Photoluminescence quenching of porous silicon in organic solvents: Evidence for dielectric effects

Photoluminescence (PL) intensity of porous silicon has been recorded in a selected set of organic solvents. PL stability has been systematically examined on the time scale of the measurements in order to carefully exclude any interfering chemical effects. A three-order-of-magnitude drop is found by increasing the value of the dielectric constant of the solvent from 2 to 20. This spectacular result can be quantitatively accounted for in terms of a geminate recombination mechanism and of the variation of the Onsager length with the dielectric constant of the embedding medium. For values of the dielectric constant larger than 20, the Onsager length becomes of the order of the nanostructure size, and no further quenching is observed. These results show that materials of low-dielectric constant should be chosen for encapsulating porous silicon without affecting its PL.