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

Photoluminescence (PL) intensity of porous silicon has been recorded in a s elected set of organic solvents. PL stability has been systematically exami ned 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 lengt h with the dielectric constant of the embedding medium. For values of the d ielectric constant larger than 20, the Onsager length becomes of the order of the nanostructure size, and no further quenching is observed. These resu lts show that materials of low-dielectric constant should be chosen for enc apsulating porous silicon without affecting its FL. (C) 1999 Elsevier Scien ce B.V. All rights reserved.