Influence of the cation size on the second harmonic generation response of chiral A(VO2)2(PO4)·3H2O (A = K+, NH4+ and Rb+)†
New insights into the relationships between chirality and nonlinear optical (NLO) properties are of interest for the future design of phases with strong second harmonic generation (SHG) response. The structures of the new A(VO2)2(PO4)·3H2O (A = K+ and Rb+) phases prepared by the hydrothermal method were determined by single crystal X-ray diffraction. The SHG properties of these new chiral materials and the previously reported isostructural NH4(VO2)2(PO4)·3H2O were measured. For an incident wavelength of 1064 nm, the SHG responses at 532 nm of Rb, NH4 and K analogues were, respectively, 2, 6 and 24 times stronger than that of quartz. The NLO properties were shown to increase strongly when the structure slightly contracts.