Photostimulable phosphor plate

Also known as an image plate, a photostimulable phosphor (PSP) plate can be used record a two-dimensional image of the intensity short-wavelength (typically, X-ray) electromagnetic radiation.

Creating an image requires illuminating the plate twice: the first exposure, to the radiation of interest, "writes" the image, and a later, second illumination (typically by a visible-wavelength laser) "reads" the image.

Basic Explanation
After the initial exposure, excited electrons in the phosphor material remain 'trapped' in 'colour centres' in the crystal lattice until stimulated by the second illumination. The light given off during the second illumination can be collected (often by a photomultiplier tube), enabling the resulting signal to be converted into a digital image.

This process is also known as Photostimulable Luminescence (PSL).

Unlike film, a PSP plate can be reused: plates can be "erased," by exposing the plate to room-intensity white light.

History
Image plates were pioneered for commercial use by Fuji in the 1980s.

Medical X-ray Imaging
In modern hospitals, a PSP plate is used for X-ray imaging in place of the photographic plate, in a process called computed radiography. The PSP plate can be used over and over again.

X-ray Diffraction Studies
Image plate detectors have been used in numerous crystallography studies.