Borate nonlinear optical (NLO) crystals have attracted considerable attention in laser science and technology due to their high resistance against laser-induced damage and high transparency in the UV region. One of the most important preconditions to obtain NLO crystals with good performances is to explore the constitutive relationship between non-centrosymmetric structures and NLO effects.    

Prof. YANG Zhihua, with her co-workers SU Xin, Prof. PAN Shilie, et al. from Xinjiang Technical Institute of Physics & Chemistry (XTIPC), Chinese Academy of Sciences, employed the first-principles calculations to study the structural and electronic properties of Bi₂ZnOB₂O₆ (BZB) successfully on the basis of the density functional theory (DFT).   

 “We have performed a computational study on the crystal structure, electronic structure, chemical bonding, and optical properties of BZB using DFT calculations with the local density approximation (LDA), the calculated results are essentially consistent with the corresponding experimental results.” Prof. YANG Zhihua introduced.   

 Previous studies by display BZB has a strong second-harmonic generation （SHG） efficiency of about 3~4 times that of KDP (KH₂PO₄) under 1064 nm laser radiation, wide optical transmission range (330-3300nm), and melt congruently. Therefore, for BZB, a further combined experimental and theoretical study would help to comprehend the origin of linear and nonlinear optical effects. The result shows that B-O groups, distorted octahedra of transition metal ions with d¹⁰ ZnO₄ and lone-pairs electronic configuration such as BiO₆ were combined into BZB crystal. Via the real-space atom-cutting method and the analysis of the density of SHG effect shown in Fig. 1, it is suggested that (BiO₆)^9- and (B₂O₅)^4-  groups play important roles in the linear and nonlinear optical properties of BZB. These results can provide a few valuable clues for the rational design of new second order NLO materials based on metal borates in the future. 

The result has been published in The Journal of Physical Chemistry C, 2013, 117 (27):14149–14157.   

This work was supported by the “Western Light Joint Scholar Foundation” Program and the “Hundred Talent Program” of Chinese Academy of Sciences，the National Natural Science Foundation of China, the Recruitment Program of Global Youth Experts ((Thousand  Talent Plan, Xinjiang Special Program).   

 Fig. 1 Density of the SHG effect in (BiO₆)^9- group perspective shadow along z axes of BZB