Stokes shift

physics

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

The Stokes shift refers to the difference in wavelength between the light absorbed and the light emitted by a substance during processes like fluorescence or the Raman effect.1

When a molecule absorbs a photon, it moves to an excited state. If it then emits a photon that doesn't have enough energy to return it to its original ground state, the emitted light will have a longer wavelength. This phenomenon, named after Sir George Gabriel Stokes, is a fundamental aspect of how certain materials interact with light. The relaxation of nuclei to their excited-state positions after electron excitation contributes to this shift, causing fluorescence to emit lower-energy light than was originally absorbed.12

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

2 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

Stokes lines
…absorbed light is called the Stokes shift.
Read More
…absorbed light is called the Stokes shift.
Read More

photochemical reaction
Consequences of photoexcitation
This relaxation, called the Stokes shift, is why fluorescence emits with a lower energy than the original absorption. It is notable that this relaxation occurs within a single electronic state and so applies when both the absorption and fluorescence involve the S₁ and S₀ states.
Read More
This relaxation, called the Stokes shift, is why fluorescence emits with a lower energy than the original absorption. It is notable that this relaxation occurs within a single electronic state and so applies when both the absorption and fluorescence involve the S₁ and S₀ states.
Read More