Lanthanide colors

Relativistic effects are cited for changes in energy levels, resulting in the yellow color of gold and the fact that mercury is a liquid. Relativistic effects are also cited as being responsible for about 10% of lanthanide contraction. Many more specific examples of relativistic effects are reviewed by Pyykko (1988). 

Both arsonic and arsinic acids give precipitates with many metal ions, a property which has found considerable use in analytical chemistry. Of particular importance are certain a2o dyes (qv) containing both arsonic and sulfonic acid groups which give specific color reactions with a wide variety of transition, lanthanide, and actinide metal ions. One of the best known of these dyes is... 

Lanthanide nitridoborates can be divided into three classes salt-like compounds, semiconductors, and conductors or superconductors, as already shown in Fig. 8.7. Salt-like structures are usually transparent materials, marked by the typical color of the lanthanide ion. Here we discuss only nitridoborate compounds of lanthanum. The compounds La3(B3N, ) [27], La5(B3N, )(BN3) [28], Lag(B3N6)(BN3)N [29], and La3(BN3)N all count as salt-like materials, with La, ... 

Gruehn et al. [42] have reported on the isomorphy between modifications of LaTa309 and CeTajOg. Both contain trivalent lanthanide ions. The former is white, the latter is orange (P-modification), brass (O-modification) or yellow (M-modification). These colors are due to Ce(III)-Ta(V) MMCT absorptions, the Ce(III) and tantalate chromophores absorbing only in the ultraviolet. No doubt there are many more examples of this type in the literature. 

Pigments, minerals, gemstones, glasses, and many related materials are colored by impurity defects that absorb some of the incident white light, leaving a depleted spec-hum to color the solid. Colors in these materials are thus characterized by the absorption spectrum of the solid. Common inorganic colorants are the transition-metal and lanthanide metal ions. The colors ate characteristic of the ions themselves and are due... 

The lanthanides have electrons in partly filled 4/orbitals. Many lanthanides show colors due to electron transitions involving the 4/orbitals. However, there is a considerable difference between the lanthanides and the 3d transition-metal ions. The 4/ electrons in the lanthanides are well shielded beneath an outer electron configuration, (5.v2 5p6 6s2) and are little influenced by the crystal surroundings. Hence the important optical and magnetic properties attributed to the 4/ electrons on any particular lanthanide ion are rather unvarying and do not depend significantly upon the host structure. Moreover, the energy levels are sharper than those of transition-metal ions and the spectra resemble those of free ions. 

Glasses are frequently colored with transition-metal ions such as Mn2+, Ni2+, Co2+, lanthanides, or actinides.2 The addition of Co2+ impurities to silica glass leads to a... 

These materials are normally colored by low concentrations of 3d transition-metal ions or more rarely by lanthanide ions. The pale green color of ordinary window glass is due to the presence of Fe2+ impurities and small amounts of doping of Cr3+ into AI2O3 (corundum) creates ruby. 

The colors are characteristic of the ions themselves and are due to transitions between the partly filled d orbitals of transition metals (d-d transitions) or the partly filled / orbitals of lanthanides (f-f transitions). In the 3d transition-metal ions, the 3d orbitals contain one or more electrons. When these ions are introduced into a solid, the orbital energies are split by interactions with the surrounding anions. The color observed is due to transitions between these split energy levels. The color observed varies considerably as the interactions are dependent upon the... 

The basis for the claim of discovery of an element has varied over the centuries. The method of discovery of the chemical elements in the late eightenth and the early nineteenth centuries used the properties of the new sustances, their separability, the colors of their compounds, the shapes of their crystals and their reactivity to determine the existence of new elements. In those early days, atomic weight values were not available, and there was no spectral analysis that would later be supplied by arc, spark, absorption, phosphorescent or x-ray spectra. Also in those days, there were many claims, e.g., the discovery of certain rare earth elements of the lanthanide series, which involved the discovery of a mineral ore, from which an element was later extracted. The honor of discovery has often been accorded not to the person who first isolated the element but to the person who discovered the original mineral itself, even when the ore was impure and that ore actually contained many elements. The reason for this is that in the case of these rare earth elements, the earth now refers to oxides of a metal not to the metal itself This fact was not realized at the time of their discovery, until the English chemist Humphry Davy showed that earths were compounds of oxygen and metals in 1808. 

In the last (17th) position in the lanthanide series, lutetium is the heaviest and largest molecule of all the rare-earths as well as the hardest and most corrosion-resistant. It has a silvery-white color and is somewhat stable under normal atmospheric conditions. 

In many inorganic pigments, lanthanides and transition elements are responsible for color. Metal oxides and oxide hydroxides are, however, also important as colored pigments because of their optical properties, low price, and ready availability. Colored pigments based on oxides and oxide hydroxides are either composed of a single component or mixed phases. In the latter, color is obtained by incorporation of appropriate cations. 

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