Atomic fluorescence spectroscopy (AFS) is an analytical technique that involves the electronic transitions of atoms in a flame, furnace, or plasma being excited by electromagnetic (EM) radiation. When these atoms absorb energy, they become excited and subsequently release energy as they return to their original state. This emitted light, or "fluorescence," is observed at a right angle to the incident beam. Both absorption and emission processes transpire at distinct wavelengths, which are characteristic of the specific atomic species present. AFS is particularly useful for determining mercury (Hg) and other elements that form volatile hydrides, such as arsenic (As) and selenium (Se).

The instrumentation required for atomic fluorescence measurements includes a high-intensity light source, an atomizer, a wavelength selector, and a detector. While a continuum source would be desirable, it is rarely used due to its low power output. Instead, pulsed hollow-cathode lamps, electrodeless-discharge lamps, xenon or mercury arc lamps, and lasers serve as potential light sources.

The fluorescence signal intensity is proportional to the target element's concentration and irradiation intensity, making high-intensity sources and minimal interfering radiation essential. Various chemicals, such as releasing and protective agents, can be introduced into the matrix to minimize chemical and spectral interferences that arise during atomization.