Sapphire blue color

When a solution of niobic add in concentrated hydrochloric add (2 1) is boiled with tin for some time, a deep sapphire-blue coloration is obtained, which fades on standing and is regenerated by boiling. 

Some treatments are practiced so widely that untreated material is essentially unknown ia the jewelry trade. The heating of pale Fe-containing chalcedony to produce red-brown carnelian is one of these. Another example iavolves turquoise where the treated material is far superior ia color stabiUty. Such treatments have traditionally not been disclosed. Almost all blue sapphire on the market has been heat treated, but it is not possible to distinguish whether it was near-colorless comndum containing Fe and Ti before treatment, or whether it had already been blue and was only treated ia an attempt at marginal improvement. The irradiation of colorless topa2 to produce a blue color more iatense than any occurring naturally is, however, self-evident, and treatments used on diamond are always disclosed. 

Sapphyrins were discovered serendipitously by Woodward33 during the course of synthetic studies directed towards the total synthesis of vitamin B, 2. The sapphyrins were the first example of expanded porphyrins in the literature. Due to sapphyrin exhibiting a deep-blue color in the crystalline state and intense green in solution. Woodward coined the expression sapphyrin with reference to the deep-blue color of sapphire stones. 

Sapphire. —To produce a fine oriental blue color, one must employ very white strass, and very pure oxide of cobalt. This composition, put into a luted Hessian crucible, should remain thirty hours in the fire. Tho... 

Gem quality beryls are aquamarine (blue), emerald (green), and golden beryl. Likewise, amethyst b a violet-colored silica, and sapphire (blue) and ruby (red) are alumina. Yet pure beryl (Be,AI>Si lO ). alica (SiO ). and alumina (AI O>) are colorless. Explain... 

Color Dk blue crystals e Yel-orange prisms Sapphire-blue crystals ... 

Representative optical spectra of various sapphires are illustrated in fig. 4.16. It is apparent from the spectra of the natural blue sapphire (fig. 4.16b) that absorption minima in the violet-indigo and blue-green regions, which are located between sharp peaks at 25,680 cm-1 and 22,220 cm-1 and broad bands spanning 17,800 to 14,200 cm-1, are responsible for the blue coloration. Absorption at 17,800 to 14,200 cm-1 is less intense in spectra of natural yellow sapphire (fig. 4.16a see also fig. 3.21) containing negligible Ti. The spectra of synthetic Ti3+-doped A1203 (fig. 4.16c) show absorption maxima at... 

Thus far, we have only considered the colors responsible for doping a crystal with one type of metal ion. However, crystals such as blue sapphire contain two metal dopants that yield the desirable deep blue color due to charge-transfer effects. If two adjacent Al sites in alumina are replaced with Fe " " and Ti " ", an internal redox reaction may occur, where the iron is oxidized and the titanium is reduced (Eq. 14). 

The deep blue color or sapphire gems results from the addition of a few hundredths of one percent of iron and titanium impurities to alumina. The Fe2+ and Ti4+ ions substitute for aluminum in the sapphire, and when light of energy of 2.11 eV is shone on the sapphire, it is absorbed by the charge transfer reaction ... 

As a member of the corundum family of minerals, sapphire (the September birthstone) consists primarily of aluminum oxide, AI2O3. Small amounts of iron and titanium give it its rich dark blue color. Gem cutter Norman Maness carved a giant sapphire into the likeness of Abraham Lincoln. If this 2302-carat sapphire were pure aluminum oxide, how many moles of AI2O3 would it contain (There are exactly 5 carats per gram.)... 

The AA, one A bright and the other A shadowed, symbolises that half the work is visible and half is veiled. Sir Francis Bacon later entwined the two letters with hyacinth flowers, or the herb Asclepias acida, representing the golden flower of alchemy. This flower, though golden in nature, is the hyaeinthine color of blue or the sapphire blue of the hermaphrodite ... 

FIGURE 36.13 (a) Illustration of the combined effect of incorporation of Ti and Fe in sapphire. The distance between the dopant cations is 0.265nm. (b) The corresponding energy band diagram for the excitation showing how a gemstone with blue coloration is obtained by absorption. 

For sapphire blue, the color results from a charge transfer mechanism. Sapphire shares the corundum structure with ruby, but the impurities are now small amounts of both iron and titanium oxides. Both Fe " and Ti " take the place of AE" in the corundum structure. If they are present on adjacent sites, as shown in Figure 36.13, then an interaction between them becomes possible. In this configuration there is enough overlap of the orbitals of the two ions that it is possible for an electron to transfer from the Fe ion to the ion as follows ... 

Sapphire heated to modify or develop a blue color Yes Usually Yes... 

Description. Sapphire occurs in a wide range of colors such as blue, pink, padparadscha orange, yellow, green, purple, black. Color is due to trace impurities of FeG Fe , Ti, and yellow color centers. The most expensive color is an intense cornflower blue these are sometimes referred to as Kashmir sapphires having a highly saturated, slightly milky, violet blue color. Padparadscha is next in value, followed by pink, then orange, purple and yellow, respectively. Nowadays 400-500 tonnes of synthetic sapphire are produced by the Verneuil process each year. 

The main colored varieties are ruby (red) and sapphire (blue). The corresponding color centers may present in different quantitative and qualitative proportions with resulting varieties of colors (up to 2000 different tints). The main color center in ruby is impurity of Cr (up to 4 %). Ion Cr " generates two strong absorption bands in the visible part of the spectrum, which explain the red color. Different tints of red, which influence strongly on the commercial value, are connected with impu-... 

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