5.4.3. Fluorescence Correction (F)
The correction for fluorescence is a function of the elements present, their concentrations, their values of Ec and mass absorption coefficients, and the take-off angle. The most important factors are the concentrations of fluorescing elements and elements fluoresced.
In general, the correction for fluorescence is the least important factor in the ZAF correction. The fluorescent yield (see Section 2.3.3) decreases with decreasing Z and is not important for the light elements, which dominate geological samples. The factor, Ff can be expressed as:
The fluorescent yield increases rapidly with increasing atomic number and Ff is negligible for K-lines of elements below atomic number 20. In silicates and oxides, absorption dominates and fluorescent enhancement is rarely greater than a few percent.