Synthesis and degradation of the PbS nanoparticle phosphors embedded in SiO₂ (SiO₂:PbS)

PbS nanoparticle phosphors embedded in SiO₂ were synthesized at room temperature by the sol-gel method. The as-prepared SiO₂:0. 134mol% PbS nanoparticles were ground and annealed in atmosphere. Changes in the cathodoluminescence (CL) brightness and the surface chemical composition of the SiO₂:0.134mol% PbS nanoparticle powders were investigated using a Fiber Optics PC2000 spectrometer for CL and Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) for the surface chemical analysis. The chemical composition of the powders was analyzed by an energy-dispersive spectrometer (EDS). The CL intensity decreased when the powders were irradiated with a beam of electrons at 2 keV energy and a, beam current density of 54mA/cm² in an ultra-high vacuum chamber at oxygen (O₂) pressures ranging between 5 & 10^-8 and 2 × 10^-7 Torr for several hours. The O₂ Auger peak-to-peak height (APPH) decreased as the CL intensity decreased. XPS analysis on the degraded spot showed the development of characteristic SiO, SiO_x, and elemental Si peaks on the low-energy side of the SiO₂ peak. The desorption of O₂ from the surface, which resulted in a decrease in the CL intensity is attributed to the dissociation of SiO₂ into elemental Si and O₂ by the electron bombardment. The degradation was less severe at higher oxygen pressures. PbSO₄ was also formed on the surface during the electron beam degradation process.