Degradation of commercial Gd₂O₂S:Tb phosphor

The degradation of Gd₂O₂S:Tb phosphor was studied with Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL). The surface reactions were monitored with AES while the light output was measured with a PC2000-UV spectrometer. The CL of the Gd₂O₂S:Tb was excited with a 2 keV energy electron beam with a beam current density of 26 mA/cm². The CL and AES were measured simultaneously while the sample was bombarded with the electrons in an oxygen atmosphere. A comparison between the low energy peaks of the AES spectra before and after degradation showed significant differences in the shape of the different peaks. A linear least squares (LLS) method was applied to resolve the peaks. Elemental standards from Goodfellow were used in conjunction with the measured data to subtract the S and Gd peaks. A direct correlation between the surface reactions and the CL output was found. The CL decreased while the S was removed from the surface during electron bombardment. A new non-luminescent surface layer that formed during electron bombardment was responsible for the degradation in light intensity.