A general design strategy is presented for tuning the convergence of direct and indirect bandgaps based on chemical adjustment of the s- and p-orbital character of the conduction band minimum.

Deep ultraviolet (absorption edge <200 nm, band gap >6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic noncentrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (d ij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.