Highly refracting glasses

This soft, silver white metal reacts with air and water. The oxide is applied in optical glasses with high refractive indices (special lenses for powerful cameras and telescopes). Used for special effects in optoelectronics and electronics. Lanthanum exhibits catalytic properties. It is a component of flint and battery electrodes. Lanthanum boride (LaB6) is the superior electron-emitter for electron microscopes. Lanthanum is the first of the series of 14 lanthanides, also called the "rare-earth" metals, whose inner N shells are filled with electrons. They do not belong on the "red list" of endangered species they are neither rare nor threatened with depletion. China is particularly rich in lanthanide ores. 

In Fig. 9.1, the situation is explained for a light beam traveling through a high refractive index medium (i.e., glass or immersion... 

Germanium dioxide has high refractive index and infrared transmission, for which it is used in industrial glasses. It also is used in preparation of high purity grade germanium. 

Highly pure lanthanum oxide is used to make optical glass of high refractive index for camera lenses. It also is used to make glass fibers. The oxide also is used to improve thermal and electrical properties of barium and strontium titanates. Other applications are in glass polishes carbon arc electrodes fluorescent type phosphors and as a diluent for nuclear fuels. In such apph-cations, lanthinum oxide is usually combined with other rare earth oxides. 

Tantalum pentoxide is used in making high refractive index optical glass as a dielectric film on tantalum for its use as a capacitor component and rectifier and for preparing tantalum metal, its carbide, and many other tantalum compounds. 

The most important range for inorganio chemicals is between 1 40 and 1 70. But there are some substances, such as certain oxides and sulphides, whose indices lie well above this range, or even well above 2 0. Media which are liquid at room temperature and have such high refractive indices are not available, but certain mixtures of substances which solidify to glasses may be used. A little of the medium is melted on a microscope slide, the substance under examination is dusted into the melt, a cover-glass is pressed on, and the slide is then allowed to cool. Substances which have been used in this way are mixtures of piperine with arsenic and antimony tri-iodides (for indices 1 7-2 1), mixtures of sulphur and selenium (2-0-2-7)—for details, see Larsen and Berman (1934)—and mixtures of the halides of thallium (Barth, 1929). 

Towards light, carbon disulphide possesses high refractive and dispersive powers, and in these properties is exceeded only by methylene iodide, bromonaphthalene and phenyl mustard oil. On this account it is used for filling hollow glass prisms for the production of spectra.4... 

A flexible optical fiber has a high-refractive-index, transparent core enclosed in a lower-refractive-index, transparent cladding (Figure 20-18a). The cladding is enclosed in a protective plastic jacket. The core and the coating can be made from glass or polymer. 

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