Band gap engineering, band edge emission, and p-type conductivity in wide-gap LaCuOS1−xSex oxychalcogenides

The preparation of ${\mathrm{LaCuOS}}_{\text{1−x}}{\mathrm{Se}}_x$ solid solutions $\text{(x=0.0,}$ 0.25, 0.5, 0.75, and 1.0) was attempted to control their energy gap and band edge emission energy. X-ray diffraction analysis revealed that the lattice constant of ${\mathrm{LaCuOS}}_{\text{1−x}}{\mathrm{Se}}_x$ increased linearly with increasing x, indicating the formation of a complete solid solution in the LaCuOS–LaCuOSe system. The energy gap estimated from the diffuse reflectance spectra varied continuously from ∼3.1 eV for $\text{x=0}$ to ∼2.8 eV for $\text{x=1.}$ The sharp emission near the absorption edge was observed in all samples at room temperature under ultraviolet light irradiation. p-type electrical conduction in these materials was confirmed by Seebeck measurements, and the conductivity was enhanced by substitution of Sr for La. These results demonstrated that the formation of the solid solutions enabled band gap engineering in ${\mathrm{LaCuOS}}_{\text{1−x}}{\mathrm{Se}}_x$ oxychalcogenides keeping their band edge emission feature and p-type conductivity.