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Luminescence is emission of light by certain materials when they are relatively cool. It is in contrast to light emitted from incandescent bodies, such as burning wood or coal, molten iron, and wire heated by an electric current. Luminescence may be seen in neon and fluorescent lamps; television, radar, organic substances, certain pigments used in outdoor advertising; and also natural electrical phenomena such as lightning. In all these phenomena, light emission does not result from the material being above room temperature, and so luminescence is often called cold light.

Although lightning and the dim light of glowworms and of fungi have always been known to mankind, the first investigations (1603) of luminescence began with a synthetic material, when Vincenzo Cascariolo, an alchemist in Bologna, Italy, heated a mixture of barium sulfate and coal; the powder obtained after cooling exhibited a bluish glow at night, and Cascariolo observed that this glow could be restored by exposure of the powder to sunlight. The name lapis solaris, or “sunstone,” was given to the material because alchemists at first hoped it would transform metals into gold, the symbol for gold being the Sun. The pronounced afterglow aroused the interest of many learned men of that period, who gave the material other names, including phosphorus, meaning“light bearer,” which thereafter was applied to any material that glowed in the dark.

One of the first scientific investigations of the luminescence was performed in 1672 by Robert Boyle, an English scientist.

Today, the name phosphorus is used for the chemical element only, whereas certain microcrystalline luminescent materials are called phosphors. Cascariolo’s phosphor evidently was a barium sulfide; the first commercially available phosphor (1870) was “Balmain’s paint,” a calcium sulfide preparation. In 1866 the first stable zinc sulfide phosphor was described. It is one of the most important phosphors in modern technology.