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 SiO2:0.134 mol% PbS nanoparticles were ground and annealed in atmosphere. Changes in the cathodoluminescence (CL) brightness and the surface chemical composition of the SiO2:0.134 mol% 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 54 mA/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, SiOx, 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.