AAg 3 Ga 8 Se 14 (A = Rb, Cs): second-harmonic generation responses realized through the parallel arrangement of AgSe 4 and GaSe 4 tetrahedrons.

Two new quaternary selenides AAg 3 Ga 8 Se 14 , (A = Rb, 1; Cs, 2) were synthesised via solid-state reaction in sealed silica tubes. Compounds 1 and 2 crystallised in the monoclinic space group Cm (no. 8) and their three-dimensional [Ag 3 Ga 8 Se 14 ] - anionic frameworks were comprised of AgSe 4 and GaSe 4 tetrahedrons. Their UV-Vis-near infrared diffuse reflectance spectra showed that 1 and 2 possessed wide band gaps of 2.17 and 2.10 eV, respectively. Notably, under incident laser irradiation at 1910 nm, compounds 1 and 2 presented moderate second-harmonic generation responses of 0.6 and 0.7 × AgGaS 2 , respectively, with phase-matching behaviours due to the parallel arrangement of nonlinear optical (NLO) functional tetrahedral AgSe 4 and GaSe 4 units. The laser-induced damage thresholds of 1 and 2 were estimated to be 25.4 and 18.0 MW cm -2 , respectively, which were 2.1 and 1.5 times the threshold of AgGaS 2 . This study revealed that the title selenides, which were constructed from tetrahedral units arranged in a parallel array, are promising infrared NLO materials.