Room-temperature excitons in wide-gap layered-oxysulfide semiconductor: LaCuOS

Sharp optical absorption and emission peaks near the band gap ${\mathrm{(E}}_g\text{≈3.1\hspace{0.05em}}\mathrm{eV})$ were observed in LaCuOS polycrystalline thin films at room temperature. The absorption peak was able to be detected at temperatures as high as 490 K, and its intensity remarkably increased with decreasing temperature. The spectral position of the absorption peak and its temperature dependence almost agreed with those of the emission peak. It was concluded that the sharp absorption and emission peaks originate from excitons. On the basis of semiquantitative consideration about the excitons, it is suggested that the electronic-structure characteristic of the layered-crystal structure of LaCuOS is responsible for the stability of the excitons. The observation of the exciton absorption and emission at room temperature revealed that LaCuOS is a promising material for optoelectronic applications such as light-emitting devices.