BaGa2MQ6 (M = Si, Ge; Q = S, Se): a new series of promising IR nonlinear optical materials

Abstract

The four compounds BaGa(2)MQ(6) (M = Si, Ge; Q = S, Se) have been identified as a new series of IR nonlinear optical (NLO) materials and are promising for practical applications. They are isostructural and crystallize in the noncentrosymmetric polar space group R3 of the trigonal system. Their three-dimensional framework is composed of corner-sharing (Ga/M)Q(4) (M = Si, Ge; Q = S, Se) tetrahedra with Ba(2+) cations in the cavities. The polar alignment of one (Ga/M)-Q2 bond for each (Ga/M)Q(4) tetrahedra along the c direction is conducive to generating a large NLO response, which was confirmed by powder second-harmonic generation (SHG) using a 2090 nm laser as fundamental wavelength. The SHG signal intensities of the two sulfides were close to that of AgGaS(2) and those for the two selenides were similar as that of AgGaSe(2). The large band gaps of 3.75(2) eV, 3.23(2) eV, 2.88(2) eV, and 2.22 (2) eV for BaGa(2)SiS(6), BaGa(2)GeS(6), BaGa(2)SiSe(6), and BaGa(2)GeSe(6), respectively, will be very helpful to increase the laser damage threshold. Moreover, all the four BaGa(2)MQ(6) (M = Si, Ge; Q = S, Se) compounds exhibit congruent-melting behavior, which indicates that bulk crystals needed for practical applications can be obtained by the Bridgman-Stockbarger method. The calculated birefringence indicates that these materials may be phase-matchable in the IR region and the calculated SHG coefficients agree with the experimental observations. According to our preliminary study, the BaGa(2)MQ(6) compounds represent a new series of promising IR nonlinear optical (NLO) materials which do not belong to the traditional chalcopyrite-type materials such as AgGaQ2 (Q = S, Se) and ZnGeP(2).

Structure and properties of off-stoichiometric Ba–Ga–Ge selenide glasses

“…It was shown in previous studies of stoichiometric BGGS glasses [23,25] that glass formation is favored toward the edges of the ternary composition space-that is, toward pure GeSe 2 and the binary tie lines between Ga 2 Se 3 -GeSe 2 and BaSe-GeSe 2 , but away from the region near R = 1, i.e., BaSe:Ga 2 Se 3 = 1:1. A lack of glass formation near R = 1 was also observed in the analogous sulfide system BaS-Ga 2 S 3 -GeS 2 [17] and it suggests that in both the sulfide and selenide systems, devitrification near the center of the ternary diagram might be attributed to the existence of crystalline phases such as Ba 2.7 Ga 5.4 Ge 3.6 S 18 [16] and BaGa 2 GeX 6 (X = S, Se) [30,31], where the ratio of BaX:Ga 2 X 3 is 1:1.…”

Five New Chalcohalides, Ba3GaS4X (X = Cl, Br), Ba3MSe4Cl (M = Ga, In), and Ba7In2Se6F8: Syntheses, Crystal Structures, and Optical Properties

“…The Ba−Se distances range from 3.100(1) to 3.585(1) Å, shorter than those in BaGa 4 Se 7 (3.611(2) to 3.861(2) Å) 35 and BaGa 2 GeSe 6 (3.487(1) to 3.638(1) Å). 28 The Ba−Cl interatomic distances is 3.236(1) Å, resembling that of BaCl 2 (3.159(1) to 3.197(1) Å). 31 Crystal Structure of Ba 7 In 2 Se 6 F 8 .…”

“…The Ba−F band length is from 2.557(2) to 2.833(5) Å, much more dispersive than those of Ba 2 SnSe 3 F 2 (2.663(1) to 2.696(1) Å). 5 The Ba− Se distances vary from 3.399(1) to 3.649(2) Å, resembling those in BaGa 2 GeSe 6 (3.487(1) to 3.638(1) Å) 28 and shorter than those in BaGa 4 Se 7 (3.611(2) to 3.861(2) Å). 35 Structural Comparison.…”

K2Sn2ZnSe6, Na2Ge2ZnSe6, and Na2In2GeSe6: a new series of quaternary selenides with intriguing structural diversity and nonlinear optical properties

“…22 Generally speaking, a large macroscopic NLO response originates from the cooperative arrangement of the microscopic NLO building units, including the MX 4 tetrahedra (M = Ga, In, Si, Ge, Sn etc. ; X = S, Se), the polyhedra centered by the second-order Jahn-Teller (SOJT) distorted d 0 (e.g., Ta 5+ , Zr 4+ ) or d 10 radiation. The scanning step width of 0.05º and a fixed counting time 0.2 s/step were applied to record the patterns in the 2θ range of 10-70º.…”