Layered and Cubic Semiconductors AGaM′Q4 (A<SUP>+</SUP> = K<SUP>+</SUP>, Rb<SUP>+</SUP>, Cs<SUP>+</SUP>, Tl<SUP>+</SUP>; M′<SUP>4+</SUP> = Ge<SUP>4+</SUP>, Sn<SUP>4+</SUP>; Q<SUP>2-</SUP> = S<SUP>2</SUP><SUP>-</SUP>, Se<SUP>2</SUP><SUP>-</SUP>) and High Third-Harmonic Generation

초록

Eighteen new quaternary chalcogenides AGaM'Q(4) (A(+) = K+, Rb+, Cs+, Tl+; M'(4+) = Ge4+, Sn4+; Q(2-) = S2-, Se2-) have been prepared by solid-state syntheses and structurally characterized using single-crystal X-ray diffraction techniques. These new phases crystallize in a variety of layered structure types. The tin analogues also adopt an extended three-dimensional network structure as polymorphs. The polymorphism and phase-stability in these cases were studied by thermal analysis and high-temperature in situ X-ray powder diffraction. All compounds are semiconductors with the colored selenides absorbing light in the infrared-green region (1.8 eV < E-g < 2.3 eV) and the mostly white sulfides absorbing light in the blue-ultraviolet range (2.5 eV < E-g < 3.6 eV). Based on third-harmonic generation (THG) measurements, the third-order nonlinear optical (NLO) susceptibilities chi((3)) of the new and previously reported AGaM'Q 1 compounds were determined. These measurements revealed an apparent correlation between the THG response of the sample and its band gap, rather than the crystal structure type. While low-gap materials possess higher nonlinearity in general, we found that layered orthorhombic RbGaGeS4 exhibits an impressive chi((3)) value (about four times larger than that of AgGaS2) even with a large band gap and shows stability under ambient conditions with no significant irradiation damage.

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