates have attracted considerable interests for designing new DUV NLO materials.
A research group led by Prof. PAN Shilie at Xinjiang Technical Institute of Physics & Chemistry (XTIPC) of the Chinese Academy of Sciences developed three new NLO crystals APb2(PO3)5 (A = K, Rb and Cs).
The three compounds are isostructural and belong to the non-centrosymmetric space group of Pn (No. 7). The structures of APb2(PO3)5 (A = K, Rb and Cs) exhibit a 3D network which consists of the PbOn (n = 6, 8), KO7/RbO8/CsO10 and PO4 units.
Researchers found UV-vis-NIR transmittance spectrum result shows that KPb2(PO3)5 has a short deep-UV cutoﬀ edge of 177 nm. It is the shortest UV cut-oﬀ edge among Pb-containing NLO crystals.
Second harmonic generation (SHG) result indicate that KPb2(PO3)5 and RbPb2(PO3)5 are display moderate powder SHG intensities (0.5 × KDP and 0.3× KDP, respectively) in type I phase matching behaviors. Compared with RbBa2(PO3)5, KPb2(PO3)5 has a noticeable enhancement in birefringence (experimental value of 0.03 at 589.3 nm).
To better understand the blue-shift mechanism and enhancement of birefringence in KPb2(PO3)4, researchers employed the theoretical calculations by density functional theory.
As a result, there is almost no hybridization between Pb-6p and O-2p orbitals at the top of valence bands, and therefore, the stereochemistry activity of the lead atom in KPb2(PO3)5 is weak according to the stereochemistry activity mechanism, which causes a blue-shift of the band gap in KPb2(PO3)5.
This work was supported by the National Natural Science Foundation of China.
Figure1：The DUV transmittance spectrum and the photograph of the KPb2(PO3)5 crystal plate. (b) NLO properties of KPb2(PO3)5 and RbPb2(PO3)5 with commercial KDP as a reference(Image by XTIPC)
Figure 2:The front cover of the article(Image by XTIPC)
52 Sanlihe Rd., Beijing,