Britannica
Sources used in this answer
Under what conditions can emitted luminescent light have a shorter wavelength than the exciting light?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
luminescence
Figure 1: Energy levels of a luminescent centre (see text).
In general, the wavelength of emitted luminescent light is equal to or longer than that of the exciting light, as some energy is typically lost to nonradiating vibrational energy of atoms or ions.1
However, emitted light can have a shorter wavelength than the exciting light—a phenomenon known as anti-Stokes radiation—under specific conditions:
- Thermal Energy: When atoms or molecules are already in an excited state due to high temperature, the emitted photon can combine the energy from the exciting radiation with the material's pre-existing thermal energy. This results in an emitted photon with higher energy (and thus a shorter wavelength) than the absorbed photon.12
- Intense Irradiation: In rare instances, such as when using intense laser beams, the interaction can lead to the emission of shorter-wavelength light.1
These emissions are referred to as anti-Stokes lines in the context of fluorescence and the Raman effect.2