Electronic structure and fundamental absorption edges of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated (001) surfaces of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals grown by the Bridgman method have been measured and fundamental absorption edges of the ternary bromides have been recorded in the polarized light at 300 K and 80 K. The present X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (001) surfaces of KxRb1−xPb2Br5 (x=0, 0.5, and 1.0) single crystals. Substitution of potassium for rubidium in KxRb1−xPb2Br5 does not cause any changes of binding energy values and shapes of the XPS constituent element core-level spectra. Measurements of the fundamental absorption edges indicate that band gap energy, Eg, increases by about 0.14 and 0.19 eV when temperature decreases from 300 K to 80 K in KPb2Br5 and RbPb2Br5, respectively. Furthermore, there is no dependence of the Eg value for KPb2Br5 upon the light polarization, whilst the band gap energy value for RbPb2Br5 is bigger by 0.03–0.05 eV in the case of E‖c compared to those in the cases of E‖a and E‖b.

► KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals were grown by the Bridgman method.
► High chemical stability of (001) surfaces is characteristic of the single crystals.
► There is no dependence of band gap energy, Eg, in KPb2Br5 upon light polarization.
► Eg in RbPb2Br5 is bigger by 0.03–0.05 eV for E‖c compared to those for E‖a, b.
► Eg increases in KPb2Br5 and RbPb2Br5 when temperature decreases from 300 to 80 K.