Luminescent Ce(III) Complexes with Tunable Emissions

Luminescent lanthanide complexes, for example with cerium, can be useful, e.g., as inorganic phosphors or in photocatalysis. Cerium(III) usually exhibits a broad double-peak emission originating from two different electronic transitions. The option to adjust the bandwidth of emissions for different applications like lighting and displays would be useful. Systematically tuning the emission bandwidth of Ce(III) complexes could be possible by changing the ligands’ coordinating atoms.

Zhiwei Liu, Hong Jiang, Peking University, Beijing, China, and colleagues have developed a series of chalcogen-coordinated Ce(III) complexes with imidodiphosphinate ligands featuring bulky tert-butyl groups, i.e., complexes of the type Ce-E₂ip^tBu (pictured, E = O, S, Se, Te). The ligands were synthesized starting from ^tBu₂PCl, which was reacted with NaNH₂ to give ^tBu₂PNH₂, which undergoes a condensation to (^tBu₂P)₂NH.

The oxidation of (^tBu₂P)₂NH using H₂O₂, S₈, or Se gives the desired O-, S-, and Se-coordinating ligands, respectively. For the Te-coordinating ligand, it was necessary to deprotonate (^tBu₂P)₂NH with NaH first to drive the oxidation reaction with Te. Then, the Ce(III) complexes were obtained via a salt metathesis reaction. The four Ce(III) complexes were characterized using single-crystal X-ray crystallography and photoluminescence spectroscopy.

With the introduction of heavier chalcogen atoms, a new Ce(III) complex with orange-red emission beyond the traditional emission color regions of Ce(III) was obtained (using Te). In addition, the ratio of the two emission peaks could be systematically tuned, achieving the narrowest emission from Ce(III) with a full width at half maximum of 42 nm when using Te. Overall, the work provides insight into the design of luminescent Ce(III) complexes with multidentate soft-donor ligands and could promote their applications in both narrow-band displays and broad-band lighting.