Prediction of MCO [M = S, (Cl2B)3B] Systems with Giant Optical Birefringence and Nonlinearity in the Deep-Ultraviolet Region.

Deep-ultraviolet (DUV) materials with giant optical birefringence and nonlinearity are scarce, and their discovery is very challenging. In this Communication, we predict that the MCO [M = S, (Cl2B)3B] compounds containing the polar C-O motif, which have been synthesized in the experiments, could be the first material systems to achieve this rare capability. First-principles calculations demonstrate that (Cl2B)3BCO and SCO exhibit the largest second-harmonic-generation effect (∼4.4 pm/V) and the largest birefringence (∼0.6) in all known DUV nonlinear-optical (NLO) crystals. In addition, SCO might be a DUV NLO material for the practical 193.7 nm laser output. Our discovery could enrich the structural chemistry of NLO crystals and advance the development of functional DUV optical materials.