Dajiang Mei

Design and synthesis of a nonlinear optical material BaAl4S7 with a wide band gap inspired from SrB4O7

The most convenient method to generate mid-infrared (mid-IR) high-power lasers is through nonlinear optical (NLO) process using NLO materials with high laser damage threshold (LDT). The LDT is intrinsically dependent on the energy band gap, but often inverse of the NLO effect. Therefore, achieving a good balance between band gap (Eg > 3.0 eV) and NLO response (dij > 10 × KDP) in a good mid-IR NLO material is necessary. In this study, inspired by the oxide SrB4O7 with the highest LDT among all known borate crystals, we propose that the chalcogenide BaAl4S7 with similar crystal structure may have attractive NLO properties. The experiments revealed that BaAl4S7 possesses the broadest band gap (>3.95 eV) among all known mid-IR NLO chalcogenides, and its LDT is above 10 times that of the commercial material AgGaS2. Moreover, its NLO coefficient is above 10 × KDP (half of that of AgGaS2). All these features demonstrate that BaAl4S7 is a potential candidate as a good mid-IR NLO material.

Wide band gap design of new chalcogenide compounds: KSrPS4 and CsBaAsS4

Recently, the exploration of infrared nonlinear optical (IR NLO) materials has mainly focused on chalcogenide compounds. However, their practical applications are often hampered by the low laser damage thresholds (LDTs). It is known that wide band gaps can significantly enhance the LDTs of materials, and the introduction of alkali and alkaline earth cations would broaden the band gap. Accordingly, in this work two new compounds KSrPS4 and CsBaAsS4 with both alkali and alkaline earth cations were synthesized successfully. Both compounds crystallize in the space group Pnma (62) of the orthorhombic system, and the structures consist of isolated PnS4 (Pn = P, As) tetrahedra with the interstices occupied by K (or Cs) and Sr (or Ba) atoms, respectively. The band gaps of compounds were determined by different methods. The UV-visible diffuse reflectance spectra revealed that the band gaps of KSrPS4 and CsBaAsS4 are larger than 3.62 eV and 2.86 eV, respectively. The band gaps are primarily determined by the PnS4 tetrahedra.