The fluorescence of organic dyes is associated with the individual molecules of the dyes, and in order for them to fluoresce efficiently, they must be molecularly dissolved and in fairly low concentrations from about 1 to 4%. In the pure solid state or in very concentrated solutions the dyes have almost no fluorescence and appear as dark or dirty red, yellow and green powders or solutions. The individual molecules of the dyes are so close together that they simply quench or reabsorb their own fluorescent light. Since the dyes are organic in nature it is necessary to have a medium or carrier in order to put them into solution, and to have a pigment it is necessary that this medium be a solid. The type of material which meets these requirements for the dyes is an organic resin, and daylight fluorescent pigments are actually transparent organic resin particles containing dyes in solution which are capable of fluorescing.
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