Structural Chemistry and Excellent Nonlinear Optical Properties of a Series of Ternary Selenides Ga_<i>x</i>In_2–<i>x</i>Se₃

Abstract

Novel nonlinear optical (NLO) materials possessing simple chemical compositions and facile syntheses are competitive when considering their practical application. Here, a series of ternary selenides Ga_<i>x</i>In_2-<i>x</i>Se₃ (<i>x</i> = 0.07, 0.38, 0.45, and 0.81) that crystallize in a chiral <i>P</i>6₅ structure are obtained by melting Ga, In, and Se elements. Their three-dimensional structures are built by (Ga/In)Se₄ tetrahedra and InSe₅ trigonal bipyramids. The hexagonal modification's phase stability is analyzed by energy calculation, and their optical band gaps are determined to be 1.72-1.99 eV. They exhibit large NLO responses that are 1.41-1.64 times that of the benchmark AgGaS₂. The results of density functional theory calculations suggest that introduction of Ga onto the In site in (InSe₄)^5- units can form a deformed tetrahedron with more distortion in the structure, and the (InSe₅)^7- units contribute a large amount of birefringence to the structure. This work is the first to investigate the ternary chalcogenides M₂Q₃ (M = Ga or In; Q = S or Se) as new types of infrared NLO crystals with excellent performances, which will stimulate more interest in those possessing simple compositions and outstanding performances.