A phosphor admixture includes a phosphor powder and a number of radiation capture electron emitters. The emitters are dispersed within the phosphor powder. A phosphor screen includes phosphor particles, radiation capture electron emitters and a binder. The emitters and phosphor particles are dispersed within the binder. An imaging assembly includes a phosphor screen configured to receive incident radiation and to emit corresponding optical signals. An electronic device is coupled to the phosphor screen. The electronic device is configured to receive the optical signals from the phosphor screen and to generate an imaging signal.