Cu₄MnGe₂S₇ and Cu₂MnGeS₄: two polar thiogermanates exhibiting second harmonic generation in the infrared and structures derived from hexagonal diamond

Abstract

The synthesis, structure, and physicochemical characterization of two diamond-like semiconductors are reported. Both compounds display second harmonic generation, bandgaps around 2 eV and wide windows of optical transparency in the infrared.

Crystal structure, electronic structure, and optical properties of the novel Li4CdGe2S7, a wide-bandgap quaternary sulfide with a polar structure derived from lonsdaleite

“…The cationsulfur bonds containing S4 are the longest in each of their respective tetrahedra. Similar subtle structural distortions have been observed in other I 4 -II-IV 2 -VI 7 compounds, for example, Cu 4 FeGe 2 S 7 , Cu 4 CoGe 2 S 7 , Li 4 CdSn 2 S 7 , Cu 4 Mn-Ge 2 S 7 , and Cu 4 ZnGe 2 Se 7 (Craig et al, 2020;Zhang, Stoyko et al, 2020;Glenn et al, 2021;Sinagra et al, 2021).…”

“…Using two slightly dissimilar r 0 for the Cd-S bond that are provided by two different sources, the two G values calculated for both Li 4 CdGe 2 S 7 and Li 2 CdGeS 4 , 0.08 (or 0.09) and 0.07 (or 0.09), respectively, are well within the range indicative of reasonable structural strain (0.05 < G < 0.2) (Table 7). These values are lower than those calculated for similar compounds reported by our group, for example, Cu 4 ZnGe 2 Se 7 , Cu 2 Mn-GeS 4 , and Cu 4 MnGe 2 S 7 , which range from 0.16 to 0.20 (Sinagra et al, 2021;Glenn et al, 2021). These results, in addition to the excellent refinement statistics of the singlecrystal structure, give us confidence in our structure solution and refinement for the title compound.…”

“…We were not able to estimate the three-photon absorption coefficient as the sample was ungraded; however, the data seem to indicate the case for saturable absorption, a phenomenon that we have also observed for other diamondlike compounds (Zhang, Stoyko et al, 2020;Glenn et al, 2021). For example, Cu 2 MnGeS 4 (Glenn et al, 2021), Li 4 CdSn 2 S 7 (Zhang, Stoyko et al, 2020), and Li 2 CdGeS 4 (Jang et al, 2014) have also been found to exhibit saturable absorption. It should be noted that the LIDT for Li 4 CdGe 2 S 7 is much greater than that of the analogous I 2 -II-IV-VI 4 phase Li 2 CdGeS 4 (Jang et al, 2014), and would likely be even higher when prepared in a phase-pure form.…”

“…Li 4 HgSn 2 Se 7 possesses an even narrower bandgap of 2.10 eV, and exhibits a greater PM SHG response of 3.6 Â AGS at = 2.09 mm (Guo et al, 2019). While Cu 4 ZnGe 2 Se 7 displays a very weak SHG response (Sinagra et al, 2021), Cu 4 MnGe 2 S 7 has a second-order NLO susceptibility, (2) , of 2.33 AE 0.86 pm V À1 , assessed at the static limit (Glenn et al, 2021). Recently, we have demonstrated that Li 4 CdSn 2 S 7 is the best I 4 -II-IV 2 -VI 7 IR-NLO candidate material to date, with an excellent balance of properties, an optical bandgap of 2.59 eV, an exceptional LIDT of 12.5 Â AGS ( = 1.064 mm, = 30 ps), and a (2) value of 35 pm V À1 at the static limit (Zhang, Stoyko et al, 2020).…”

Li2Mg2Si2S6 and Li2Mg2Ge2S6: Two nonlinear optical sulfides featuring a unique, polar trigonal structure incorporating ethane‐like anions

“…Metal thiosilicates and thiogermanates are attractive classes of solid-state materials with a rich structural diversity. In these compounds, various tetrel-sulfur anionic building units can be stabilized, including (TS 4 ) 4À , [1][2][3][4][5][6][7][8][9] (T 2 S 6 ) 4À , [10,11] (T 2 S 6 ) 6À , [12][13][14] (T 2 S 7 ) 6À , [15,16] and (T 4 S 10 ) 4À , [17,18] where T = Si or Ge. The tetrahedral (TS 4 ) 4À unit is the most prevalent of these anions in condensed inorganic phases.…”