A phosphor layer is composed of tri-band phosphor particles bound together by
a
binder. A material as the main component of the binder is a mixture of (1) a compound
formed by calcium oxide, barium oxide, and boron oxide, and (2) calcium pyrophosphate.
Dissolved in the main component material of the binder is a luminescent component
that converts ultraviolet radiation of 254 nm to ultraviolet radiation of longer
wavelengths or to visible light. Examples of such a luminescent component include
an oxide of gadolinium (Gd), terbium (Tb), europium (Eu), neodymium (Nd), or dysprosium
(Dy), each of which belongs to lanthanum series, and an oxide of thallium (Tl),
tin (Sn), lead (Pb), or bismuth (Bi).
