Which sequence correctly describes the chain of events from x-ray exposure to digital signal in PSP?

• A. X-rays hit PSP; europium electrons absorb energy; halogen vacancies capture the excited electrons; latent image forms; red light stimulates release; green light emitted; voltage; digital signal
• B. X-rays strike PSP; energy is stored as heat and read later as digital data
• C. X-rays hit PSP; europium electrons absorb energy; electrons move to halogen vacancies (F centers); latent image is formed by metastable electrons trapped in F centers; red light stimulates release, green light emitted; green light is converted into voltage; voltage becomes a digital signal
• D. X-rays hit PSP; energy is directly converted to a digital signal without intermediate steps

Answer: (C)

The key idea is that PSP imaging stores x-ray energy as trapped electrons in the phosphor and then releases that energy as light that a detector converts into a digital signal. After x-ray exposure, europium-doped halide crystals trap metastable electrons at F-centers (halogen vacancies), forming a latent image. When a red laser scans the plate, those trapped electrons are released, recombine, and emit green light. The emitted green light is then detected and converted into an electrical signal, which is digitized to produce the digital image. This sequence—from energy absorption and trapping to red-stimulated release, green light emission, and optical-to-electrical conversion—is precisely the process described.