The active layer in a PSP plate is typically composed of phosphors from which family?

• A. Barium fluorohalide
• B. Rare-earth oxides
• C. Sodium halide
• D. Calcium tungstate

Answer: (A)

The active layer in a PSP plate uses a storage phosphor from the barium fluorohalide family, typically BaFBr:Eu2+ and BaFCl:Eu2+. When X-rays expose the plate, electrons are trapped in the europium-doped barium fluorohalide lattice, storing the latent image. Later, a red laser in the reader stimulates these traps and releases the stored energy as light, producing the image. This family is favored because the heavy elements provide good X-ray absorption and the europium dopant creates efficient traps with bright, well-defined emission upon stimulation, enabling high resolution and good detective performance. Other options are not used for this purpose: they either don’t form effective storage phosphors for PSP readout or are scintillators that emit light immediately rather than store it for later retrieval.