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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).
|Fluorescence||produced by exposure to invisible radiations, such as ultra-violet light or x-rays.|
|Phosphorescence||the afterglow of fluorescence when the stimulating radiations have been shut off.|
|Thermoluminescence||a secondary light generated by certain substances when heated with invisible infra-red rays.|
|Triboluminescence||the phenomenon exhibited by certain minerals when they are rubbed or scratched of exhibiting luminosity.|
|Cathodoluminescence||fluorescent effect displayed by some materials when they are bombarded with a been of electrons|
|Electroluminescence||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.
|Longwave||380 to 300 nanometres|
|Shortwave||300 to 200 nanometres|
|Paste (Glass)||Inert||Bright pale blue or green|
|Natural Blue Sapphire||Inert (due to Iron)||Inert|
|Synthetic Blue Sapphire||Inert||Greenish-blue due to Titanium|
|Natural Blue Spinel||Inert||Inert|
|Synthetic Blue Spinel||Red (due to cobalt)||Bluish-white|
|Cubic Zirconia||Mustard yellow||Less pronounced|
|Natural Purple Sapphire||Inert||Inert|
|Synthetic Purple Sapphire||Red||Bluish-white|
|Synthetic Ruby||More intense red||More intense red|
|Natural Emerald||Green to Red||Inert|
|Synthetic Emerald||Strong red glow||Strong red|
|Diamond||Sky-blue, blue, green to yellow. Stones that fluoresce blue have a yellow afterglow||less pronounced|
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.