Lanthanide impurities

Meltzer et al. (2001) showed direct evidence for long-range interactions between lanthanide impurity ions in embedded nanocrystals with the TLS s of the matrix based on hole burning data. The samples were prepared as follows monoclinic 23 run Y2C>3 0.1% Eu3+ nanocrystals, produced by condensation after laser evaporation, were dispersed in a siloxane polymer. Fig. 13 shows the temperature dependence of the width of spectral holes (khb), which were burned in the 5Do <- 7Fo transition of Eu3+ ions located on the c sites (582.8 nm)innanociys-tals embedded in polymer, in comparison with the case of the free, as-prepared nanocrystals having the same size. The embedded nanocrystals exhibit a drastic increase in hole width and a very different power-law behavior for the temperature dependence of the hole widths relative to similar isolated nanoparticles. The 7 3 temperature dependence of the hole width... 

Washing the Precipitated Oxalates. As a result of the 2500-L heel of slurry left in the precipitation tank, the product slurry contained large concentrations of contaminating cations. To yield an acceptable product for downstream processing in MPPF, these ions had to be diluted from the product. Five equal volume washes of the slurry were calculated to reduce the non-lanthanide impurity concentrations of polyvalent cations to acceptable levels only four washes are needed to reduce the monovalent cations to acceptable levels as shown in Tables 1 and 2. 

Lanthanide impurity-ion spectra consist of a series of sharp lines that appear in groups of closely spaced sublevels that correspond to transitions between crystal-field split free-ion levels. The simplest absorption spectra occur at very low temperatures ( 4K), at which only the lowest Stark level is populated, in general. As the temperature is raised, transitions originating from thermally accessible excited levels are possible, thus complicating the spectrum. In fluorescence spectra, transitions arise at low temperature only from the lowest lying sublevel of the excited free-ion level. At higher temperatures, other transitions become possible. 

This situation is best illustrated by an example. Fig. 1 gives a partial energy level diagram for Nd LaCl (Dieke, 1968), which shows the splitting of the Fsp, ln/2, and I9/2 levels (all in cm" ) By the crystal field. The inp and sn levels, which are situated between the 1 3/2 and Iii/2 levels, are not shown. The crystal quantum numbers, i, are also shown these will be explained in section 2.2. The features illustrated in the figure are common to most lanthanide impurity-iop spectra, i.e. sharp levels in well-separated groups. 

Lanthanides in silicate rocks, commercial phosphoric acid, geological materials, refractory alloys, steel alloys, minerals, ores, monazite, and luminescent phosphors have been determined by HPLC. Determination of trace lanthanide impurities in nuclear grade uranium has been studied." An HPLC technique using the dynamic ion-exchange approach was also employed for the determination of Pm in urine. A typical application of lanthanide assay in nuclear industry is described next. 

Source From Determination of trace lanthanide impurities in nuclear grade uranium by coupled-column liquid chromatography, in Anal. Chem. ... 

Kondo-like behavior in dilute lanthanide impurity systems... 

The Kondo effect in a matrix-lanthanide impurity system in which the metallic matrix is a compound, rather than an element, was first discovered for the... 

Fig. 11.12. Reduced specific heat jump ACIACq vs reduced transition temperature TJT for (LaPr)Sn, alloys (solid circles and solid squares McCallum et al., 197Sa) and (LaSmjSn alloys (open circles DeLong et al., 1976). The solid line is derived from numerical calculations based on the theory of Keller and Fulde (1973) for crystal field-split lanthanide impurities in a superconductor. The BCS law of corresponding states behavior (dashed curve) and the AG behavior (dot-dashed curve) are shown for comparison. The negative deviations of the ACIACn vs TJT data from the AG curve are consistent with Kondo behavior (see fig. 11.10) for (I Sm)Sn3 alloys.

Dorenbos P (2009) Lanthanide charge transfer energies and related luminescence, charge carrier trapping, and redox phenomena. J Alloys Compd 488 568-573 Dorenbos P (2004) Locating lanthanide impurity levels in the forbidden band of host crystals. J Lumin 108 301-305... 

Dorenbos P (2004) Locating lanthanide impurity levels in the forbidden band of host crystals. J Lumin 108 301... 

The susceptibility of the RCoSn stannides (R=Y, Gd-Tm, Lu) has been measured between 78 and 293 K by Skolozdra et al. (1982). In this temperature range % obeys the Curie-Weiss law, except for YCoSn which is a Pauli paramagnet. The cobalt atoms are not magnetic. For LuCoSn /(T) is in accord with a modified Curie-Weiss law with iWeff = 0.79)tB. Apparently the presence of a magnetic moment in LuCoSn is caused by the presence of other lanthanides impurities (table 22). 

Mixed valence is usually investigated in intermetallic compounds where the lanthanide atoms are arranged in high concentration in a translationally invariant lattice. Mixed valence however occurs also in dilute lanthanide impurities in an otherwise normal matrix. Lm measurements were applied on dilute Ce, Pr, Nd, Sm,... 

Magnetic hyperfine field parameters for the lanthanide ions based on the results of Freeman and Watson (1962). The experimental free ion values of the total hyperfine field are derived from electron spin resonance data on dilute lanthanide impurities in insulators [Bleaney (1972)]. A positive sign for Htu means that the held has the same direction as the electronic moment. 

More generally, at arbitrary temperature and concentration of the lanthanide impurity ion, the dynamical consequences of the coupling of the two spin systems must be taken into account. The principal complication arises from the so-called bottleneck in the relaxation rate 3ie. This occurs when the rate of... 

Electron Correlation. Given the open-shell nature of the ground and excited states of lanthanide impurity ions in crystals, electron correlation is exU cmely important. Currently, electronic structure methods based on the use of multireference wavefunctions appear to be the fittest to respond to the requirements. Furthermore, their current evolution towards allowing more and more flexible definitions of the active space makes them even more adequate. Even though the methods used in the applications contained in this chapter are well known and their performance has been proven and documented in many highly correlated systems, we summarize here how to adapt them to the impurity lanthanide ion electronic structure demands. 

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