Preparations and luminescent properties of PbS nanoparticle phosphors incorporated in a SiO₂ matrix

A synthetic route for the preparation of luminescent PbS nanoparticles encapsulated in SiO₂ at room temperature by the sol-gel process is presented. The particle size and morphology of the PbS nanoparticles were observed by transmission electron microscopy (TEM). The particle sizes were estimated from the X-ray diffraction (XRD) peaks using the Scherrer's equation. The measured particle sizes were in the range of 10 to 50 nm inside the SiO ₂ matrix. The cathodoluminescence (CL) measured with a Fiber Optics PC2000 spectrometer showed the emission peak to be at the wavelength of 680 nm. The phosphor was degraded in an oxygen atmosphere. The chemical composition of the prepared samples was analyzed by an energy dispersive spectrometer (EDS). Xray photoelectron spectrometer (XPS) was used to measure the surface chemical composition of the SiO₂:PbS nanoparticles before and after electron degradation. 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 O 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.