Optical spectra of rare earth

Makovsky et al. (70) and Low (77, 72) succeeded in exciting optical-fluorescence spectra of rare earths and transition metals by means of X rays. All the crystals studied showed a wealth of fluorescent lines. In general, they observed emissions from 200 A in the ultraviolet to 20,000 A in the infrared. Many fluorescences were observed that could not be excited optically. By pulsing the X-ray source for 1 /xsec, they were able to measure decays from levels with the longer lifetimes. They point out that the X-ray beam could be pulsed for times on the order of 10 9 sec, thus allowing much shorter decay times to be measured. It is also possible to modulate the X-rays... 

The charge transfer spectra of rare earths in various media from which it is possible to obtain the optical electronegativity of the medium as proposed by Jorgensen (77, 12,) and Blasse and Bril 13). 

Breysse, M., B. Claudel, L. Faure and M. Guenin, 1978, Chemiluminescence induced by Catalysis, in The Rare Earths in Modem Science and Technology, eds. GJ. McCarthy and J.J. Rhyne (Plenum, New York) p. 99. Brousseau, B., F. Frandon, C. Colliex, P. Trebbia and M. Gasgnier, 1974, Energy Loss Spectra and Optical Constants of Rare Earth Metals, Hydrides and Oxides between 5 and 200 eV, in Vacuum UV Radiation Physics, eds. E. Koch, R. Haensel and C. Kunz (Per-gamon-Vieweg, Braunschweig) p. 622. Brundle, C.R. and A.D. Baker eds., 1978, Electron Spectroscopy Theory, Techniques and Applications, Vol. 2 (Academic Press, London). 

The optical spectra of in lanthanum trichloride (LaCh) are probably the most completely studied of those belonging to any host material. Dieke (1968) gives an excellent review of the experimental data and results of its analysis as of 1968 the results since 1969 have been summarized by Crosswhite (1977). The energy levels of the entire R series resulting from the experimental and theoretical analysis of the spectra of these ions in Lads have been presented by Dieke and coworkers at Johns Hopkins University in the form of a chart. These charts (Dieke and Crosswhite, 1963), Dieke Charts , have been invaluable in the analysis of the spectra of rare-earth ions in new host materials and have been practically a necessity in the technological application of rare-earth ions to lasers. The hygroscopic nature (Spedding and Daane, 1961) of LaCh has hindered the application of this material to practical devices such as lasers or quantum counters. 

Combined laser-microwave spectroscopy based on optical pumping was also performed in the solid state. Spectral line broadening caused, e.g., by strain and phonon interaction, can be overcome by extreme cooling and specific site selective procedures. Very narrow lines are attainable particularly in the spectra of rare earth ions doped to crystals in low concentration. Rare earth ions, therefore, play an important role in solid state spectroscopy, as will be illustrated in the course of this section. 

The optical transitions so typical of the spectra of rare earth (RE) within condensed phase usually correspond to intra-1 transitions of predominantly electric-dipole character. For a free ion, electric-dipole transitions between states of the same configuration are strictly parity forbidden, and thus any explanation of the observed spectra of glasses must concern itself with non-centro-symmetric interactions that lead to a mixing of states of opposite parity. This mixing may result from several distinct mechanisms. One of the most obvious mechanisms is simply the coupling of states of opposite parity by way of the odd terms in the crystal field expansion. 

Brousseau-Lahaye, B., F. Frandon, C. Colliex, P. Trebbia and M. Casgnier, 1974, Energy loss spectra and optical constants of rare earth metals, hydrides and oxides between 5 and 200 eV, in Vacuum UV Radiation Physics, eds E. 

Two general groups of atomic spectroscopic analytical techniques will be described in this chapter. Sections 1-5 will be devoted to techniques utilizing atomic spectra within or near the optical range of wavelengths. Section 6 will describe techniques which depend upon the X-ray spectra of the rare earth elements. The sharp line absorption and fluorescence spectra of rare earth ions in solution are not considered here, but are discussed in ch. 37A. 

Htifner S. Optical Spectra ofTransparent Rare-Earth Compounds. New York Academic Press, 1978 Inokuti M., Hirayama F. Influence of energy transfer by the exchange mechanism on donor Inmi-nescence. J. Chem. Phys 1965 43 1978-1989... 

The spectroscopic properties of lanthanide ions have already been the subject of several chapters in this series, The atomic lanthanide spectra and the theoretical methods for free-ion energy level calculation were reviewed by Goldschmidt (1978). Fulde (1979) considered the crystal fields in rare-earth metallic compounds. Attention was given to the determination of crystal-field parameters in opaque materials, for which no optical methods can be used. In a chapter concerning the complexes of the rare earths, Thompson (1979) paid attention to the spectroscopic properties of coordination compounds. Camall (1979) discussed the absorption and fluorescence spectra of rare-earth ions in solution. Weber s contribution (1979) treated rare-earth lasers and that of Blasse (1979) treated phosphors activated by lanthanide ions. Morrison and Leavitt (1982)... 

S. Hufner, Optical Spectra of Transparent Rare Earth Compounds, Academic Press, New York, 1978. 

Moreover, the analysis of the optical spectra of transition metal and rare earth ions is very illnstrative, as they present qnite different features due to their particular electronic configurations transition metal ions have optically active unfilled outer 3d shells, while rare earth ions have unfilled optically active 4f electrons screened by outer electroiuc filled shells. Because of these unfilled shells, both kind of ion are usually called paramagnetic ions. 

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

Most of the successful rare earth activated phosphors comprise host lattices in which the host cation is also a rare earth. A principal reason for this relates to the optical inertness of La, Gd, Y, and Lu this is essential to avoid interference with activator emission spectra. Close chemical compatibility including amenability to substitutional Incorporation of rare earth activators are also essential features. Rare earth hosts such as oxides, oxysulfides, phosphates, vanadates and silicates also tend to be rugged materials compatible with high temperature tube processing operations and salvage. 

Figure 9 Energy levels of some representative lanthanide tripositive ions. Ce and Pr, full set Eu and Tb, partial set (energy values taken from S. Hiifner, Optical Spectra of Transparent Rare Earth Compounds , Academic Press, 1978)...

Considerable attention has been paid in the past few years to the study of both the absorption and emission spectra of the rare earths. This has been boosted further by the development of the new branch of physics, the Laser (light amplification through stimulated emission of radiation). The study of the optical spectra of ions yields valuable information about the energy levels of normal configurations and of excited states, and also about the nature of their environment. However, a detailed analysis of optical spectra demands a considerable knowledge of theoretical techniques. Recent advances in paramagnetic resonance techniques [479] have enabled us to understand the nature of the ground states of the rare earth ions in crystalline environments. 

Ever since the foundations of spectroscopy were laid the problem of the relationship between the optical spectra emitted or absorbed by matter and the microscopic properties of the matter has been regarded as a fundamental problem. A class of very interesting systems with this regard is provided by non-metallic compounds of rare-earth ions with partially filled 4f shells. Their rich electronic structure is only weakly perturbed by the environment and provides a detailed fingerprint of the surrounding arrangement of atoms and their interactions with the f-electrons. 

The electron-phonon interaction has been studied also in a LiTnJA crystal by Kupchikov et al. (1982). They have measured Raman and infrared reflection spectra under pressures up to 1.2 GPa and at temperatures ranging from 4.2 K to 300 K. The interaction of optical phonons with electronic excitations in this system of rare-earth ions was detected by anomalous tem-... 

Hufner, S., 1978. Optical Spectra of Transparent Rare Earth Compounds. Academic Press, New York. Ihara, M., Igarashi, T., Kusunoki, T., Ohno, K., 2000. 

Emission of rare earth ions is due to the optical transition involving f levels (Tb3+ 4f8 Gd3+ 4f7 Eu3+ 4f7). The f electrons are well shielded from the chemical environment and f-f emission spectra consist of sharp lines. These optical transitions are generally slow within a time scale of microseconds to milliseconds because the f-f transitions are partially forbidden along with spin forbiddenness of many transitions. 

Studies on the s)mthesis mechanism as well as of the obtained nanocrystals of rare earth nanomaterials would inevitably boost further studies in s)mthesis and applications of these advanced materials. The in situ and ex situ investigation methods, including optical spectra, electrochemical devices, as well as modem combined microscopy techniques will reveal the underlying, yet currently unknown aspects of synthetic or catalytic chemical processes, where a true optimization or new design routes will be discussed. 

In principle, the applications of ICP-MS resemble those listed for OES. This technique however is required for samples containing sub-part per billion concentrations of elements. Quantitative information of nonmetals such as P, S, I, B, Br can be obtained. Since atomic mass spectra are much simpler and easier to interpret compared to optical emission spectra, ICP-MS affords superior resolution in the determination of rare earth elements. It is widely used for the control of high-purity materials in semiconductor and electronics industries. The applications also cover the analysis of clinical samples, the use of stable isotopes for metabolic studies, and the determination of radioactive and transuranic elements. In addition to outstanding analytical features for one or a few elements, this technique provides quantitative information on more than 70 elements present from low part-per-trillion to part-per-million concentration range in a single run and within less than 3 min (after sample preparation and calibration). Comprehensive reviews on ICP-MS applications in total element determinations are available. " ... 

The chemical behavior of the trivalent rare earths, the low magnetic ordering temperatures of most rare earth compounds with unfilled 4/ shells ), and the ligand hyperfine interactions observed in spin resonance measurements ) all indicate predominantly ionic behavior. This is presumably the result of the shielding of the 4/ electrons from the chemical environment by the 5s 5p shell. This shielding is also reflected in the narrow-line optical spectra of the trivalent... 

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