Britannica Sources used in this answer

How does the wavelength of emitted light compare with the wavelength of exciting light in photoluminescence?

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

energy levels of a luminescent centre — luminescence Figure 1: Energy levels of a luminescent centre (see text).

In photoluminescence, the wavelength of the emitted light is generally equal to or longer than that of the exciting light. This occurs because a portion of the absorbed energy is typically transformed into nonradiating vibrational energy within the atoms or ions of the substance.1

When the emitted light has a longer wavelength—and thus lower energy—than the incident radiation, the phenomenon is associated with Stokes lines. The difference between the wavelengths of the absorbed and emitted light is known as the Stokes shift.2

In rare instances, such as when intense laser irradiation is used or when sufficient thermal energy contributes to the excitation process, the emitted light can have a shorter wavelength than the exciting light; this is referred to as anti-Stokes radiation.12