Rare earth atomic emission

Figure 2. Profiles of some rare earth atomic emission lines in inductively coupled plasma atomic emission spectrometry (photographic measurements obtained with a high-resolution grating spectrograph theoretical resolving power 460000 [12]...

The copious generation of TEs in OLEDs (Eq. (2)) has motivated the recent successful development of OLEDs based on electrophosphorescence, i.e., on the radiative decay of TEs in molecules containing a heavy transition metal or rare-earth atom, where that decay is partially allowed due to strong spin-orbit coupling.40,41 42 Although in the most recent study42 it was shown that some of the emission was due to triplet-triplet annihilation to SEs,... 

Rare earth compounds are excellent chromophores that exhibit intense emission with a narrow spectral bandwidth (full width at half-maximum of 5-20 nm) and relatively long decay lifetime (10 2-10 6 s) [58]. Since the emission from rare earth ions originates from transitions between the f levels of rare earth atom that are well protected from environmental perturbations by the filled 5s2 and 5p6 orbitals, the resulting emission spectra are expected to be sharp and narrow. They are the most widely used materials in inorganic light-emitting diodes [59]. A great deal of effort has also been devoted... 

The arc and spark spectra of the individual lanthanides are exceedingly complex. Thousands of emission lines are observed. For the trivalent rare-earth ions in soUds, the absorption spectra are much better understood. However, the crystal fields of the neighboring atoms remove the degeneracy of some states and several levels exist where only one did before. Many of these crystal field levels exist very close to a base level. As the soUd is heated, a number of the lower levels become occupied. Some physical properties of rare-earth metals are thus very sensitive to temperature (7). 

The total cerium content in the single crystal samples on the basis of rare-earth elements is determined by photometry after Ce(III) oxidation by ammonium persulfate. The Ce(III) content is calculated from the difference. Comparison of the determination results of the total cerium content obtained by photometric and atomic emission methods for Li GdlBO ljiCe demonstrated the elaborated procedure precision and systematic error absence. 

Elution volume calibrations were performed using radioactive tracers of the rare earth elements and 133Ba, with atomic-absorption or flame-emission analysis of iron, sodium, potassium, calcium, and magnesium. As shown in Fig. 5.14, any barium added to the second columns is eluted at the start of the light rare earth element fraction . To ensure barium removal the sample can be put through the first column again. 

The monazite structure consists of distorted PO4 tetrahedra with each metal atom roughly equidistant from nine oxygen atoms. Minor amounts of other rare-earth elements may occur. Steady-state liuninescence under X-ray excitation of monazite revealed emission of Gd, Tb, Dy and Sm (Gorobets and Rogojine 2001). Laser-induced time-resolved liuninescence enables us to detect Sm +, Eu and Nd emission centers (Fig. 4.70). 

It is interesting to note that the emission spectra of the terbium chlorides solvated with H20 and D20 show no discernible differences. Since the rare-earth chlorides solvated with D20 are isostructural with the chlorides solvated with H20 and since the emission spectra are essentially identical, Freeman et al believe that the variations in lifetime are not brought about by changes in the radiative-transition probabilities, but are a consequence only of changes in radiationless quenching efficiencies. They speculate that the decreased efficiency upon substitution of D20 for H20 must be related to the large changes in vibrational frequencies associated with substitution of the H atoms by the D atoms. 

M. I. Rucandio, Determination of lanthanides and yttrium in rare earth ores and concentrates by inductively coupled plasma atomic emission spectrometry. Anal. Chim. Acta, 264(2), 1992, 333-344. 

The importance of the work function and temperature of the surface, the ionization potential for positive ion emission, and the electron affinity for negative ion emission are well established for conditions in which the S-L equations are valid. Experimentally, the IP and EA are also important for thermal emitters. For example, the alkali metals all have low IPs and are emitted in good yields from the zeolites impregnated with the corresponding alkali metal. The halide and perrhenate anions all have high EAs and are emitted in good yield from certain of the rare earth oxides. The temperature is also quite important, but possibly not for the same reasons as for the S-L conditions. Under S-L conditions a higher temperature is more likely to strip an electron or to add an electron to an atom. 

Yttrium and rare earths were determined by atomic absorption lanthanum was determined by flame emission. Not determined. 

The following elements have better detectability in simple solutions by flame emission techniques compared with atomic absorption techniques Ca, Ba, Y, La, W, Re, Ir, In, Al, Sn, most rare earths, all alkali metals. 

C. R.J. Conzemius, Analysis of rare earth matrices by spark source mass spectrometry 377 37D. E.L. DeKalb and V.A. Eassel, Optical atomic emission and absorption methods 405 37E. A.P. D Silva and V.A. Eassel, X-ray excited optical luminescence of the rare earths 441 37E. E.W.V. Boynton, Neutron activation analysis 457... 

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. " ... 

Broekaert J. A. C., Leis F. and Laqua K. (1979) Some aspects of matrix effects caused by sodium tetraborate in the analysis of rare earth minerals with the aid of inductively coupled plasma atomic emission spectrometry, Spectrochim Acta, Part B 34 167-175. 

K. Yoshida and H. Haragacfai, Determination of rare earth elements by liquid chromatography/ inductively coupled plasma atomic emission. Anal Chem., 56,1984. 

Recently, hnes of a new type have been observed in the rare earth X-ray spectra, after an excitation -, the initial state of this transition is a highly excited neutral atom where a 3d electron is promoted to one of the empty/states depending on the dipolar transition probabiHties. This electron can come back to its initial 3 d level by a monoelectronic radiative transition. These emissions are in coincidence with a strong absorption peak and are interpreted as a resonance radiation 11). We have labeled these resonance lines (or R lines). They correspond to the 3d 4/" 3d 4/ radiative transition which is the reverse of absorption. 

Then, the conduction band structure of an actinide metal appears to be more complicated than that of a transition or rare earth metal because some 5/states are hybridized with the 6 d band. According to A. J. Freeman, for the hghter actinides up to Pu, the degree of the overlap between the 5/wave functions on neighbouring atoms is large thus the bandwidth, because of overlap and the hybridization with the 6d—l s bands, is noticeable. This seems to be in disagreement with the presence of R lines in the My and Mjy emission spectra. Indeed, the R lines involve 5/ states normally empty in the unperturbed metal, and information on the localization of only 5/excited states is obtained by their observation and not on that of 5/states situated below the Fermi level. 

---