Luminescent materials

Luminescent inorganic materials (phosphors) have been in common use for several decades, those related to ZnS having been discovered in the mid-nineteenth century. Phosphors continue to be an important commodity, and there are efforts to improve the efficiency and colour of existing phosphors as well as to make new ones (Hill, 1983 Hagenmuller, 1983). Small quantities of impurities markedly affect the luminescence characteristics of phosphors for example one or two parts in 10 of copper dominates the luminescence of ZnS. 

Cathode ray tube phosphors with fast luminescence as well as persistent luminescence are needed in different situations. A variety of phosphors of the ZnS-CdS family are used for the purpose with Ag, Cu etc. as dopants. Other host lattices used are CaS, Zu2Si04, Y2O2S and Zn3(P04)2 typical dopants are Mn, Ce, Eu and Tb. 

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Schmuki P, Lockwood D J, Bsiesy A and Isaacs FI S (eds) 1997 Pits and Pores Formation, Properties, and Significance for Advanced Luminescent Materials Proc. vol 97-7 (Pennington, NJ Electrochemical Society)... 

Chemiluminescent Immunoassay. Chemiluminescence is the emission of visible light resulting from a chemical reaction. The majority of such reactions are oxidations, using oxygen or peroxides, and among the first chemicals studied for chemiluminescence were luminol (5-amino-2,3-dihydro-l,4-phthalazinedione [521-31-3]) and its derivatives (see Luminescent materials, chemiluminescence). Luminol or isoluminol can be directly linked to antibodies and used in a system with peroxidase to detect specific antigens. One of the first appHcations of this approach was for the detection of biotin (31). 

Nonradiative Decay. To have technical importance, a luminescent material should have a high efficiency for conversion of the excitation to visible light. Photoluminescent phosphors for use in fluorescent lamps usually have a quantum efficiency of greater than 0.75. AH the exciting quanta would be reemitted as visible light if there were no nonradiative losses. 

Chemiluminescent analyzers are based on the light (chemiluminescence) emitted in the gas-phase reaction of ozone with ethylene, which is measured with a photomultipHer tube. The resulting current is proportional to the ozone concentration (see Luminescent materials, chemiluminescence). 

Luminescent Pigments. Luminescence is the abihty of matter to emit light after it absorbs energy (see Luminescent materials). Materials that have luminescent properties are known as phosphors, or luminescent pigments. If the light emission ceases shortly after the excitation source is removed (<10 s), the process is fluorescence. The process with longer decay times is referred to as phosphorescence. 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

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