Crystal Growth and First-Principles Calculations of the Mid-IR Laser Crystal Dy³⁺:PbGa₂S₄

A Dy³⁺-doped PbGa₂S₄ crystal with low phonon energy has been proved to be able to achieve the direct lasing of a mid-infrared laser. The single-crystal growth of Dy³⁺:PbGa₂S₄ was investigated in this work. On the basic of the high-purity polycrystalline material synthesized using a pressure-assisted method, a Dy³⁺:PbGa₂S₄ single crystal with φ 21 × 50 mm³ was successfully grown using the Bridgman method with a crucible–capsule technique. To understand the cleavage character of the PbGa₂S₄ crystal and get further insight into its electronic and phonon properties, the electronic, phonon, and mechanical properties of the PbGa₂S₄ host were investigated using first-principles calculations. PbGa₂S₄ exhibits not only a large electronic energy gap (2.76 eV) but also a low phonon energy (392 cm^–1) due to the incorporation of heavy Pb atoms between the interlayers. The high-frequency phonon bands of PbGa₂S₄ are mainly contributed by the vibrations of Ga–S atoms in the layer network formed by GaS₄ units. However, the weak Pb–S bonding connecting the alternating layers results in cleavage behavior of the PbGa₂S₄ crystal. We believe that the results of this paper could provide useful references for preparing or designing new chalcogenide hosts for mid-infrared lasers.