Color characteristics lanthanide ions

This chemical n-doping procedure can readily be extended to the lanthanide ions Eu and Yb. Europium and ytterbium metals are known to dissolve in liquid ammonia (19). They form solvated divalent cations and solvated electrons in ammonia with the characteristic blue color. Upon immersion of polyacetylene the solvated electrons spontaneously reduce the polyacetylene chains to polycarbanions and the divalent lanthanide ions become countercations to maintain charge neutrality. 

Because of ligand-field factors, certain transition metal ions, notably Cr + and Co +, almost exclusively exhibit a coordination number of six in their complexes. The kinetically inert nature of Cr and Co complexes, dramatically different from that of the extremely labile lanthanide solvento ions, facilitates the isolation of isomeric species and was crucial in enabling Alfred Werner to formulate the fundamental tenets of coordination chemistry. For simple lanthanide ion complexes, their lability and the lack of a marked sensitivity of their visually observed colors to the nature of the coordination sphere renders Wernerian procedures inapplicable, such that the establishment of high and variable coordination numbers as a characteristic of lanthanide ions has depended largely on modem spectroscopic and crystallographic measurements. 

The luminescence of the lanthanide ions spreads from the UV spectral range up to the NIR, and many lanthanide ions have unique spectral characteristics in the visible region of the spectrum, which also give them distinctive luminescent colors. A lot of applications take advantage of those characteristic emissions for color reproduction and lighting. Phosphors, nanomaterials made of lanthanide complexes or enclosing lanthanide compounds, as well as LEDs based on lanthanide complexes are extensively investigated. 

Several lanthanide ions have a characteristic color in water solutions, as shown in Table 17.14. The color for an element ion with n f-electrons is very similar to those element ions that have (14 - n) electrons. In the table the colors of powdered common oxides are shown. 

A hot aqueous solution of lanthanide sulfate hydrate, Ln2(S04)3- H20 (where Ln = La, Ce, Pr, Nd, or Sm), taken in H2SO4 is mixed with (N2H5)2S04 or N2H6SO4. The resulting solution when left to stand in air affords the respective hydrazinium rare earth metal sulfate [19]. Small crystals suitable for X-ray studies are obtained in a few days. They exhibit the characteristic color of the lanthanide ions ... 

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 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 zinc reduction of Eu + to Eu +, followed by its precipitation as the sulfate, is a traditional step in the separation of europium from other lanthanides. In general, the solubilities of the inorganic compounds of the Ln + ions resemble those of the corresponding compounds of the alkaline earth metals (insoluble sulfate, carbonate, hydroxide, oxalate). Both europium and the Sm + and Yb + ions can also be prepared by other methods (e.g. electrolysis), although these solutions of the latter two metals tend to be short-lived and oxygen-sensitive in particular. Eu + is the only divalent aqua ion with any real stability in solution. Several divalent lanthanides can, however, be stabilized by the use of nonaqueous solvents such as HMPA and THE, in which they have characteristic colors, quite distinct from those for the isoelectronic trivalent ions on account of the decreased term separations. 

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