A cathode ray tube phosphor has the composition x(ZnO)Y 2 Si0 7 , 1≧x≧0.42 doped with at least one emitting ion. The emitting ion may be Mn 4+ or Eu 3+ to give a red emission; Mn 2+ orTb 3+ to give a blue emission. The phosphor (5) is coated on the inner face plate of a cathode ray tube (1). The coating may have different areas coated with different emitting ion to give a colour television tube. The tube may be used as part of an aircraft head up display.