서강대학교

초록/요약 도움말

The mixed cation compounds Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 crystallize in the polar noncentrosymmetric space group Cc. The AAsQ(2) (A = alkali metals, Q = S, Se) family features one-dimensional (1D) 1/infinity[AQ(2)(-)] chains comprising corner-sharing pyramidal AQ(3) units in which the packing of these chains is dependent on the alkali metals. The parallel 1/infinity[AQ(2)(-)] chains interact via short As center dot center dot center dot Se contacts, which increase in length when the fraction of K atoms is increased. The increase in the As center dot center dot center dot Se interchain distance increases the band gap from 1.75 eV in gamma-NaAsSe2 to 2.01 eV in Na0.35K0.65AsSe2, 2.07 eV in Na0.2K0.8AsSe2, and 2.18 eV in Na0.1K0.9AsS2. The Na1-xKxAsSe2 (x = 0.8, 0.65) compounds melt congruently at approximately 316 degrees C. Wavelength-dependent second harmonic generation (SHG) measurements on powder samples of Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 suggest that Na0.2K0.8AsSe2 and K-Na0.1(0.9AsS2) have the highest SHG response and exhibit significantly higher laser-induced damage thresholds (LIDTs). Theoretical SHG calculations on Na0.5K0.5AsSe2 confirm its SHG response with the highest value of d(33) = 22.5 pm/V (chi((2))(333) = 45.0 pm/V). The effective nonlinearity for a randomly oriented powder is calculated to be d(eff) = 18.9 pm/V (chi((2))(eff) = 37.8 pm/V), which is consistent with the experimentally obtained value of d(eff) = 16.5 pm/V (chi((2))(eff) = 33.0 pm/V). Three-photon absorption is the dominant mechanism for the optical breakdown of the compounds under intense excitation at 1580 nm, with Na0.2K0.8AsSe2 exhibiting the highest stability.