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The effect noticed in some substances of giving out visible light when they are rubbed or scratched (Triboluminescence) or when they are irradiated with invisible electro-magnetic radiations (Fluorescence, Phosphorescence or Thermoluminescence).
|produced by exposure to invisible radiations, such as ultra-violet light or x-rays.
|the afterglow of fluorescence when the stimulating radiations have been shut off.
|a secondary light generated by certain substances when heated with invisible infra-red rays.
|the phenomenon exhibited by certain minerals when they are rubbed or scratched of exhibiting luminosity.
|fluorescent effect displayed by some materials when they are bombarded with a been of electrons
|form of luminescence produced by passing an electric current through them. Natural blue diamonds can be separated from artificially coloured blue diamonds using this technique since the former are semi-conductors while the latter are not.
Two methods used in Gemmology to produce luminescence are:
The invisible rays, in the wavelength beyond the visible violet, having a range of between 100 and 380 nanometres.
|380 to 300 nanometres
|300 to 200 nanometres
|Bright pale blue or green
|Natural Blue Sapphire
|Inert (due to Iron)
|Synthetic Blue Sapphire
|Greenish-blue due to Titanium
|Natural Blue Spinel
|Synthetic Blue Spinel
|Red (due to cobalt)
|Natural Purple Sapphire
|Synthetic Purple Sapphire
|More intense red
|More intense red
|Green to Red
|Strong red glow
|Sky-blue, blue, green to yellow. Stones that fluoresce blue have a yellow afterglow
Electro-magnetic radiations of extremely short wavelengths falling between the ultra-violet and gamma rays of the electro-magnetic spectrum. Effects seen under X-rays are less variable than those under U.V light and are therefore considered more conclusive.
Used to separate awkward Synthetic Rubies from Natural Rubies. Most Synthetic Rubies phosphoresce under X-Rays while Naturals do not.