Fig. 6. Core level X-ray photoemission spectra of (a) BiOCl on FTO glass showing the Bi³⁺ 4f_7/2 and 4f_5/2 transitions, with a minor Bi⁽⁰⁾ component at a lower binding energy. (b) Cl^– 2p_3/2 and 2p_1/2 transitions are also shown. (c) BiOBr on FTO glass showing the Bi³⁺ 4f_7/2 and 4f_5/2 transitions with a minor Bi⁽⁰⁾ component at a lower binding energy, along with the corresponding Br^– 3d_5/2 and 3d_3/2 transitions (d). (e) BiOI on FTO glass showing the Bi³⁺ 4f_7/2 and 4f_5/2 transitions with a minor Bi⁽⁰⁾ component at a lower binding energy, with I^– 3d_5/2 and 3d_3/2 transitions (f).