Vapor-deposited CaWO4 phosphor

In this paper we describe the preparation, microstructure, and x-ray excited luminescence of vapor-deposited CaWO4 films up to about 50 mu m thick, comparing them to particulate CaWO4 phosphor screens, used in medical diagnostic imaging. Films that we e-beam evaporated on substrates heated at or above 500 degrees C were polycrystalline with the scheelite structure, while on unheated substrates, films were initially amorphous but became crystalline after annealing them in air above about 750 degrees C. Crystalline CaWO4 films irradiated with x-rays produced light emission peaked at 430 nm. The emission intensity depended on film thickness and grain size and was comparable to particulate CaWO4 phosphor screens. Because the vapor-deposited films also exhibited superior resolution, they are promising for diagnostic x-ray imaging.