Pb2Cd(SeO3)2X2 (X = Cl and Br): two halogenated selenites with phase matchable second harmonic generation†
Two new halogenated selenites, namely, Pb2Cd(SeO3)2X2 (X = Cl and Br), were synthesized via mild hydrothermal reactions. The isomorphic compounds crystallized in a noncentrosymmetric (NCS) and chiral space group. Their three-dimensional (3D) structures were formed by alternating undulated [Pb2(SeO3)X]∞+ cationic layers and flattened [Cd(SeO3)X]∞− anionic layers. Thermal analyses revealed that the compounds can remain stable up to 500 °C. The SHG efficiencies of Pb2Cd(SeO3)2X2 (X = Cl and Br) are much higher than those of commercial KDP (KH2PO4), and they are phase-matchable. UV-vis-NIR diffuse reflectance spectra revealed that the two compounds exhibited wide optical band gaps. The laser damage thresholds of Pb2Cd(SeO3)2X2 (X = Cl and Br) were measured to be about 38.5 and 35.7 times higher than that of AGS (AgGaS2). Their calculated birefringences were large enough to accomplish phase matching in SHG progression. The SHG density analyses disclosed that the lone pair electrons of the SeO3 and PbOnXm units made major contributions to their nonlinear efficiencies.