Here, the lanthanides and their complexes are introduced. We show you where you can find the lanthanides in the periodic table, how the lanthanide ions get their interesting photophysical properties and how this can lead to luminescent lanthanide complexes.
More information on the subject can be found in the references mentioned in the Luminescent Lanthanide Bibliography.
Remark: This description of 'the lanthanides' is based on the IUPAC (International Union of Pure and Applied Chemistry) definition. Dr. Binnemans pointed out that according to the Rare Earth Information Center (Ames, USA) also Lanthanum (no. 57) itself is a lanthanide.
Rare earth elements are separated from other elements in a mineral by precipitation with a suitable reagent. Separation of the rare earth elements from each other by ordinary chemical means is difficult because their chemical properties are similar, and the isolation of an individual element may involve hundreds of fractional crystallizations. With the use of ion-exchange methods the separation of an individual rare earth element can be accomplished with greater ease and precision. Oxides of the rare earth elements are called rare earths, and are found in minerals that are actually more abundant than those of some other metals, such as those in the platinum group. The principal source of rare earths is the mineral monazite. Some other rare minerals that also contain small amounts of rare earths include cerite, gadolinite, and samarskite
The f-f electronic transitions are forbidden, leading to long excited state lifetimes, in the micro- to millisecond range. The forbidden nature of the f-f transitions is also reflected in low extinction coefficients, making direct photoexcitation of lantahide ions difficult. This can be overcome by using energy transfer from organic chromophores to lanthanide ions. See also: "Luminescent Lanthanide Ions: Making Them Shine Brightly" (Sensitization of lanthanide luminescence).
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