Strong SHG Response via High Orientation of Tetrahedral Functional Motifs in Polyselenide A2Ge4Se10 (A = Rb, Cs)

Nonlinear optical (NLO) materials with strong second harmonic generation (SHG) responses are technologically and scientifically important for tunable lasers. This work puts forward a new strategy for designing promising infrared nonlinear optical (IR-NLO) materials with strong SHG responses by strengthening both the static and induced contributions via the high orientation of NLO functional motifs. Two new polyselenides Rb2Ge4Se10 and Cs2Ge4Se10 are studied to verify the strategy, they have 2D infinite(2)[Ge4Se10](2-) layers comprising highly oriented distorted GeSe4 tetrahedra. Their large SHG signals (8.0 and 8.5 times that of commercial AgGaS2) can be ascribed to both the static contribution enhancement from the high orientation of the local dipole moment of GeSe4 tetrahedra and the induced contribution enhancement from terminal and SeSe bonded Se atoms. The results confirm the effectiveness of the proposed approaches, shedding light on the exploration of practical IR-NLO materials with maximized performance.