Synergistic combination of different types of functional motif in Rb(NO3)(SO3NH3) for realizing excellent ultraviolet optical nonlinearity

Abstract

The second harmonic generation (SHG) response, birefringence, and ultraviolet (UV) absorption edge are three crucial parameters of UV nonlinear optical (NLO) crystals. However, striking a balance among these parameters has been a challenging endeavor. The synergistic combination of mixed chromophores is regarded as an effective strategy to achieve this task, leveraging the benefits of both functional motifs. Herein, a novel UV NLO crystal, Rb(NO₃)(SO₃NH₃), was successfully designed by integrating the π-conjugated [NO₃] unit with the non-π-conjugated [SO₃NH₃] unit. As anticipated, the π-conjugated [NO₃] units contribute to a robust SHG effect and birefringence, while the non-π-conjugated [SO₃NH₃] units help in widening the band gap and controlling the birefringence within an optimal range by decoupling the π-conjugated interactions and reducing the system's anisotropy. Consequently, it exhibits a strong SHG response (7 × KDP), moderate birefringence (0.07@546 nm), and a short UV absorption edge (208 nm), marking it as a promising UV NLO crystal.