Infrared properties of CsGe(BrxCI1-x)3, nonlinear optical rhombohedral semiconductor

Abstract

Innovative infrared nonlinear optical crystals CsGe( BrxCl1-x)(3) were synthesized. From their powder x-ray diffraction patterns, these crystals were characterized as rhombohedral structure with ( R3m, No 160) space group symmetry. The energy gap decreased from about 3.43 to 2.38 eV as the substitutional ratio, x, changed from zero to unity. Moreover, the powder second-harmonic generation ( PSHG) measurement of CsGeBr3 showed that its nonlinear optical efficiency is 9.64 times larger than that of rhombohedral CsGeCl3 and 28.29 times larger than that of KH2PO4 (KDP), and most important of all, that CsGe( BrxCl1-x)(3) is phase matchable. So the optical nonlinearity is approximately inversely proportional to the cube of the energy gap. The infrared transparent spectrum of rhombohedral CsGe( BrxCl1-x)(3) was extended to more than 30 mu m, which shows the potential in the realm of nonlinear optics and can be applied to the infrared region.