OPTICAL BRIGHTENERS, fluorescence bleaching substances. Optical Brighteners (OBs) – are colorless or slightly colored organic compositions able to absorb UV part of sunlight (300-400 nm) and transform absorbed energy to visible light mostly in blue or violet spectrum (400-500 nm). Maximal florescence effect lies in the range of 415-466 nm. OBs should:
- Perform florescence with high quantum output;
- Radiate in the same spectrum, which is usually absorbed by contamination of the target material;
- Disperse itself homogeneously without aggregating to bigger molecular particles which can decrease bleaching effect.
The bleaching effect of OBs is based on the ability to compensate the lack of blue spectrum in the light reflected by target material (here lies the crucial difference from chemical Brighteners, like Cl2 or H2O2). Unlike adding blue color with Ultramarine, when yellowish color is decreased with red-yellow light absorption (but the brightness is decreased also), while using OBs the reflection of blue-violet light grows thanks to fluorescence. High whiteness and brightness is reached with adding OBs in quantity 0,001-0,1% of target material mass and has best performance under sunlight or UV radiation.