What is the photocathode made of?

The photocathode is a crucial component in various imaging systems, including image intensifiers used in fluoroscopy. It is designed to convert incoming light photons into electrons through the photoelectric effect. The materials used for photocathodes are specifically chosen for their photoemissive properties, allowing them to efficiently emit electrons when exposed to light.

The correct option highlights a combination of cesium and antimony, which are known to form a photoemissive compound. This specific combination results in a highly effective photocathode with good sensitivity to a range of light wavelengths, especially in the visible spectrum. This characteristic is essential for optimizing image quality in fluoroscopic applications where low light conditions may be present.

In contrast, the other options listed do not possess the necessary photoemissive properties or efficiency required for effective photocathodes. The materials cited in those options, while they may have applications in other areas, do not meet the specific criteria for creating a high-performing photocathode in imaging technologies.