Confusion of terminology
In the literature luminescence, phosphorescence and fluorescence are often used interchangeably which can lead to confusion.
Fluorescence/Luminescence
The emission of light from a substance when exposed to light.
Fluorescence and luminescence are generally used to describe the effect of excitation caused by ultraviolet and blue light. Luminescence is usually associated with infrared luminescence, which is stimulated by blue/green light.
In fluorescence and luminescence as soon as the light source is turned off the emission of light stops, ending within about 10-8 seconds after extinction if not faster. Substances that fluoresce on their own are said to ‘Autofluorescence’ in many uses of fluorescence fluorescent markers are used to make non-fluorescent things fluoresce.
Fluorescence can also include the action of blue or blue-green light on chemicals. One in common use is fluorescein which fluoresces green/yellow and is used in contact lens assessment and diagnostically in eye conditions.
Phosphorescence
The emission of light from a substance when exposed to light which continues after the light source is turned off.
In phosphorescence:
- Light is absorbed by the material
- Light is released over a period of time
Barium sulphide, calcium sulphide or strontium sulphide. A card painted with calcium sulphide well known as luminous paint - fluoresces greenish/blue. In a darkroom it will continue to glow for a time depending on the length of exposure and intensity of the exciting radiation.
Bioluminescence
Light is created by physiological or chemical means within a biological organism for example the Angler fish, glowworms and fireflies.
Chemiluminescence
Light created by the mixing of two chemicals which react and energy is released in the form of light.
Triboluminescence
Emission of light brought about by grinding certain crystalline substances. Sugar when crushed luminescent sparkles are visible.
Incandescence
Emission of light by a material solely because it is heated which occurs when thermal energy is transformed into light energy. For example carbon particle in candle flame, liquid molten metal, emits a continuous spectrum of colour.