Band spectra of cathodo-luminescence

Much has been published on the emission spectra of solid fluorescent materials when excited by various kinds of radiation, especially ultraviolet light. The study of the comparatively few cases of line emission, for example, by Tomaschek and by Deutschbein, has given precise results in contrast to the very variable data available for band spectra. The methods adopted in earlier work for determining the position of emission bands have frequently been inexact or liable to subjective errors. Lenard and his school (1928) used the spectrophotometer or even a direct vision spectroscope. Rothschild (1937) used photographic methods resembling those of absorption spectrophotometry, but in general the spectrophotometer has been employed most; it is unsuitable for the examination of cathodo- fluorescence on account of the difficulty of maintaining constant excitation during a long series of observations. In the present work, which is largely concerned with cathodo-fluorescence at room temperature, the spectra were photographed, the densities recorded by a microphotometer, and from the resulting curves the intensities in the original emission bands calculated. By a similar method Schellenberg (1932), working on ultraviolet excitation, and Kutzner (1937) on α-particle scintillations, obtained complex band systems which were analysed algebraically into hypothetical components. This was unnecessary for nearly all the materials considered below, which gave either single bands or complexes adequately separated by graphical methods.