Growth, characterization and theoretical analysis of α-SrGeO3 as a candidate mid-IR stimulated Raman scattering crystal†

Abstract

The α-BaGeO₃ crystal is a potential stimulated Raman scattering (SRS) medium for use in generating lasers at wavelengths in the range of 2.1–2.4 μm. However, the growth of a large-sized and high-quality α-BaGeO₃ crystal is still challenging. Here, we turn the attention to its analogue, α-SrGeO₃. The α-SrGeO₃ crystal was grown by the high-temperature solution method under conditions similar to those for growth of α-BaGeO₃. The grown α-SrGeO₃ single crystals have larger sizes (approximately 8 × 12 × 10 mm³) and higher quality than α-BaGeO₃. A strong Raman peak at 813 cm⁻¹ and a wide transparent window from 0.22 to 5.78 μm indicate that the α-SrGeO₃ crystal is a promising SRS crystal working in the 2.1–2.4 μm wavelength range. From density functional theory (DFT) computations, the strongest Raman peak, the ultraviolet cut-off edge and the infrared cut-off edge of α-SrGeO₃ are all related to the [Ge₃O₉]⁶⁻ ring, the basic building unit in both α-SrGeO₃ and α-BaGeO₃, which suggests that the [Ge₃O₉]⁶⁻ ring is a valuable structural group for developing new mid-IR SRS crystals.