ACd4Ga5Te12 (A = K, Rb, Cs): Tellurides with a Strong Nonlinear Optical Response and Purple Emission

Chalcogenides are promising candidates for exploring mid- and far-infrared nonlinear optical (NLO) materials. Nevertheless, although tellurides possess greater advantages in the above-mentioned spectral regions, the reports on telluride NLO materials are far fewer than those on sulfides and selenides. In this work, a new quaternary NLO-active telluride, KCd4Ga5Te12, was discovered, and its Rb and Cs analogues were successfully synthesized. They are crystallized in the trigonal R3 space group and the structure features a 3D diamond-like framework constructed by vertex-sharing asymmetric MTe4 tetrahedra (centered by disordered Cd and Ga) that are stacked along the c-axis. Moreover, a comprehensive study of their IR NLO properties, photoluminescence properties, and structural features was performed. These compounds exhibited large powder second-harmonic generation (SHG) intensities, about 2.1 (2.7, 4.4) times that of AgGaSe2 in the particle size range of 20–50 (125–150) μm and a wide transmission range (∼25 μm). The SHG-density analysis revealed that the largest component χ333(2) of KCd4Ga5Te12 originates from three types of Te in the crystal structure. More importantly, it is rare in literature to demonstrate the consistency of linear and NLO properties calculated using both ultrasoft pseudopotentials and norm-conservation pseudopotentials. Besides, the title compounds also exhibit strong luminescence emissions around 420 and 470 nm at 298 K. This work implies that title compounds are promising candidates in the IR NLO applications.