What are the main characteristics of ultraviolet rays, which can make the negative film sensitive, sterilize and have fluorescent effect?

The main feature of ultraviolet ray is its strong chemical action, which is easy to make photographic film sensitive; (physiology) It is very powerful and can kill bacteria. Using the (fluorescence) effect of ultraviolet rays, anti-counterfeiting and photography can be carried out. Excessive ultraviolet rays are harmful to people, and the sun is an important source of natural ultraviolet rays. Most of the ultraviolet rays in the sun are absorbed by ozone in the upper atmosphere and cannot reach the ground.