Deep Ultraviolet-Transparent Materials with Strong Second-Harmonic Response

Deep ultraviolet (UV) nonlinear optical (NLO) materials with excellent performances are particularly important in laser technology. However, the conflict between large second-harmonic generation (SHG) responses and wide band gaps makes the rational design and syntheses of deep UV NLO materials remain a great challenge. Herein, we report five new and polar deep UV NLO crystals with enhanced SHG responses, Ba3La4O4(BO3)3X (X = F, Cl, and Br) and Sr5La(BO3)4X (X = Cl and Br), which were synthesized by introducing rare-earth cations for constructing oxyborates and borates. The property measurements show that they exhibit not only short UV cut-off edges (lambda cut-off < 190 nm) but also large phase-matching SHG responses (2.3-6.4 x KDP). Especially for Ba3La4O4(BO3)3Br, its SHG response (6.4 x KDP) is the largest in all the reported BO3-type deep UV borates. Systematic studies reveal that the large SHG responses of these compounds can be attributed to the large electronic populations and non-symmetry localization of the electron density of La-O polyhedra in oxyborates, which will provide some new insights into the origin of enhanced SHG responses beyond the anionic group theory.

Automated summary

Deep ultraviolet (UV) nonlinear optical (NLO) materials with excellent performances are particularly important in laser technology. However, the conflict between large second-harmonic generation (SHG) responses and wide band gaps makes the rational design and syntheses of deep UV NLO materials remain a great challenge. Herein, we report five new and polar deep UV NLO crystals with enhanced SHG responses.