Mid-Infrared Nonlinear Optical Halides with Diamond-like Structures: A Theoretical and Experimental Study

Abstract

As an important family of potential mid-IR nonlinear optical (NLO) crystals, halides exhibit superiority in large optical band gaps and wide IR transparency. However, their second-harmonic generation (SHG) effects are generally small, limiting their frequency conversion efficiency in NLO processes. Diamond-like structures, due to the intrinsic polarization-parallel alignment of tetrahedral frameworks, enable sufficiently large SHG effects while maintaining balanced NLO performance in the mid-IR spectral region. Accordingly, in this study, we focused on the NLO performance mining and assembly of tetrahedral polar motifs in halides with unique diamond-like structures. We screened almost all diamond-like structures in inorganic halide systems and investigated in detail how their balanced NLO performances evolve with ideal and defective diamond-like structures. We predicted that the three existing diamond-like iodides, CuGaI 4 , Ag 2 CdI 4 , and Ag 2 ZnI 4 , can satisfy the balanced requirement of strong SHG effects (>3.9 pm/V) and large optical band gaps (>3 eV) by analyzing the microstructural NLO origin. Preliminary experiments also verified our predictions with Ag 2 CdI 4 (1.4 × AgGaS 2 and 3.3 eV) and Ag 2 HgI 4 (2.2 × AgGaS 2 and 2.4 eV). More importantly, a map with the diamond-like halide family tree was illuminated, unlocking dozens of diamond-like structures with balanced NLO properties, from ternary AgCdI

Flexible UV photodetector based on copper tetraiodogallate (CuGaI4) film

“…To further investigate the optoelectronic properties of CuGaI 4 , the band structure was evaluated by density functional theory calculation. As depicted in Figure 1D, the conduction band minimum and the valence band maximum are localized in the same k-vector in the Brillouin zone, indicating that CuGaI 4 is a direct semiconductor with a 2.98 eV bandgap, 21 which is close to the experimental value.…”

AgIn5Se8: a defect diamond-like non-linear optical selenide

“…Furthermore, we highlighted metal chalcogenides and metal halides with diamond-like (DL) structures, in which the tetrahedral units were closely packed and can result in additive superposition of the microscopic second-order susceptibility. 21–23 This structural feature can further enhance the SHG response by introducing vacant sites in the lattice ( i.e. , forming the defect diamond-like structures) and would lead to higher SHG efficiency.…”

“…Furthermore, we highlighted metal chalcogenides and metal halides with diamond-like (DL) structures, in which the tetrahedral units were closely packed and can result in additive superposition of the microscopic second-order susceptibility. [21][22][23] This structural feature can further enhance the SHG response by introducing vacant sites in the lattice (i.e., forming the defect diamond-like structures) and would lead to higher SHG efficiency. After that, dozens of defect diamond-like chalcogenides and halides, such as Ga 2 S 3 , 24 Hg 2 GeSe 4 , 25 LiZnPS 4 , 26 and Ag 2 HgI 4 , 27 were reported as good candidates for mid-IR NLO applications.…”

Salt-inclusion sulfides [K4Cl][MII11In9S26] (MII = Zn, Cd) displaying robust nonlinear optical activity

“…In order to address this issue, extensive efforts have been made to create and develop various IR NLO crystals in different systems, including chalcogenides, oxides, oxychalcogenides, halides, and pnictides. [12][13][14][15][16][17][18][19] Among these systems, metal chalcogenides have emerged as promising NLO materials due to their diverse structures and appealing functional flexibility. According to the anionic group theory, the ''NLO-active functional motif'' has played a crucial role in being responsible for significant SHG responses, 20 such as the distorted tetrahedral [GaS 4 ] in BaGa 4 S 7 21 and LiGaS 2 , 22 trigonal planar [HgSe 3 ] in BaHgSe 2 , 23 and polyhedral [SbS n ] (n = 3, 5) in KSb 5 S 8 .…”