Abstract

The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation have been investigated using a Sr90–Y90 beta emitter as the electron source. Spectral emission curves of uv-grade, optical-grade, and electron-irradiated samples of MgF2 and LiF, and of CaF2, BaF2, sapphire, fused silica, and uv-transmitting glasses were obtained over the 200–650-nm spectral range. Fluorescence yields, expressed as the number of counts in a solid angle of 2π sr/MeV of incident electron energy deposited [MeV−1 (2π sr)−1], were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively. Typical yields observed with a uv/visible sensitive bialkali cathode range from 10 MeV−1 (2π sr)−1 for uv-grade MgF2 to ≃200 MeV−1 (2π sr)−1 for CaF2. For comparison, sodium-activated cesium iodide, one of the most efficient scintillator materials, yields about 700 MeV−1 (2π sr)−1. High-purity fused silica has the lowest yield, approximately 6 MeV−1 (2π sr)−1. Optical-grade MgF2 and LiF, as well as electron-irradiated uv-grade samples of these two materials, show enhanced fluorescence due to color-center formation and associated emission bands in the blue and red wavelength regions. Large variations in fluorescence intensities were found in uv-grade sapphire samples of different origins, particularly in the red end of the spectrum, presumably due to various amounts of chromium-ion content. Phosphorescence decay with time is best described by a sum of exponential terms, with time constants ranging from a few minutes to several days. Phosphorescence intensity expressed as a fraction of the steady-state fluorescence intensity is an extremely sensitive measure of crystalline perfection and purity. This fraction ranges from a high of ≃ 10−2 for some fluoride samples to a low of ≤2 × 10−6 for fused silica. Application of the parameters obtained in this work to the analysis of recent flight observations on low light-level experiments yields good quantitative agreement with flight data from OAO-3, OSO-7, and Apollo 17.

© 1975 Optical Society of America

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