Salt-inclusion chalcogenides: an emerging class of IR nonlinear optical materials

Abstract

Non-centrosymmetric metal chalcogenides such as AgGaS₂ and AgGaSe₂ are two of the commercial nonlinear optical (NLO) crystals widely used in the infrared (IR) region. Nevertheless, the inherent incompatibility between the wide energy gap (E_g) and large second-harmonic generation (SHG) efficiency (d_ij) hinders their high-power laser applications. Recently, the development of salt-inclusion chalcogenides with non-centrosymmetric structures has attracted more and more attention and interest owing to their intensive potential applications originating from their wide E_g, strong d_ij, ultrahigh laser-induced damage thresholds (LIDTs) and large IR transmission range. In this frontier paper, we review the recent progress of salt-inclusion chalcogenides (including 28 related compounds) as favourable candidates for IR-NLO materials, which can be divided into 3 types according to their chemical compositions and structural characteristics: (i) the [R_aX_b][Ga_nQ_2n] type and its derivatives, (ii) [NaBa₄Cl][Ge₃S₁₀] and its derivatives, and (iii) the [A₃X][MB₁₂(MQ₄)₃] type. The relationships between the non-centrosymmetric structures and NLO properties of these 3 types of compounds are summarized and briefly remarked. In addition, the present challenges of creating new IR-NLO salt-inclusion chalcogenides and future perspectives in this field are discussed.