Mechanisms of photoluminescence sensor response of porous silicon for organic species in gas and liquid phases

Abstract

Photoluminescence response of porous silicon in presence of single organic analytes scales within the linear dynamic range with concentration of detected species. We present systematic study of changes in porous silicon photoluminescence intensity in the presence of precisely controlled amounts of linear aliphatic alcohols (from methanol to n-hexanol) in gas and liquid phases. From the concentration dependence of photoluminescence quenching we determined sensitivity of porous silicon sensor response. The sensor response sensitivity revealed nearly monotonous change within the homological set of n-alcohols in both gas and liquid phases. However, while in gas phase the sensitivity of sensor response rose with the length of alcohol chain, in liquid phase we observed the opposite behavior. The mechanism of sensor response in gas and liquid phases is explained by photoluminescence dielectric quenching. The strength of photoluminescence quenching is directly determined by dielectric constant and concentration of analyte in liquid phase whereas in gas phase it primarily depends on effective concentration of analyte inside porous silicon matrix. The thermodynamic equilibrium concentration of analyte inside porous silicon matrix is controlled by capillary condensation effect. A very good correlation between gas phase concentration and room temperature saturated vapor pressure of studied analytes and porous silicon photoluminescence quenching response was obtained.