LUMINESCENT COLLOIDAL SILICON PARTICLES

Crystalline silicon particles, which are coated by an oxide layer, are prepared by combustion of silane. Red or orange luminescence is activ ated by etching them in a 1:1 cyclohexane-propanol-2 suspension by aqu eous hydrogen fluoride in the presence of air. The temporal changes in the luminescence intensity of the suspension (several days) are descr ibed. When a suspension of luminescent particles in cyclohexane is mix ed with polar solvents such as alcohol, ether and chloroform, a more o r less quenching of the luminescence (depending on the nature of the a dded solvent) occurs. Mixing with non-polar solvent such as carbon tet rachloride does not lead to quenching. Triethylamine and ammonia quenc h the luminescence extremely effectively. Sulfuric acid also quenches. The particles migrate in an electric field in different directions de pending on the chemical surface treatment. It is concluded that lumine scence occurs when the particles carry only a few oxidized centers on the surface, and the protonation state of these centers strongly affec ts the luminescence.