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Laser damage threshold (LDT) has been considered as a key index, apart from the nonlinear optical (NLO) effect, to characterize the performance of a mid-infrared NLO material. This paper reports and compares the properties of RbIO3 and RbIO2F2 as potential nonlinear optical (NLO) materials to be used in the mid-IR region. RbIO3 is a known compound, and its powder SHG (second harmonic generation) effect is carefully measured in this work for the first time to be as strong as 20 times that of KDP, and its powders show a high damage threshold (LDT) of 125 MW/cm2. In order to investigate the influence on the properties by partially replacing oxygen with fluorine atoms, the new compound RbIO2F2 is synthesized and characterized. Although it also shows relatively strong powder SHG responses 4 times that of KDP, the LDT value of the powders is improved to 156 MW/cm2. The transparent region and the thermal stability of two compounds are also measured with satisfactory results. The electronic structure and the properties of the materials are also investigated by the theoretical approach. All these indicate that RbIO3 and RbIO2F2 are both promising candidates for NLO materials to be used in the mid-IR region and that partially replacing oxygen with fluorine in the molecule can improve the laser damage threshold of the material.

A new nonlinear optical (NLO) borate crystal K2Al2B2O7 (Potassium Aluminum Borate, KAB) has been discovered. The structure has been established by 4-axis X-ray diffraction methods. The material crystallizes in the trigonal space group P321 with a = 8.5657(9) Å, C = 8.463(2) Å and Z = 3. KAB possesses a space arrangement similar to Sr2Be2B2O7 (SBBO). A KAB crystal with a dimensions of 30×15×1 mm3 was grown using the Top-Seeded Solution Growth (TSSG) method. The optical properties of KAB were measured.

Wide bandgap and strong second-order generation (SHG) effect are two crucial but contradictory conditions for practical nonlinear optical (NLO) materials. Herein, a new NLO crystal Pb2GaF2(SeO3)2Cl (I) containing novel functional (GaO3F3)6– octahedra is designed and synthesized by a rational band engineering strategy with aliovalent substitution. Benefiting from the removal of transition metal cations and the introduction of bridged F anions, I exhibits the widest bandgap among all reported phase-matchable NLO selenites. Meanwhile, a strong SHG response more than 4.5 times of KH2PO4 (KDP) is maintained. The dominate role of the (GaO3F3)6– groups to the enlarged bandgap in I are elucidated by first-principles studies.