Coordinated regulation on physiochemical performances activated from mixed anionic ligands in a new series of IR NLO materials was systematically investigated.

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A new family of thiosilicates with balanced performances were verified as a promising research system for the exploration of IR NLO materials.

In this work, Na4SnS4 and Na4SnSe4 compounds were successfully synthesized and their physicochemical performances were systematically investigated by the experimental and theoretical methods. Research results show that they display the...

High-performance infrared nonlinear optical (IR NLO) materials are crucial devices in tunable IR solid-state lasers, and the functional-group cosubstitution strategy was selected to design and explore outstanding IR NLO crystals. For that reason, taking the famous AgGaSe 2 as the template, five new mercury-based IR NLO selenides, Li 2 HgMSe 4 and Na 2 Hg 3 M 2 Se 8 (M = Si, Ge, Sn), were successfully designed and synthesized through concurrently replacing the cation (Ag + ) and GaSe 4 unit with the alkali metal (Li + or Na + ) and anionic groups (HgSe 4 and MSe 4 ) to optimize crystal structures and performances. All of them exhibit extremely strong powder second-harmonic generation (SHG) responses (3.6−6.0 × commercial AgGaS 2 ) with the essential phase-matching behavior. Note that Li 2 HgSnSe 4 exhibits the largest SHG response (6.0 × AgGaS 2 ) among the known Hg-based chalcogenides without disorder structures, and its millimeter-level single-crystals were successfully grown by the Bridgman method. Theoretical analysis further illustrates that the different arrangement modes of HgSe 4 units offer considerable but distinguishing SHG contributions, such as Li 2 HgMSe 4 (53−55%) and Na 2 Hg 3 M 2 Se 8 (19−23%). This research result highlights the practicability of the functional group cosubstitution-oriented design strategy and Hg-based selenides could be viewed as the optimal system for future exploration of large SHG crystals.

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Two triclinic A 2 ZnSi 3 S 8 (A = Rb and Cs) with layered structures were successfully synthesized, and their physicochemical performances including optical bandgap, thermal behavior, and optical anisotropy were investigated. A 2 ZnSi 3 S 8 could be viewed as the first discovered Si-based examples in the known A 2 M II M IV 3 Q 8 family (2−1−3−8 system; A = monovalent alkali metal; M II = divalent transition metal; M IV = group 14 metal; Q = chalcogen). The A 2 M II M IV 3 Q 8 family members crystallize in five different space groups (P1̅ , P2 1 , P2 1 /n, P2 1 2 1 2 1 , and Pa3̅ ), and their structural transformation and optical performances (bandgap, NLO coefficient, and birefringence) were systematically studied based on the first-principles calculation among 13 A 2 M IIB M IV 3 Q 8 (M IIB = Zn, Cd, and Hg) compounds without cubic β-K 2 ZnSn 3 S 8 . Research result shows that the above 13 compounds exhibit the layered structures, but diverse wavelike layers and their optical anisotropy (Δn) undergo an increasing trend range from the triclinic to orthorhombic systems. Moreover, P2 1 2 1 2 1 compounds have very weak NLO effects compared with those of the P2 1 compounds since the polarization directions of anionic groups (M IIB Q 4 and M IV Q 4 ) in P2 1 2 1 2 1 compounds are directing oppositely and almost completely canceled out by the dipole moment calculation, which further indicates that P2 1 compounds exhibiting the relatively strong NLO effect and large optical anisotropy could be expected as potential IR NLO candidates.

Size and composition-dependences of band gap energies are important properties for nanocrystal semiconductors, and have attracted extensive attentions for the last two decades. In this letter, a simple method of band gap prediction for nanocrystal alloys is developed. The band gaps of II–VI semiconductor homogeneous alloys with zinc blende and wurtzite structure, such as zb-(ZnS)x(CdS)1−x, zb-(CdS)x(CdSe)1−x, zb-(ZnSe)x(CdSe)1−x, w-(ZnS)x(CdS)1−x, w-(ZnSe)x(CdSe)1−x, and w-(CdSe)x(CdTe)1−x nanocrystal alloys, are calculated. The calculated results are in good agreement with the available experimental data. It provides insights into the effects of structure, size, and composition on the band gap.