Hg-Based Infrared Nonlinear Optical Material KHg₄Ga₅Se₁₂ Exhibits Good Phase-Matchability and Exceptional Second Harmonic Generation Response

Abstract

High-performance infrared (IR) nonlinear optical (NLO) materials with large NLO response and suitable birefringence are urgently needed for various applications. A Hg-based IR NLO material KHg4Ga5Se12 with such desirable properties has been newly discovered. In the structure, obviously distorted HgSe4 and GaSe4 tetrahedra are connected to each other by vertex-sharing to form a three-dimensional framework with the counterion K+ residing in the cavities. Remarkably, all the NLO-active building units in the title compound are arranged in a completely parallel manner. Such a topological structure and the large susceptibility of the Hg–Se bonds enable the material to achieve good phase-matchability with a tremendous powder second harmonic generation (SHG) response at 2.09 μm that is about 20-times that of the benchmark material AgGaS2 (one of the largest responses among all the phase-matchable IR NLO chalcogenides reported to date). The optical band gap of KHg4Ga5Se12 was determined as 1.61 eV. Moreover, on the basis of the electronic band structure, the real-space atom-cutting analysis, the SHG-weighted electronic densities, and the local dipole moments calculations, the origin of the superior linear and nonlinear optical properties of the title compound is ascribed to the (Hg/Ga)­Se4 group. The calculated values for the maximum coefficient d 33 and birefringence (Δn) at 2.09 μm are −65.257 pm/V and 0.072, respectively. Such values agree well with experimental observations. Our study demonstrates that Hg-based metal chalcogenides are a class of IR NLO material with competitive features (good phase-matchability, very large SHG efficiency, wide transparency) desirable for practical applications.

Ionothermal Synthesis of Metal Chalcogenides M2Ag3Sb3S7 (M = Rb, Cs) Displaying Nonlinear Optical Activity in the Infrared Region

“…19 Metal chalcogenides, on the other hand, have proven to be one of the best candidates for NLO materials in the MFIR regions, and so extensive efforts have been invested to discover new metal chalcogenides with useful MFIR NLO properties. [20][21][22][23] A great number of metal chalcogenides with large NLO properties have been synthesized and characterized thus far, such as commercial AgGaS 2 24 and AgGaSe 2 , 25 but each of these candidate chalcogenides has serious disadvantages including low laser damage threshold, strong (and deleterious) two-photon absorption, lack of phase-matchability at 1 μm, and difficulties in growing large-scale high-quality pure crystals. The development of new effective IR NLO materials remains an important contemporary challenge.…”

Infrared nonlinear optical sulfide CsCd4In5S12 exhibiting large second harmonic generation response

“…Constructed by oriented stacking FBUs and alkali ions, the compounds AX II 4 X III 5 Q 12 (A = K + , Rb + , Cs + ; X II = Zn 2+ , Cd 2+ , Hg 2+ ; X III = Ga 3+ , In 3+ ; Q = S 2− , Se 2− , Te 2− ) draw our attention. 41 Although some of the compounds in this system 12,34,35,41,42 such as KCd 4 Ga 5 S 12 , RbCd 4 Ga 5 S 12 and CsCd 4 Ga 5 Se 12 have been reported and showed strong powder SHG response with large LIDTs, most KCd 4 Ga 5 S 12 -type materials are confined in application due to phase mismatch. Moreover, it is difficult to synthesize the compounds AX II 4 In 5 S 12 due to the presence of the easily formed X II In 2 S 4 .…”

“…34 Meanwhile, enhancing the distortion degree of FBUs and diversifying asymmetric FBUs can effectively improve the formation possibility of NCS structures with large SHG response, which is observed in KHg 4 Ga 5 Se 12 disordered by Hg and Ga with a large SHG effect. 35 In general, the LIDT and the SHG coefficient are restricted by each other in view of their inversely proportional relationship with the energy band gap. 36,37 Introducing alkali or/and alkaline earth metal cations into the structure is a common method to enlarge the E g .…”

“…34 Meanwhile, enhancing the distortion degree of FBUs and diversifying asymmetric FBUs can effectively improve the formation possibility of NCS structures with large SHG response, which is observed in KHg 4 Ga 5 Se 12 disordered by Hg and Ga with a large SHG effect. 35…”

Li7Cd4.5Ge4Se16 and Li6.4Cd4.8Sn4Se16: Strong Nonlinear Optical Response in Quaternary Diamond‐Like Selenide Networks

“…Today,m aterial designs based on exploiting asymmetricb uilding units, such as distorted tetrahedra (GaS 4 ,G eS 4 ), p-conjugated trigonal planes ([HgSe 3 ] 4À ), MQ n polyhedra (M = second-order Jahn-Teller distorted d 0 and d 10 metal centers,e .g.,T a 5 + ,Z r 4 + ,C d 2 + ;Q = chalcogen), and some polar anionic groups with stereochemically active lone pairs ([AsS 3 ] 3À ,[ SbS 3 ] 3À ,[Te S 3 ] 2À ), has been enabled by broad-based advances in the understanding of synthesis and characterization methodology. [13][14][15][16][17][18][19][20][21] Furthermore, the diversity of asymmetric building units in as tructure would increase the difficulty of spontaneously producing am irror plane or inversion centerd uring the packing process,w hich in turn may promote the generation of an NCS structure, as explained by BaGa 2 MQ 6 (M = Si, Ge, Sn;Q = S, Se), Ba 23 Ga 8 Sb 2 S 38 , A 3 Ta 2 AsS 11 (A = K, Rb), ands oo n. [22][23][24][25][26][27][28] Consequently,t oo btain NCS structures with strongN LO responses, we are interested in exploring structures that contain two types of asymmetric buildingu nits.…”