RESUMEN
Two acentric chalcogenide compounds, K2CdGe3S8 and K2CdGe3Se8, were synthesized via conventional high-temperature solid-state reactions. The crystal structures of K2CdGe3S8 and K2CdGe3Se8 were accurately determined by single-crystal X-ray diffraction and crystallize in the K2FeGe3S8 structure type. K2CdGe3S8 is isostructural to K2FeGe3S8 with superior nonlinear optical properties. For the second harmonic generation (SHG) response, K2CdGe3S8 is 18× K2FeGe3S8 for samples of particle size of 38-55 µm. The superior nonlinear optical properties of K2CdGe3S8 over K2FeGe3S8 are mainly contributed by the chemical characteristics of Cd compared with Fe, which are elucidated by nonlinear optical property measurements, electronic structure calculations, and density functional theory calculations. The [CdS4] tetrahedra within K2CdGe3S8 exhibit a higher degree of distortion and larger volume compared to the [FeS4] tetrahedra in K2FeGe3S8. This study possesses a good platform to investigate how d-block elements contribute to the SHG response. The fully occupied d10-elements are better for SHG susceptibility than d6-elements in this study. K2CdGe3S8 is a good candidate as an infrared nonlinear optical material of high SHG response (2.1× AgGaS2, samples of particle size of 200-250 µm), type-I phase-matching capability, high laser damage threshold (6.2× AgGaS2), and good stability.
RESUMEN
Seven acentric sulfides Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) were grown by a high-temperature salt flux method. The crystal structures of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds were determined by single-crystal X-ray diffraction with the aid of solid-state NMR spectroscopy. The Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds are isostructural and crystallize in the Ba6Ag4Sn4S16 structure type. The Sn-containing compound exhibits high structural similarity to Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) with the presence of an interstitial atomic position partially occupied by Sn atoms. The chemical bonding characteristics of Ba6(Cu2.9Sn0.4)Sn4S16 were understood with electron localization function calculations coupled with crystal orbital Hamilton population calculations. The Ba-S and Cu-S interactions are dominantly ionic, but the Sn-S interactions consist of strong covalent bonding characteristics in Ba6(Cu2.9Sn0.4)Sn4S16. The monovalent Cu atoms, mixed with certain metals with various oxidation states, significantly shift the optical properties of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds. This results in a good balance between the second-harmonic-generation (SHG) response and laser damage threshold (LDT). Ba6(Cu1.9Zn1.1)Sn4S16 possesses a high SHG response and a high LDT of 2.8 × AGS and 3 × AGS, respectively. A density functional theory calculation revealed that CuS4 and SnS4 tetrahedra significantly contribute to the SHG response in Ba6(Cu2Mg)Sn4S16, which also confirmed that CuS4 tetrahedra are crucial for the stability and optical properties of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds revealed by electronic structure analysis.
RESUMEN
Two new quaternary sulfides K2TGe3S8(T = Co, Fe) have been synthesized by a high-temperature solid-state routine and flux growth method. The crystal growth process of K2TGe3S8(T = Co, Fe) was elucidated by in situ powder X-ray diffraction and DSC thermal analysis. The millimeter-sized crystals of K2TGe3S8(T = Co, Fe) were grown. K2CoGe3S8 crystallizes in a new structure type in centrosymmetric space group P1 (no. 2) with unit cell parameters of a = 7.016(1) Å, b= 7.770(1) Å, c = 14.342(1) Å, α = 93.80(1)°, ß = 92.65(1)°, γ = 114.04(1)°. K2FeGe3S8 crystallizes in the K2FeGe3Se8 structure type and the noncentrosymmetric space group P21 (no. 4) with unit cell parameters of a = 7.1089(5)Å, b = 11.8823(8) Å, c = 16.7588(11) Å, ß = 96.604(2)°. There is a high structural similarity between K2CoGe3S8 and K2FeGe3S8. The larger volume coupled with higher degrees of distortion of the [FeS4] tetrahedra compared to the [CoS4] tetrahedra accounts for the structure's shift from centrosymmetric to noncentrosymmetric. The theory simulation confirms that [TS4]T= Co or Fe tetrahedra play a crucial role in controlling the structure and properties of K2TGe3S8(T = Co, Fe). The measured optical bandgaps of K2CoGe3S8 and K2FeGe3S8 are 2.1(1) eV and 2.6(1) eV, respectively. K2FeGe3S8 shows antiferromagnetic ordering at 24 K while no magnetic ordering was detected in K2CoGe3S8. The magnetic measurements also demonstrate the divalent nature of transition metals in K2TGe3S8(T = Co, Fe).
RESUMEN
Pb3P2S8 was structurally characterized three decades ago with a second harmonic generation response. In this work, Pb3P2S8 was revisited to investigate its electronic structure via DFT calculations and optical properties by UV-vis measurements, second harmonic generation tests, laser damage threshold tests, and photocurrent measurements. Pb3P2S8 is constructed by [PbS7] polyhedra and [PS4] tetrahedra, which was supported by crystal orbital Hamilton population (COHP) calculations. The electron localization function (ELF) simulations revealed the dominantly covalent and ionic bonding nature of P-S interactions and Pb-S interactions, respectively, both of which are strongly polarized. Pb3P2S8 is an indirect n-type semiconductor of 1.8 eV and 2.4(1) eV, which are obtained from DFT calculations and UV-vis measurements, respectively. Pb3P2S8 is a non-type-I phase matching material with a good balance of second harmonic generation (SHG) and laser damage threshold (LDT) of 3.5 × AGS and 2.6 × AGS, respectively (SHG based on 38-50 µm particle size sample). Pb3P2S8 exhibits an intriguing photocurrent response of 45 µA cm-2 under light irradiation. Pb3P2S8 is a new multifunctional material combining a nonlinear optical response and photocurrent response.
RESUMEN
Three ternary thiophosphates α-Ba2P2S6, ß-Ba2P2S6, and Pb2P2S6 were synthesized via a high temperature salt flux method or an I2 transport reaction. ß-Ba2P2S6 and Pb2P2S6 were previously structurally characterized without investigating their optical properties. α-Ba2P2S6 was discovered for the first time, and it is isostructural to Pb2P2S6 and crystallizes in the acentric space group Pn (no. 7). ß-Ba2P2S6 crystallizes in the centrosymmetric space group P21/n (no. 14). There is a high structural similarity between α-Ba2P2S6, ß-Ba2P2S6, and Pb2P2S6 including close unit cell parameters and identical [P2S6] motifs. The structural relationships between α-Ba2P2S6 and ß-Ba2P2S6, and ß-Ba2P2S6 and Pb2P2S6 were elucidated by single crystal X-ray diffraction, differential scanning calorimetry (DSC), electronic structure calculations, and nonlinear optical property measurements. There are no phase transitions detected between α-Ba2P2S6 and ß-Ba2P2S6. From centrosymmetric ß-Ba2P2S6 to acentric Pb2P2S6, the chemical characteristics of Pb, such as stereoactive lone pairs, play a key role in the structural difference. Pb2P2S6 is uncovered as a type-I phase-matching material with a moderate second harmonic generation (SHG) response of 1.4 × AgGaS2 and a high laser damage threshold (LDT) of 2.5 × AgGaS2. α-Ba2P2S6 is not a type-I phase-matching material with a moderate second harmonic generation response (1.7 × AgGaS2, a sample of 225 µm particle size) and a high laser damage threshold (5.5 × AgGaS2).
RESUMEN
Three acentric type-I phase-matchable infrared nonlinear optical materials KSbP2S6, KBiP2S6, and K2BaP2S6, showing excellent balance between the second harmonic generation coefficient, bandgap, and laser damage threshold, were synthesized via a high-temperature solid-state method. KSbP2S6 is isostructural to KBiP2S6, which both crystallize in the ß-KSbP2Se6 structure type. K2BaP2S6 was discovered for the first time, which crystallizes in a new structure type. KSbP2S6 and KBiP2S6 exhibit close structural similarity to the parent compound, centrosymmetric Ba2P2S6. The [P2S6] motifs, isotypic to ethane, exist in Ba2P2S6, KSbP2S6, KBiP2S6, and K2BaP2S6. The mixed cations, K/Sb pair, K/Bi pair, and K/Ba pair, play a dual-role of aligning the [P2S6] structure motifs, contributing to a high SHG coefficient, as well as enlarging the bandgap. KSbP2S6, KBiP2S6, and K2BaP2S6 are direct bandgap semiconductors with a bandgap of 2.9(1) eV, 2.3(1) eV and 4.1(1) eV, respectively. KSbP2S6, KBiP2S6, and K2BaP2S6 exhibit a high second harmonic response of 2.2× AgGaS2, 1.8× AgGaS2, and 2.1× AgGaS2, respectively, coupled with a high laser damage threshold of 3× AgGaS2, 3× AgGaS2, and 8× AgGaS2, respectively. The DFT calculations also confirm that the large SHG coefficient mainly originates from [P2S6] anionic motifs.