Ag3Ga3SiSe8: a new infrared nonlinear optical material with a chalcopyrite structure

An infrared (IR) nonlinear optical (NLO) material, Ag3Ga3SiSe8, has been synthesized for the first time. It crystallizes in the tetragonal chalcopyrite AgGaSe2 structure type and the substitution of Ga3+ with Si4+ generates an equal amount of vacancies at the Ag+ position. Ag3Ga3SiSe8 is a congruent melting compound with a melting temperature of 784 degrees C. The second-harmonic generation (SHG) effect of Ag3Ga3SiSe8 is similar to that of AgGaSe2, as confirmed by the first-principles studies. Moreover, the diffuse reflectance spectra reveal that the energy band gap of Ag3Ga3SiSe is 2.30 eV, 0.44 eV larger compared with AgGaSe2 (1.86 eV). The birefringence of Ag3Ga3SiSe8 is predicted to be above 0.1 at the wavelength of 1 mu m, significantly larger than that of AgGaSe2 (Delta n similar to 0.02). Our results indicate that Ag3Ga3SiSe8 may possess improved optical properties compared with AgGaSe2 and has a promising application as a good IR NLO material.