What happens when x-rays hit PSP?

• A. The plate emits visible light immediately
• B. Europium electrons absorb energy
• C. Halogen vacancies are created
• D. The plate heats up without emitting light

Answer: (B)

When x-rays hit a photostimulable phosphor plate, the energy is captured by the europium-doped phosphor and creates electron traps in the lattice. The europium dopant helps form metastable trap states that hold the excited charge so the image can be stored. The trapped energy isn’t emitted as light immediately; instead, it waits until the plate is scanned with a visible-light laser. The laser supplies just enough energy to release the trapped electrons, and as they return to their ground state they emit light that the scanner detects. This is why the option describing europium electrons absorbing energy is the best match—it names the dopant that creates the energy traps and stores the signal. The other choices don’t describe the stored-energy, trap-based mechanism or the readout which produces light only during stimulation.