Photoluminescence properties of SiO₂ surface-passivated PbS nanoparticles

SiO₂:PbS nanoparticle phosphors were successfully prepared by a sol-gel process. The crystallized lead sulphide (PbS) nanoparticles inside the amorphous silicon dioxide (silica, SiO₂) matrix were examined by X-ray diffraction and transmission electron microscopy (TEM) to estimate the particle size and distribution. The particles were in the size range of 10-50 nm. The TEM diffraction patterns showed the PbS particles to be cubic in structure. Two strong broad photoluminescence emission bands were observed, namely blue (450 nm) from the SiO₂ matrix and yellow-orange (560 nm) from the PbS nanoparticles. In bulk PbS emission occurs at ∼3200 nm, and the blue shift to the much shorter wavelength reported here is ascribed to quantum effects in the PbS nanoparticles. The emission spectra were strongly dependent on the excitation wavelength.