The Functionality of Tetrahedral Units in Fluoroxoiodates: Fluorine-Modulating effects in Iodates with Lone Pair Electrons
How to achieve a good balance between band gap and nonlinear optical (NLO) coefficient (dij) for new infrared (IR) NLO candidates is still a challenge. Introducing lone pair electrons in numerous NLO materials can enhance the second harmonic generation (SHG) effects and possibly enrich structural diversity, but lead to redshift of cut-off edge. Therefore, a modulation strategy is needed to balance the SHG effects and band gaps. In this work, the discrepancy of SHG responses of typical iodates AIO3 and fluoroxoiodates AIO2F2 (A = Na, K, Rb, Cs) was analyzed. The results show that the introduction of fluorine can modulate the effect of the stereochemical activity of lone pairs in iodates. Because of the different bonding behaviors between I-O and I-F, the fluoroiodates with IO2F2 exhibit the superiority in balancing the band gap and NLO response. Furthermore, by the real-space atomic cutting method, the main contribution to NLO performance in the iodates/fluoroiodates is the anionic groups with the lone pair. This work firstly demonstrates the expanding functionality of fluorooxo-tetrahedral units in influencing the lone pair effect, which can further guide the rational design of new NLO materials with balanced performances.