Two Lanthanide Borate Chlorides LnB₄O₆(OH)₂Cl (Ln = La, Ce) with Wide Ultraviolet Transmission Windows and Large Second-Harmonic Generation Responses

Abstract

Two borate chlorides LaB4O6(OH)2Cl and CeB4O6(OH)2Cl have been synthesized and characterized. Both of them exhibit structure similar to that of notable KBe2BO3F2 and feature two-dimensional [B4O6(OH)2]∞ layers constructed by [B4O8(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 × KH2PO4, respectively), and LaB4O6(OH)2Cl 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 LaB4O6(OH)2Cl. These results demonstrate that LaB4O6(OH)2Cl can be considered as a candidate for ultraviolet nonlinear optical material.