Pigments luminescent

Luminescent pigments are solid fine particulate (1 to 5 pm) luminescent materials, which reemit absorbed energy as light at lower energy than the energy absorbed (mainly in the visible spectral region) either almost simultaneously with (fluorescence), or subsequent to (phosphorescence) 

Luminescent pigments fine particulate activated and sensitized solids, producing luminescence upon excitation 

Activators (e.g. transition metal and rare earth ions) which act as luminescent centers optionally with sensitizers (e.g. Pb2+, Ce- , Eu +, Tb- +) are incorporated in 

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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. 

Zinc and calcium siUcates, and calcium tungstate doped with activators such an Mn, Pb, Sn, and Eu are just a few examples of a large number of known ionicaHy bonded luminescent pigments. HaUde phosphates of the general formula 3Ca(P0 2 CaX2, where X = F or Cl, and Sb " and are... 

CdS colorants find use in plastics, paints, soaps, mbber, paper, glass, printing inks, ceramic gla2es, textiles, and fireworks. Luminescent pigments based on CdS—ZnS are also produced. Pigments based on CdS sell for 35—60/kg. The redder materials are more expensive. 

This chapter deals with pigments that produce special effects magnetic pigments (Section 5.1), anticorrosive pigments (Section 5.2), luster pigments (Section 5.3), transparent pigments (Section 5.4), and luminescent pigments (Section 5.5). 

Cathode-ray tubes have a very large number of applications which require varying phosphor qualities. Table 58 lists the most important cathode-ray luminescent pigments. 

Inorganic luminescent pigments with long afterglows have long been used to make danger areas, escape routes, and switches visible. 

The following basic rules should be observed in processing luminescent pigments ... 

Natural teeth exhibit blue-white fluorescence in the long-wavelength UV [5.435]-[5.437]. Luminescent pigments are used to imitate this phenomena in artificial teeth. They are added to the ceramic paste at a concentration of 0.3-0.5 wt%. Yttrium silicates doped with cerium, terbium, and manganese give the best results [5.438]. The excitation maximum of these phosphors is in the range 325-370 nm. The fluorescence color of the teeth can be varied by changing the concentration of activators. 

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