A balance in SHG response, band gap and birefringence in a series of rare-earth sulfate-iodate

Second harmonic generation (SHG) response, birefringence, and optical band gap are several critical parameters of nonlinear optical (NLO) crystals. However, due to the mutual influence and constraints among the fundamental properties of NLO crystals, simultaneously optimizing these performance parameters poses a significant challenge. Herein, lanthanide iodates crystallizing in centrosymmetric (CS) space group were selected as parents, by introducing [SO 4 ] group and water molecule to induce symmetry breaking, a series of mixed-anion lanthanide iodate-sulfate hydrates, RE(IO 3 )(SO 4 )(H 2 O) 2 ∙H 2 O (RE = Eu, Gd, Tb, Yb, Y), were obtained. Their structures changed from the CS space group of the parents to non-centrosymmetric (NCS) one ( P 2 1 2 1 2 1 ). These crystals exhibit strong SHG responses (0.79−1.21 × KH 2 PO 4 ), moderate birefringence (0.061−0.109), short UV transmission cutoff edges (∼240 nm), and wide optical bandgaps (4.24−4.32 eV), demonstrating their potential as NLO crystalline materials with excellent comprehensive properties. This work highlights a feasible strategy of introducing [SO 4 ] group and water molecule into CS iodates to construct NCS structures, thereby developing potential high-performance NLO crystal materials.