Fluorescence Intensity and Analyte Concentration:

As you have learnt so far, there are two major processes includes in fluorescence emissions that are given below.

i) Absorption of radiation to generate excited atoms

ii) De-excitation of excited atoms by emission of radiation

You know that according to Beer's law, while a radiation of intensity P₀ is passed through an analyte of concentration c mol dm^-3 taken in a cell of thickness b cm,  an intensity of transmitted radiation (P) by an analyte is given by Lambert-Beer's law,

viz., P = P₀ e ^-εcb

Amount of light absorbed, P_abs  = P₀  - P = P₀ (1 - e^-εcb )

The intensit y of fluorescence, Pf, is proportional to the quantity of radiation energy absorbed.

P_f ∝ P_abs   = P_abs  φ

P_f = P₀ (1 - e^-εcb) φ

where, P_f  =  Intensity of fluorescence (total),

P_abs  = quantity of radiant energy absorbed,

φ  = fraction of excited atoms that undergo fluorescence when εcb is small.

P_f  = P₀   2.303εcb ×φ

Therefore, the fluorescence intensity is straight proportional to its concentration. Within quantitative AFS, the instrument is commonly standardised through a calibration curve.