Cathode ray tube (crt):

Displays of this type, which are based on the electron beam scanning technique, have been used in aircraft for many years.  They were first used to display weather radar information and have continued to be an essential part of the "Avionics Fit" in today's modern aircraft.

The CRT is a thermionic device, i.e. one in which electrons are liberated as a result of heat energy.  It consists of an evacuated glass envelope inside which are positioned an "Electron Gun", "Beam-Focusing" and "Beam-Deflection" system.  The inside surface of the screen is coated with a crystalline solid material known as a phosphor.

Figure: shows a cross-section of a CRT.