White sapphire

Spinel is a colorless magnesium aluminate (MgAl204) of cubic structure. It is hard and durable, but, like white sapphire, it is not a good diamond substitute because it has a low refractive index and lacks brilliance. However, it is readily doped to produce other gems of various colors. Artificial ruby, for example, is often natural red spinel, and most synthetic blue sapphires on the market are actually blue spinel. 

Is this stone really diamond not cubic zirconia (CZ), white sapphire, or even moissonite ... 

The flame fusion technique (see Figure 7.20b) was originally devised in 1904 by Verneuil for the manufacture of artificial gemstones, such as corundum (white sapphire) and ruby. This method is now used for the mass production of jewels for watches and scientific instruments. A trickle of fine alumina powder plus traces of colouring oxides is fed at a controlled rate into an oxyhydrogen flame. Fusion occurs and the molten droplets fall on to a ceramic collecting rod. A seed crystal cemented to the rod is fused in the flame and the rod is lowered at a rate that allows the top of the growing crystal (known as a boule) to remain just molten. Renewed interest has recently been shown in this method for the production of rubies for lasers. 

Aluminum oxide, or alumina, ciystalUzes in the corundum stracture (mineralogical term) to form sapphire monociystals. We are referring here to white sapphire, like the one used for the manufacture of scratchproof glasses for watches, whereas in gemmology sapphire is the blue sapphire, which is alumina with a little Ti" mby being alumina colored in red by Cr +. This is the alpha variety (Al203-a), which is the stable variety, but we will see that the preparation of alumina involves various metastable varieties hydrated aluminas and transition aluminas. 

Corundum, when pure, is also known as the gemstone white sapphire. Certain other gemstones consist of corundum with small amounts of transition metal ions as impurities Cr in ruby and Fe and Ti in blue sapphire, for example. Artificial gemstones are made by fusing corundum with carefully controlled amounts of other oxides. 

Material like sapphire, which is a uniaxial crystal, does not show nonlinear fluorescence, and direct visualization of filaments is, consequently, not an option. However, the effect of rotation of plane polarization can also be probed in such materials by monitoring the spatial size of the white light disc, and of the spectrum of the super continuum that is produced. Figure 5.3 depicts some typical results obtained with 3 mm long sapphire crystals. The extent of the supercontinuum spectrum is seen to vary as a function of polarization angle. The supercontinuum spectrum has two components [39] symmetric broadening about the incident wavelength that is essentially ascribable to... 

Fig. 5.3. Top panel Polarization-dependent supercontinuum spectra obtained in sapphire. The corresponding variation in the diameter of the white light central spot as a function of incident polarization angle is shown in the lower panel...

Beneath the Chamber of Starry Wisdom is the Hall of the Desirous Quest (Chesed). It has an amethyst altar and four pillars, two of lapis and two of crystal. The walls are of translucent sapphire, the roof a white dome. The eastern throne is of gray granite the floor squares are white and blue within it are hung tapestries of the tarot Keys, V, VIII, IX, and X. 

The Sephiroth of the Tree change into the Queen Scale of Briah and, simultaneously, you see that the field of the phoenix shield that hangs over the door to the chapel, is changed from white to azure. And within the chapel, the royal orb, cushioned upon the altar, is now formed of precious blue sapphire. 

Very recently, white light continuum pulses of duration ca. 200 fsec, pulse energy ca. 1 / J, and peak wavelength of ca. 780 nm have been generated at repetition rates up to 250 kHz by commercially available Ti sapphire regenerative amplified laser systems. Such systems are very expensive, but the expected easier use, as compared with homemade systems, should open up new research applications for time-resolved fluorescence and absorption techniques in the near-IR. 

P. F. Curley, A. I. Ferguson, J.G. White and W. B. Amos, Application of a femtosecond self-sustaining mode-locked Ti sapphire laser to the field of laser scanning confocal microscopy, Opt. Quant. Elec. 24, 851-859 (1992). 

An example of high-contrast resonant imaging of tissue structures with this source is shown in Figure 5.4a. Here, the white adipose tissue of a mouse omentum majus is imaged at a depth of -10 pm from the surface at a Raman shift of 2850 cm ( ump = 924 nm A tokes = 1254 nm). In contrast, for the same Raman shift, two synchronized Ti sapphire lasers (Potma et al. 2002) would typically have pump and Stokes wavelengths of -710 nm and -890 nm, respectively, and are much more strongly scattered in turbid tissue. 

However, such comparison is a meaningless exercise. A comparison of silicon, sapphire, GaAs, or other established materials, rather than other SiC growth techniques, should occur instead. The blue and white LEDs can, for instance, be made on either sapphire or SiC substrates. From a performance point of view, there appear to be advantages with the SiC substrate but the substrate cost is lower on sapphire, therefore making it the most-used substrate. Granted, once larger substrates of SiC are made available, it is doubtful that the LED cost will be lower on sapphire. 

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... 

Transient spectra of solvated indole are measured in a 120 Jim liquid jet with a crosscorrelation of 80 fs by means of a white light continuum (450 - 740 nm) generated in a sapphire disc. The molecules are excited at 270 nm with pump pulses generated by frequency doubling the output of a noncollinearly phase matched optical parametric amplifier [2], Due to the short pump pulses there is a small yet finite probability for two-photon ionization in pure solvents. This allows us to study the spectral properties of the generated solvated electrons by measurements in pure solvents. The transient spectra of the indole solution are corrected for these solvent contributions. 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

Several crystal structures of the oxide are known. The most common one is a-Al203 which is made by the calcination of A1205.3H20. Natural corundum is found as semi-translucent masses with a white or greyish colour. It resembles quartz. Chemically seen, corundum is related to the much more beautiful sapphire and ruby. These have the same formula, A1203, but in their cases impurities result in the colour. 

Fig. 1. Schematic diagram ot high-pressure apparatus tor enzyme activity tests. A, C02 cylinder B, syringe pump C, equilibrium cell D, sapphire windows E, magnetic stirrer F, white light source G, pressure transducer H, ball valve I, micrometering valve J, relief valve.

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