RESUMO
Multinary rare-earth chalcogenides with d-block transition metals have attracted considerable attention owing to their intriguing structural architectures and promising practical applications. In this work, three quaternary rare-earth sulfides, Ba4RE2Cd3S10 (RE = Sm, Gd, or Tb), have been obtained by the high-temperature solid-state method. These compounds are isostructural and belong to the noncentrosymmetric orthorhombic space group Cmc21 (No. 36). The basic structural unit contains unique two-dimensional anionic [RE2Cd3S10]8- layers, which are separated by Ba2+ cations. Remarkably, Ba4Sm2Cd3S10 exhibits a high second-harmonic-generation intensity (1.8 times that of AgGaS2) and a significantly higher laser-induced damage threshold (14.3 times that of AgGaS2), which is the first case possessing an infrared (IR) nonlinear optical (NLO) property in the quaternary AE/RE/TM/Q (AE = alkaline-earth metals; RE = rare-earth metals; TM = d-block transition metals; and Q = chalcogen) systems. Moreover, theoretical investigations of the structure-property relationship indicate that the combined action of various types of NLO-active units makes the main contribution to the SHG activity. This discovery may shed light on broadening the frontiers of IR-NLO materials.
RESUMO
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 (Eg) and large second-harmonic generation (SHG) efficiency (dij) 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 Eg, strong dij, 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 [RaXb][GanQ2n] 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.
