Effective photosensitized, electrosensitized, and mechanosensitized luminescence of lanthanide complexes

The 4f–4f emission of Tb(III), Eu(III), and Sm(III) complexes plays an important role in the design of monochromatic green, red, and deep-red luminescent materials for displays, lighting, and sensing devices. The 4f–4f emission of Yb(III), Nd(III), and Er(III) complexes is observed in the near-infrared (IR) region for bioimaging and security applications. However, their absorption coefficients are extremely small (ε < 10 L mol−1 cm−1). In this review, photosensitized luminescent lanthanide(III) complexes containing organic chromophores (ligands) with large absorption coefficients (ε > 10,000 L mol−1 cm−1) are introduced. Organic molecular design elements, including (1) the control of the excited triplet (T1) state, (2) the effects on the charge-transfer (CT) band, and (3) the energy transfer from metal ions for effective photosensitized luminescence, are explained. The characteristic electrosensitized luminescence (electroluminescence) and mechanoluminescence (triboluminescence) of lanthanide(III) complexes are also explained. Lanthanide(III) complexes with well-designed organic molecules are expected to open avenues of research among the fields of chemistry, physics, electronics, and material science. Lanthanide complexes can be made strongly luminescent by designing their ligands so that they act as antenna, find researchers in Japan. With their long luminescence lifetimes and narrow emission bands, lanthanide ions are attractive components for monochromatic luminescent materials. But their low light absorption hinders their widespread use. Yasuchika Hasegawa and co-workers from Hokkaido University, review how this problem can be overcome through using coordinating ligands as antennas. Such ligands absorb incident light and transfer its energy to the lanthanide ion. The researchers emphasize the importance of organic ligands’ excited triplet states and charge-transfer processes. They also discuss cases where luminescence is induced electrically or mechanically (for example, by grinding). The improved luminescence efficiency of such coordination complexes show promise for applications such as displays, solar cells and biomedical sensors. In this paper, the design strategy of trivalent lanthanide (Ln(III)) complexes for effective photo-, electric-, and tribo-sensitized luminescence are reviewed. Ln(III) complexes with well-designed organic molecules are expected to open up a frontier field of chemistry, physics, electronics and material science.