ASS #6- Key Terms & Concepts PDF

ASS #6: Key Terms Absorption Spectrum—A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope, or a linear graph recorded by a spectrometer. Band Gap—Energy difference between the valence band and the conduction band. Color Center—A defect that...

ASS #6: Key Terms Absorption Spectrum—A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope, or a linear graph recorded by a spectrometer. Band Gap—Energy difference between the valence band and the conduction band. Color Center—A defect that can influence an object’s absorption of visible light to cause its color. Colored Lamellae—Closely spaced grain lines where color concentrates. Electromagnetic Spectrum—The range of wavelengths of radiant energy extending from high energy to low energy, including visible light. Fluorescence—Emission of visible light during stimulation by UV or X-ray radiation. Luminescence—Emission of visible light by a material when it is exposed to a radiation source. Phosphorescence—Continued emission of visible light after UV or X-ray stimulation stops. Selective Absorption—The process by which a material absorbs some components of visible light and transmits others. Transmission—The process by which light not absorbed by a material returns to the observer. Visible Spectrum—The range of wavelengths of visible light from 400 nm (violet) to 700 nm (red). Wavelength—The distance between two adjacent high or low points of a wave. Key Concepts: Light is a form of radiant energy that travels in waves. Light of shorter wavelengths has higher energy than light of longer wavelengths. Visible light is a small portion of the electromagnetic spectrum. White light is a combination of spectral colors. Diamond color is primarily caused by defects in the crystal lattice. The spectroscope and spectrometer can help gemologists see a diamond’s absorption spectrum. Interaction of electrons with visible light causes most selective absorption–related gem colors. Diamonds without color centers are colorless due to the lack of visible light absorption. Color-causing defects work as energy “steps” within a diamond’s band gap to ease the electron transitions “fueled” by visible light absorption. Nitrogen-related defects are the most common causes of yellow color in diamonds. The most common cause of green color in diamonds is radiation. Naturally irradiated diamonds usually contain areas of green or brown radiation damage on their surfaces or penetrating into the stones. Boron impurities are responsible for blue color in type llb diamonds. The GR1 defect, caused by radiation, can create blue color in diamonds with low nitrogen concentrations. Deformation-caused selective absorption is the main cause of color in pink-to-red diamonds. Inclusions are the main causes of black, gray, and white colors in diamond. The energy level of luminescence is lower than that of the radiation source. Luminescence is an efficient visual test for diamond identification.