Mixed-anion chalcogenide-halide semiconductors A 2 BaTaS 4 Cl (A = K, Rb, Cs) and K 2 BaNbS 4 Cl

-axis due to extended Cs and Ba ordering. Consistent with electronic structure calculations, the measured bandgaps of the Ta-based compounds are ∼3.0 eV while the Nb-based compounds exhibit a reduced bandgap of ∼2.5 eV, reflecting the lower energy of the Nb d orbitals.