Voltage-dependent tuning of photoluminescence (PL) and electroluminescence (EL) spectra of porous silicon layers grown on n(+) and n(-) substrates has been studied using electrolyte contacts. It has been demonstrated that PL and EL tuning occur under accumulation conditions. A mechanism that explains both PL and EL tuning is proposed on the basis of a kinetic;"scheme of squares" that considers incremental electron injection into quantum-confined particles, leading to Auger quenching of photoexcited or electrochemically generated electron-hole pairs. The tuning effects are predicted to occur as a consequence of the dependence of electron accumulation on the energy of the conduction band, which is in turn related to particle size. PL and EL spectra have been simulated for an ensemble of particles of different sizes, and it is shown that the model correctly predicts all the experimentally observed characteristics of the voltage tuning.