Germanium is a Block P, Group 14, Period 4 element. The electronic configuration is [Ar] 3d¹⁰ 4s² 4p². In its elemental form germanium's CAS number is 7440-56-4. The germanium atom has a radius of 122.5.pm and it's Van der Waals radius is 200.pm. Germanium is a very important semiconductor. Zone-refining techniques have led to production of crystalline germanium for semiconductor use with extremely high purities. When germanium is doped with arsenic, gallium, or other elements, it is used as a transistor element in thousands of electronic applications. The most common use of germanium is as a semiconductor. Germanium is also finding many other applications including use as an alloying agent, as a phosphor in fluorescent lamps, and as a catalyst. Germanium and germanium oxide are transparent to the infrared and are used in infrared spectroscopes and other optical equipment, including extremely sensitive infrared detectors. The high refractive index and dispersion properties of its oxide's have made germanium useful as a component of wide-angle camera lenses and microscope objectives. The field of organo-germanium chemistry is becoming increasingly important.