Porous silicon in solvents: Constant-lifetime PL quenching and confirmation of dielectric effects

The time-resolved photoluminescence (FL) of luminescent porous silicon has been investigated insitu when porous silicon is immersed in chemically inert organic solvents. PL transients are re corded upon square-wave modulation of the excitation light. They are fairly well fitted with exponential curves. The obtained lifetimes lie in the 1-100 mus range, and decrease with increasing emission energy. At a given energy, the lifetimes exhibit a weak decrease when porous silicon is immersed in a solvent, whilst the PL intensity decreases by more than three orders of magnitude when the dielectric constant of the: solvent increases From 2 to 20. The weak variation of the lifetime indicates that the PI. quenching necessarily involves a decrease of the radiative recombination probability. This is accounted for in a model where the solvent-induced dielectric screening favours geminate pair dissociation.