New infrared nonlinear optical crystal CsGeBr3:: synthesis, structure and powder second-harmonic generation properties

An innovative infrared nonlinear optical crystal CsGeBr3 was synthesized. Ab initio calculations on CsGeBr3 were also carried out in order to analyse the second-order nonlinear susceptibilities. From its powder x-ray diffraction pattern, this crystal was characterized as a rhombohedral structure with an (R3m, No 160) space group symmetry. The reflection powder second-harmonic generation (PSHG) measurement of CGBr showed that its nonlinear optical efficiency is 1.62 times larger than that of rhombohedral CsGeCl3 and is 9.63 times larger than that of KH2PO4 (KDP), and most important of all that CsGeBr3 is phase-matchable. The rescaled d(eff)((2)) of CGBr was about 2.45 times larger than that of rhombohedral CsGeCl3, and this trend was coincident with the ab initio calculation results. The infrared transparent spectrum of rhombohedral CsGeBr3 was extended to more than 22.5 mu m. The rhombohedral CsGeBr3 shows the potential in the realm of nonlinear optics and can be applied to the infrared region.