Two Lanthanide Borate Chlorides LnB 4 O 6 (OH) 2 Cl (Ln = La, Ce) with Wide Ultraviolet Transmission Windows and Large Second-Harmonic Generation Responses.

Two borate chlorides LaB4 O6 (OH)2 Cl and CeB4 O6 (OH)2 Cl have been synthesized and characterized. Both of them exhibit structure similar to that of notable KBe2 BO3 F2 and feature two-dimensional [B4 O6 (OH)2 ]∞ layers constructed by [B4 O8 (OH)]2 fundamental building blocks. Thermal analyses, infrared spectroscopy, UV-vis-NIR spectra, and second harmonic generation measurement were performed to investigate their physical properties. The results show that both of them have high decomposition temperatures and large second-harmonic generation responses (2.3 and 2.1 × KH2 PO4 , respectively), and LaB4 O6 (OH)2 Cl possesses a deep-UV cutoff edge below 180 nm and large band gap. Moreover, the first-principle calculations were carried out to clarify the role of the electronic structure in determining the associated optical properties of LaB4 O6 (OH)2 Cl. These results demonstrate that LaB4 O6 (OH)2 Cl can be considered as a candidate for ultraviolet nonlinear optical material.