No abstract

No abstract

The effect of the optical properties of phosphor screens on brightness and resolution has been studied both theoretically and experimentally. For this purpose, a computer model has been developed allowing the simulation of the light propagation in phosphor screens. From the model calculations the light output including its angular distribution, as well as the resolution, can be obtained. The influence of several screen parameters such as scattering and absorption behavior, reflectance of the Al film, and layer thickness on the screen performance is theoretically investigated. Experimentally, light output and resolution measurements have been carried out on phosphor powder screens varying in phosphor composition, screen weight, and grain size distribution. The experimental data corroborate the results of the theoretical model and let us conclude that the model can be used as a powerful tool for the design of the optical properties of phosphor powder screens with optimum light output and resolution.

Optical transitions between the 5 D 4 excited state of the Tb J , (4j) R configuration and the crystal-field split components of the (4j) C (5d) configuration are observed using highresolution laser excitation of Tb-doped powder samples at room temperature. Excited-state absorption spectra of Tb J ; in Y AG, Y AGaG, Y 2 Si0 5 , and LaOBr are presented. Superimposed on the broadband excitation spectrum of these transitions we find the relatively narrow 4/ ~ 4/ lines. We present a theoretical model for interpreting the 4/ ~ 5d transitions, which predicts a strict proportionality between the (4j) K 5 D4 ~ (4j) 7 (5d) and the ( 4j) R 7 Fb __ (4j) 7 (5d) transitions. This model is used to estimate the optical-absorption cross section for the former transitions. Although the terminating 4/ levels lie at the same energy as the 5d bands, the 4/-.4/ transitions can be interpreted on the basis of the J udd-Ofelt theory.We derived a method for calibration of the Tb J I 4/ ~ 5d fluorescence-excitation spectra from powder samples. For Y AG:Tb, the resulting optical cross sections were confirmed by directabsorption measurements on a Tb' '--doped epitaxial Y AG layer. To our knowledge, this is the first time that the probabilities for excited-state absorption to highly excited 5d and 4/ states in Tb' + have been obtained theoretically and experimentally from Tb-doped powder materials.

No abstract