Trivalent ions spectra

Among other examples, time-resolved luminescence has recently been applied to the detection of different trace elements (i.e., elements in very low concentrations) in minerals. Figure 1.13 shows two time-resolved emission spectra of anhydrite (CaS04). The emission spectrum just after the excitation pulse (delay 0 ms) shows an emission band peaking at 385 nm, characteristic of Eu + ions. When the emission spectmm is taken 4 ms after the pulse, the Eu + luminescence has completely disappeared, as this luminescence has a lifetime of about 10/rs. This allows us to observe the weak emission signals of the Eu + and Sm + ions present in this mineral, which in short time intervals are masked by the En + Inminescence. The trivalent ions have larger lifetimes and their luminescence still remains in the ms delay range. 

While the stoichiometries of the Mn SOD enzymes appear to vary, the properties of the Mn-binding site do not. This is borne out in the electronic spectra of these proteins, which display a great degree of similarity despite the diversity of sources from which they have been isolated (Table II). This type of spectrum is distinctive for manganese in the trivalent oxidation state (3). The native enzymes are EPR silent, as might be anticipated if they contained Mn solely as the trivalent ion (S = 2) (1, 6,12,18-20, 24). However, when the enzymes are denatured, the characteristic six-line pattern of Mn(II) (I = 5/2) appears. Magnetic susceptibility studies with the E. coli SOD were consistent with the presence of a monomeric Mn(III) complex with a zero-field splitting of 1 to 2 cm-1 (4). The enzymes are additionally metal specific (however, see Refs. 36 and 37) metal reconstitution studies with E. coli and B. stearothermophilus revealed a strict requirement for Mn for superoxide dismutase activity (2, 22, 23). 

Mixed oxides of Ce and other lanthanides (La, Nd) were studied by Kubsch et al. [133], who found segregation of these trivalent ions to the surface in samples calcined at 1253 K a high Eb peak in the 01s feature was observed, being ascribed to carbonates formed in the trivalent ion-rich surface. A tendency to formation of such mixed oxides was detected in (Ce,Tb)Ox supported on lanthana-promoted alumina after calcination the La XP spectrum displayed two components, ascribed to La species on the AI2O3 surface and dissolved into the Ce,Tb oxide respectively [146]. A high Eb Ols peak observed there was ascribed to both alumina 0 ions and carbonate species on La-rich zones while the (Ce,Tb) oxide gave lower Eb values. 

In europium metal and in a number of cubic chalcogenide compounds the europium ion is divalent, and NMR has been used to investigate the ordered state (see section 5.2)l Measurements have also been made on a number of trivalent ions in ordered insulating compounds. The precision obtainable is illustrated by Ho in the ferromagnet Ho(OH)3, where the spectrum is centred on 5013(1) MHz, and a pseudo-octupolar term w/j with w = 0.25 MHz is needed (see section 5.4) to fit the... 

In the nearest JR and visible regions every complex exhibits the spectrum, which is typical for the trivalent ion of the corresponding lanthanoid. 

Let us now consider MMCT for the case in which the donating ion is a lanthanide ion with a partly filled 4/ shell M(/")M(d°)CT. The trivalent lanthanide ions with a low fourth ionization potential are Ce, Pr ", Tb ". Their optical absorption spectra show usually allowed 4f-5d transitions in the ultraviolet part of the spectrum [6, 35]. These are considered as MC transitions, although they will undoubtedly have a certain CT character due to the higher admixture of ligand orbitals into the d orbitals. In combination with M(d°) ions these M(/") ions show MMCT transitions. An early example has been given by Paul [36] for Ce(III)-Ti(IV) MMCT in borosilicate glasses. The absorption maximum was at about 30000 cm ... 

Trivalent Co complexes of the mixed donor amino arsine emda (2-aminoethyl)dimethylarsine) have been synthesized.936 Examples include trans(X,X), cA(As,As)-[CoX2(edma)2]+ (X = C1, Br, and I), trans( As,As)- and trara(As,N)-[Co(acac)(edma)2]2+, trara(As,N)-[Co(C03)(edma)2]+, [Co(acac)2(edma)]+, and /ao[Co(edma)3]3+. The /ao[Co(edma)3]3+ complex was resolved and the absolute configuration of the (+)49o CD isomer was assigned as A on the basis of the CD spectrum. Racemization of this complex was first order in both complex and hydroxide ions. The crystal structure of [Co(acac)2(emda)]C104 has been reported.937... 

Raman spectra are usually represented by the intensity of Stokes lines versus the shifted frequencies 12,. Figure 1.15 shows, as an example, the Raman spectrum of a lithium niobate (LiNbOs) crystal. The energies (given in wavenumber units, cm ) of the different phonons involved are indicated above the corresponding peaks. Particular emphasis will be given to those of higher energy, called effective phonons (883 cm for lithium niobate), as they actively participate in the nonradiative de-excitation processes of trivalent rare earth ions in crystals (see Section 6.3). 

F ure 6.16 A typical absorption spectrum of a trivalent rare earth ion (not corresponding to any specific ion) in a crystal. A generic / —> / absorption transition, with an average frequency of mo, has been marked and shaded (see the text). 

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