SrZnGeS₄ : A Dual-Waveband Nonlinear Optical Material with a Transparency Spanning UV/Vis and Far-IR Spectral Regions

Non-linear optical chalcogenides with a wide band gap (E_g ) and excellent NLO properties are key materials for highly desirable multiwaveband tunable optical parametric oscillators (OPOs). We exploit the "electronic structure engineer bucket effect" to develop a novel dual-waveband SrZnGeS₄ with an ultrawide transparency window. It exhibits an asymmetric Fdd2 structure that consists of layers formed by corner-sharing [ZnGeS₆ ] dimers. SrZnGeS₄ is transparent from 0.30 to 23.6 μm, spanning the UV-, vis-, mid- and far-IR spectral regions and has the widest E_g (3.63 eV) in the AeM^II M^IV Q₄ family to date. It exhibits phase matching, high SHG intensities (e.g., 11.0×KDP and 17.5×AGS under λ_inc =1450 and 950 nm, respectively), and a very high laser-induced damage threshold (35×AGS). These results not only suggest bright prospects for high-power laser applications but may also enable applications of the multiwaveband OPO system from the UV-visible to far-IR regions.