Cathodo-Luminescence of MgO

Abstract

The cathodo-luminescence spectra of different samples of MgO - fresh, previously exposed to cathode rays, heated in a Bunsen and oxy-coal-gas flame etc. - show different characteristics. For the fresh crystal we get a strong band with peak at 4550-4400 Å which weakens in intensity as the crystal receives increasing previous exposure to cathode rays. At the same time three bands in the red-yellow region get increasingly stronger. On heating the exposed crystal, the previous condition (the same as that of the fresh crystal) is restored except for an increase of luminescence in the ultra-violet. The phosphorescence and the fluorescence spectra are the same for the fresh crystal, but for the crystal heated after previous exposure to cathode rays the fluorescence spectrum extends farther into the ultra-violet than the phosphorescence spectrum. The spectra of heated samples also show marked differences from the spectrum of the fresh crystal, and in the case of the sample heated in an oxy-coal-gas flame a new band at 2450 Å is obtained which disappears on continued cathode-ray bombardment.