Lanthanides laser properties

Of particular current interest are the fluorescence and laser properties of certain chelates of speciflc lanthanide ions (7, 5, 4> 44)- That a... 

Judd (1962) and Ofelt (1962) independently derived expressions for the oscillator strength of induced electric dipole transitions within the f configuration. This was a signal accomplishment. Much of the highly significant theoretical interpretation of the fluorescence process and the prediction of the properties of solid state lanthanide lasers, ch. 35, was made possible by this work. Since their results are similar, and were published simultaneously, the basic theory has become known as the Judd-Ofelt theory. However, Judd s expression, eq. (24.6), was cast in a form that could be directly related to oscillator strengths derived from lanthanide solution spectra, and he was the first to show that the model satisfactorily reproduced the experimental results for Nd (aquo) and... 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Another technique that uses the fluorescence properties of trivalent lanthanides is that of the detection of fluorescence emission decay induced by pulsed dye laser excitation. Horrocks and Sudnick (17) have applied this technique to the study of water molecules bound to metal ions in small complexes and proteins. In one study they found that the exponential decay of Tb3+ fluorescence is altered when H20 is replaced by D20 and that this change can be used to determine the number of coordinated water molecules on the metal ion. With thermolysin, bound Tb3+ had 1-2 water molecules in the first coordination shell. This number is consistent with the x-ray structure. 

This volume of the Handbook illustrates the rich variety of topics covered by rare earth science. Three chapters are devoted to the description of solid state compounds skutteru-dites (Chapter 211), rare earth-antimony systems (Chapter 212), and rare earth-manganese perovskites (Chapter 214). Two other reviews deal with solid state properties one contribution includes information on existing thermodynamic data of lanthanide trihalides (Chapter 213) while the other one describes optical properties of rare earth compounds under pressure (Chapter 217). Finally, two chapters focus on solution chemistry. The state of the art in unraveling solution structure of lanthanide-containing coordination compounds by paramagnetic nuclear magnetic resonance is outlined in Chapter 215. The potential of time-resolved, laser-induced emission spectroscopy for the analysis of lanthanide and actinide solutions is presented and critically discussed in Chapter 216. 

Lanthanides activated luminescent materials are widely used for solid-state lasers, luminescent lamps, flat displays, optical fiber communication systems, and other photonic devices. It is because of the unique solid-state electronic properties that enable lanthanide ions in solids to emit photons efficiently in visible and near IR region. Due to the pioneer work by Dieke, Judd, Wyboume, and others in theoretical and experimental studies of the... 

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]. 

Modem methods for study of metal-activated enzymes include NMR and ESR spectroscopy, water relaxation rates by pulsed NMR (PRR), atomic absorption, Mbssbauer, X-ray and neutron diffraction, high-resolution electron microscopy, UV/visible/IR spectroscopy, laser lanthanide pertubation methods, fluorescence, and equilibrium and kinetic binding techniques. Studies with Mg(II)-activated enzymes have been hampered by the lack of paramagnetic or optical properties that can be used to probe its environment, and the relative lack of sensitivity of other available methods initial velocity kinetics, changes in ORD/CD, fluorescence, or UV properties of the protein, atomic absorption assays for equilibrium binding, or competition with bound Mn(II) °. Recent developments in Mg and 0-NMR methodology have shown some promise to provide new insights . ... 

The spectroscopic properties of the lanthanides and actinides as they relate to laser action are the principal... 

Both f-f and f-d transitions have been used for lanthanide and actinide lasers. The spectroscopic properties of these transitions are compared in Table I. Since the d states have shorter lifetimes, faster pumping as well as higher energies are required for excitation. Possible pumping sources include ultrafast flashlamps, other lasers, electron beams, or synchrotron radiation, with one exception, all lanthanide and actinide lasers have been optically pumped. 

The spectroscopic properties and chemistry of aprotic Nd + laser liquids plus references to earlier studies are discussed by Brecher and French (V7). The oscillator strengths and fluorescence lifetimes are comparable to those in solids with quantum efficiencies near unity. Since fluorescence line-widths are smaller than in glasses, the stimulated emission cross sections are larger (1 8), although still less than in crystals. Aprotic liquid laser materials and references are listed in Ref. 19. Thus far only Nd3+ has been used as the laser ion although other lanthanide ions could also be used. 

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