A storage phosphor is a type of phosphor material used in various imaging, radiation detection, and dosimetry technologies. When exposed to X-rays, gamma rays, or other forms of ionizing radiation, such material can store a portion of the absorbed energy. This stored energy can later or immediately be released as visible light when stimulated by another light source, typically a laser. The emitted light is then captured and used to create a digital image.
Radiation imaging is used widely in areas such as medical imaging, industrial radiography, and scientific research. For example, in Computed Radiography (CR), storage phosphor plates or sheets are used to capture and store X-ray images. These plates can then later release the images as light when scanned with a laser, producing a digital image. In Digital Radiography (DR), phosphor screens are also used to create images, but the images are immediately digitized using a direct digital capture system.
Storage Phosphor & Optically Stimulated Luminescence:
Storage phosphors and related single crystals are based on the phenomenon of optically stimulated luminescence (OSL). The OSL process in these optical materials can be triggered in 4 basic steps:
1. Energy Storage: when a storage phosphor is exposed to ionizing radiation, it can absorb and store energy in the form of trapped electrons within its crystal lattice.
2. Stimulation: when the sample is then exposed to a specific wavelength of light, usually from a laser or LED, this light energy stimulates the trapped electrons within the phosphor.
3. Luminescence: as the trapped electrons are released, they return to their normal state and emit light (luminescence). The intensity of this emitted light can then be measured using standard optical detectors.
4. Measurement: the amount of luminescence is proportional to the accumulated radiation dose. For a medical imaging plate, this translates into regions of bright and dark areas corresponding to the density of the body parts or objects blocking the original radiation source, such as X-rays.
A typical application of storage phosphor screens is in computed radiography employed by various medical instruments