BaHgGeSe₄ and SrHgGeSe₄: Two New Hg-Based Infrared Nonlinear Optical Materials

Abstract

New practically usable infrared (IR) nonlinear optical (NLO) crystals, especially those suitable for highly efficient pumping of the commercial 1 μm laser, are in urgent demand. However, only a few new IR NLO materials have been grown into bulk crystals and realized IR laser output during the past 20 years due to the extreme difficulty in achieving the coexistence of various strongly correlated properties. In this work, on the basis of the bonding characteristics of the Hg element and an efficient screening strategy for high-performance new crystals, we identified two new Hg-based IR NLO materials, BaHgGeSe4 and SrHgGeSe4. They crystallize in polar space group Ama2 with the distorted HgSe4 and GeSe4 tetrahedra aligned in parallel. They exhibit exceptional balance in terms of all of the preferred properties for practical applications, especially for highly efficient pumping of the commercial 1 μm laser. Their large band gap (∼2.5 eV) can avoid the two-photon absorption of the 1 μm laser and increase the laser damage threshold. They are phase matchable with a very strong NLO response (5 × AgGaS2). They can cover the 3–5 and 8–12 μm atmospheric windows. Moreover, they melt congruently, which indicates that bulk crystals can be obtained by the Bridgman method. Their overall properties are better than those of the traditional AgGaQ2 (Q = S or Se) materials to a large degree. Detailed structural analysis and calculations elucidate the crucial role of cations in regulating the packing of the anionic groups and that of the highly polarizable HgSe4 in balancing optical properties.

Structural modification from centrosymmetric Rb4Hg2Ge2S8 to noncentrosymmetric (Na3Rb)Hg2Ge2S8: mixed alkali metals strategy for infrared nonlinear optical material design

“…17 Under the guidance of these ideas, high-performance IR NLO materials with tetrahedron [MQ 4 ] n − as the NLO functional motif have been extensively studied, such as BaGa 4 Q 7 (Q = S, Se), 18,19 BaGa 2 MQ 6 (M = Si, Ge; Q = S, Se), 20 M II 3 P 2 S 8 (M II = Zn, Hg), 21,22 and AM II M IV Q 4 (A = Eu, Sr, Ba; M II = Mn, Zn, Cd, Hg; M IV = Si, Ge, Sn; Q = S, Se). 23–28 A common strategy for broadening band gaps is introducing alkali or alkaline earth metals to these compounds. However, the interaction between alkali or alkaline earth metal cations and anions ( i.e.…”

AXHg3P2S8 (A = Rb, Cs; X = Cl, Br): New Excellent Infrared Nonlinear Optical Materials with Mixed‐Anion Chalcohalide Groups of Trigonal Planar [HgS2X]3− and Tetrahedral [HgS3X]5−

“…Among the various IR NLO‐active anionic groups, Hg‐based BBUs are very competitive due to several advantages: 1) Hg 2+ cation possesses highly polarizable and deformable electron cloud, which would significantly increase the second harmonic generation (SHG) effect and birefringence; [ 12 ] 2) multiple coordination modes of Hg exist including linear, trigonal‐planar, and tetrahedral geometries, which provide opportunities to construct novel structures. Many Hg‐based IR NLO crystals have been discovered recently in both halides and chalcogenides systems with strong SHG responses and wide bandgaps ( E g ), such as Na 2 Hg 3 Ge 2 S 8 (2.2 × AGS; 2.68 eV), [ 13 ] BaHgSe 2 (1.5 × AGS; 1.56 eV), [ 14 ] SrHgGeSe 4 (4.8 × AGS; 2.42 eV), [ 15 ] CuHgPS 4 (6.5 × AGS; 2.03 eV), [ 16 ] AgHgPS 4 (5.06 × AGS, 2.63 eV), [ 17 ] Cs 2 HgI 2 Cl 2 (1 × KDP; 3.15 eV), [ 18 ] and RbHgI 3 (7 × KDP; 2.56 eV). [ 19 ] Thereby, mixed‐anion [HgQ m X n ] BBUs are expected to exist and perform well.…”

Infrared nonlinear optical sulfide CsCd4In5S12 exhibiting large second harmonic generation response

“…The promising IR-NLO materials for applications should satisfy the following conditions: a high SHG coefficient, a large LIDT, a wide IR transmission range, phase matching behavior and high thermal stability. [19][20][21][22][23][24][25][26] However, it is difficult to maintain the balance among the above properties, which encourages the development of new structural design strategies for highperformance IR-NLO materials. Fundamental building units (FBUs), such as d 10 cationcentred tetrahedral anionic groups ([CdS 4 ] 6À , [HgS 4 ] 6À , [InS 4 ] 5À , [GaS 4 ] 5À , [GeS 4 ] 4À , etc.…”