Ce4+/Ce3+ redox-controlled luminescence 'off/on' switching of highly oriented Ce(OH)2Cl and Tb-doped Ce(OH)2Cl films

The development of cerium (Ce) hosts and cerium-doped materials is required to meet the growing applications of cerium because cerium containing materials are attractive for many applications such as optical devices, fuel cells, gas sensors, oxygen adsorbents, and selective photocatalysts. In an effort to find new or little-known cerium compounds, Ce(OH)(2)Cl, a member of the RE(OH)(3-x)Cl-x (RE = rare earths) family, was successfully synthesized under ambient pressure. Based on the Rietveld structure refinement of the X-ray diffraction pattern, Ce(OH)(2)Cl crystallizes in the monoclinic space group P2(1)/m with unit cell parameters of a = 6.2898(2) (angstrom), b = 3.9456(1) (angstrom), c = 6.8680(2) (angstrom), and beta = 113.54(1) 1. The effective 4f -> 5d excitation of a Ce3+ ion in this compound caused a strong blue emission, which was attributed to electronic transitions from the 5d(1) excited state to the F-2(5/2) and F-2(7/2) levels of the 4f(1) ground state. Furthermore, Tb-doped Ce(OH)(2)Cl showed a strong green D-5(4) -> F-7(5) emission of Tb3+ upon excitation of Ce3+ ions due to the efficient energy transfer from Ce3+ to Tb3+ ions. In particular, the development of a synthetic route at ambient pressure allowed for simple deposition of Ce(OH)(2)Cl and Tb-doped Ce(OH)(2)Cl films. The growth direction of the film was significantly dependent on the substrate. The luminescence ` turn-off/on' switching was accomplished with highly oriented Ce(OH)Cl-2 and Tb-doped Ce(OH)(2)Cl films deposited on FTO glass. Both blue and green emissions could be reversibly quenched and restored by repeated oxidation and reduction in KMnO4 and ascorbic acid solutions, respectively. This Ce4+/Ce3+ redox-controlled luminescence 'off/on' switching was operated with a brightness change enough to see visually but without a significant degradation of crystal structure and surface morphology.