Image plates are two-dimensional detectors.
When exposed to neutrons, colour centres are created inside the phosphor in quantity proportional to the neutron dose. As in photographic films, these Colour centres makes a latent image. A red laser spot that releases the colour centres reads this latent image. Blue light is then emitted in a quantity proportional to the number of colour centres . While the plate is scanned, the intensity of the blue light is recorded as a function of the laser spot position, making then an intensity map of the latent image.