Absorption and emission spectroscopy represent two complementary analytical methodologies. In absorption spectroscopy, a continuous broad-spectrum light beam illuminates the sample, and the instrument measures which wavelengths the material attenuates as photons promote electrons to excited states.
Emission spectroscopy (including fluorescence and photoluminescence), by contrast, first excites the specimen with a laser or narrow light source. As the excited electrons relax back to their ground thermodynamic states, they re-emit photons at longer, characteristic wavelengths against a zero-background optical field.
In gemstone analysis, combining both methods is paramount: absorption identifies deep bulk chemical constituents and nitrogen aggregates, while photoluminescence detects minute sub-ppb impurity centers such as silicon vacancies (SiV) in CVD diamonds.