Photomultiplier tubes were used is earlier forms of the fax machine, photocopiers and drum scanners. The photomultiplier tube was for scanning the document.

There is a website called HAMAMATSU (yes, the website shows the name in all capital letters), that has an article on what a photomultiplier does, complete with a diagram.

A photomultiplier.

K. M. Hays has written:

'Study of solid state photomultiplier' -- subject(s): Aeronautical instruments

A PM tube doesn't operate in that wavelength.

A PM tube detects light which is generated from a scintillator. The scintillators are typically designed to scintillate as a result of a reaction with ionizing radiation.