Monday, 07 May 2018 17:47


Luminous materials were known in the times of the Greeks and Romans. Aristotle mentions the sea, meat and some fungi (rotting wood). 

Then in the 17th century phosphorescent substances were discovered “the marvellous light-absorbing and light-emitting luminous minerals”. 

Casciorolo (1602-4) working in Bologna, discovered that barium sulphide when put between red-hot coals became luminous.

In 1674 Christoph Adolph Balduin (1632–1682) first produced calcium nitrate. Everything in a glass vessel after being highly heated and dried up was found to be luminous. Named it ‘Balduin’s phosphorus’ (‘phosphorus’ means carrier of light).

Since these minerals were stimulated to phosphorescence by a preceding exposure to radiation or sunlight and emitted a fairly bright light, they were looked upon as a magnet or a kind of sponge which could suck up light and give it out again.

Dr. Brand in 1674-5 attempted to distil human urine and in this way discovered phosphorus. 

In 1801 JW Ritter (1776-1810) discovered ultraviolet rays. When he covered paper with damp freshly prepared silver chloride and let the solar spectrum act on it in a darkroom he saw that the action began first beyond the ultraviolet and only then proceeded towards the violet.

He also noted that silver chloride paper already exposed to diffused daylight that had turned slightly dark became darker in the violet end of the spectrum but lighter in the red end. This observation first pointed to the antagonism of the chemical effect of violet and red light.

Becquerel (1820-91) showed that nearly all fluorescent substances are phosphorescent although in some cases the phosphorescence may continue for only a fraction of a second. 

Phosphors are used on TV screens and monitors that used cathode ray tubes (CRT). Green phosphors are used with Oscilloscopes and for Scanning Electron Microscopy.

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