Fluor Crown glass
Fluorine Crown Glass is referred to as FK glass. It belongs to low refractive index, low dispersion, colorless optical glass. It belongs to China's light crown glass (QK), and some countries also call it fluorine crown glass. But its composition is actually mostly borosilicate glass that does not contain fluorine or contains little fluorine. The ultra-low refractive index optical glass or ultra-light crown optical glass developed later belongs to fluoride glass and is called fluorine crown glass in China. Its optical constant is already in the lower left corner of the nd-v diagram. However, fluoride glass has poor chemical stability and is easy to glass devitrification. Adding a small amount of oxygen-containing compounds can be appropriately improved, such as NaPO3 or P2O5. Mainly used as a material for optical components in optical instruments.
By modifying the glass formula, the optical glass without lead, arsenic and cadmium and other radioactive elements is expressed by a prefix "H-" indicating its envioronment-friendly characteristics, for example: H-FK61.
