Rational Design\nof Novel Polar Nonlinear Optical Materials\nin Alkali Metal Rare Earth Iodates

Four new potassium rare earth iodates, namely, acentric\nK<sub>2</sub>Lu(IO<sub>3</sub>)<sub>5</sub> and KM(IO<sub>3</sub>)<sub>4</sub>(HIO<sub>3</sub>)<sub>0.33</sub> (M = Ce/Pr) and centric KLa(IO<sub>3</sub>)<sub>4</sub>, were successfully grown by mild hydrothermal\nreactions. Three of them exhibit polar structures; K<sub>2</sub>Lu(IO<sub>3</sub>)<sub>5</sub>, KCe(IO<sub>3</sub>)<sub>4</sub>(HIO<sub>3</sub>)<sub>0.33</sub>, and KPr(IO<sub>3</sub>)<sub>4</sub>(HIO<sub>3</sub>)<sub>0.33</sub> show second-harmonic generation (SHG) responses\nof 3.0, 1.0, and 0.8 × KDP, respectively. These three iodates\nare phase-matchable for second-harmonic generation. The influence\nof changes in the radius and coordination mode of rare earth ions\non the crystal structure and SHG response has been discussed in detail.\nOur findings suggest that in the alkali metal rare earth iodate, modulating\nthe arrangement of iodate groups by changing the coordination geometry\nof rare earth ions is an effective strategy for designing polar NLO\nmaterials.