Lanthanide Hexacyanidoruthenate Frameworks for Multicolor to White-Light Emission Realized by the Combination of d-d, d-f, and f-f Electronic Transitions.

We report an effective strategy toward tunable room-temperature multicolor to white-light emission realized by mixing three different lanthanide ions (Sm, Tb, and Ce) in three-dimensional (3D) coordination frameworks based on hexacyanidoruthenate(II) metalloligands. Mono-lanthanide compounds, K{Ln(HO)[Ru(CN)]}·HO (, Ln = La, = 3, = 1.2; , Ln = Ce, = 3, = 1.3; , Ln = Sm, = 2, = 2.4; , Ln = Tb, = 2, = 2.4) are 3D cyanido-bridged networks based on the Ln-NC-Ru linkages, with cavities occupied by K ions and water molecules. They crystallize differently for larger (, ) and smaller (, ) lanthanides, in the hexagonal 6/m or the orthorhombic mcm space groups, respectively. All exhibit luminescence under the UV excitation, including weak blue emission in due to the d-d T → A electronic transition of Ru, as well as much stronger blue emission in related to the d-f D → F transitions of Ce, red emission in due to the f-f G → H transitions of Sm, and green emission in related to the f-f D → F transitions of Tb. The lanthanide emissions, especially those of Sm, take advantage of the Ru-to-Ln energy transfer. The Ce and Tb emissions are also supported by the excitation of the d-f electronic states. Exploring emission features of the Ln-Ru networks, two series of heterobi-lanthanide systems, K{SmCe(HO)[Ru(CN)]}·HO ( = 0.47, 0.88, 0.88, 0.99, 0.998; -) and K{TbCe(HO)[Ru(CN)]}·HO ( = 0.56, 0.65, 0.93, 0.99, 0.997; -) were prepared. They exhibit the composition- and excitation-dependent tuning of emission from blue to red and blue to green, respectively. Finally, the heterotri-lanthanide system of the K{SmTbCe(HO)[Ru(CN)]}·2.5HO () composition shows the rich emission spectrum consisting of the peaks related to Ce, Tb, and Sm centers, which gives the emission color tuning from blue to orange and white-light emission of the CIE 1931 parameters of 0.325, 0.333.