Ln3GaS6 (Ln = Dy, Y): new infrared nonlinear optical materials with high laser induced damage thresholds

Two new ternary rare earth chalcogenides, Dy3GaS6 (1) and Y3GaS6 (2), are reported here. They both crystallize in the orthorhombic space group Cmc2(1) (no. 36). Both are synthesized in pure phase and show phase-matchable second harmonic generation (SHG) of about 0.2 and 0.5 times, respectively for 1 and 2, as strong as that of KTiOPO4 (KTP) based on the powder SHG measurement at the wavelength of 1910 nm. They possess high powder laser induced damage thresholds (LIDTs), respectively, about 14 and 18 times that of AgGaS2 (AGS) based on the powder LIDT measurements under 1064 nm laser irradiation. They both exhibit wide transparency in the IR region (2.5-25 mu m). It is believed that the title compounds are new candidates for nonlinear optical (NLO) materials in the IR region. To gain further insights into the NLO and LIDT properties of 1 and 2, the calculations of second-order NLO susceptibility and lattice energy density (LED) were also performed to explain their SHG efficiencies and high LIDTs.