Lighting applications, lanthanide ions

The unique luminescent properties of rare earth metal clathrochelates have been used in the development of luminescent materials (luminophores and laser materials). The luminescence of these clathrochelates in solution makes their application as biological probes and concentrators of the luminescence (i.e., the antenna effect ) promising. These complexes can also serve as efficient molecular devices to convert UV light absorbed by the ligand to lanthanide ion luminescence in the visible region. Even in very dilute (10-5 mol l-i) solutions, the conversion of irradiated photons to luminescent ones has been observed to occur at a rate of approximately 1%. For rare earth metal aqua ions at the same concentration, the efficiency of conversion is equal to 4 x IQ- % [212, 390-392]. 

Electrical excitation of lanthanide ions has been commonly used in luminous discharge lamps and thin-film electroluminescent displays for a long time [1]. Presently, the utilization of lanthanides in different variants of light emitting diodes has attracted plenty of interest [2,3]. In these fields, mainly Eu ", Tb ", Sm ", Dy ", and Tm " with 4f —> 4f transitions are utilized, but some applications have also used Eu ", Ce ", and Yb " displaying 5d 4f transitions. 

The redox reaction has been utilized in the separation of light actinide elements (U, Np, and Pu) with both ion-exchange process and solvent extraction process. For trivalent heavy actinides with Z> 94 (except No), separation of these actinide ions from lanthanide ions is required for safe storage of long-lived nuclear waste and transmutation of these nuclides. Fundamental researches have widely been carried out by several groups for the purpose of quantitative separation of transuranium elements. Recent topics on the development and application of solvent extraction for the separation of transuranium elements are briefly summarized below. 

Apart from the applications derived from lighting and color reproduction, the next important application is laser. The Nd YAG laser is certainly one of the most widespread laser. The emission of Nd + in the NIR region thus also gives a good example of a lanthanide ion with an NIR emission, but as it will be shown, many other lanthaiude ions have a transition in the NIR. When it comes to NIR enussion, one could also wonder if an NIR absorption is achievable, and foremost, if such an absorption may yield a visible emission. Such an excitation is counterintuitive because it does not conserve the photon energy. Nevertheless, if two or more photons were absorbed, a conversion of two or more NIR photons to one visible photon may occur. The phenomenon (called upconversiori) is indeed observed under special conditions that will be discussed. 

The luminescence of the lanthanide ions spreads from the UV spectral range up to the NIR, and many lanthanide ions have unique spectral characteristics in the visible region of the spectrum, which also give them distinctive luminescent colors. A lot of applications take advantage of those characteristic emissions for color reproduction and lighting. Phosphors, nanomaterials made of lanthanide complexes or enclosing lanthanide compounds, as well as LEDs based on lanthanide complexes are extensively investigated. 

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