Luminescence from PSi

In 1990, Canham observed intense visible photoluminescence (PL) from PSi at room temperature. Visible luminescence ranging from green to red in color was soon reported for other PSi samples and ascribed to quantum size effects in wires of width 3 nm (Ossicini et al, 2003). Several models of the origin of PL have been developed, from which we chose two. In the first (the defect model), the luminescence originates from carriers localized at extrinsic centers that are defects in the silicon or silicon oxide that covers the surface (Prokes, 1993). In the second model (Koch et al., 1996), absorption occurs in quantum-confined structures, but radiative recombination involves localized surface states. Either the electron, the hole, both or neither can be localized. Hence, a hierarchy of transitions is possible that explains the various emission bands of PSi. The energy difference between absorption and emission peaks is explained well in this model, because photoexcited carriers relax into surface states. The dependence of the luminescence on external factors or on the variation of the PSi chemistry is naturally accounted for by surface state changes. 

1 PL emission from the electrochemically prepared PSi layer on wafer in gas phase and different atmospheres nitrogen (Iim IX)) and oxygen Inset evolution of the PL maximum peak position with 

The PL quenching measurements of sensor elements based on prepared PSi, oxidized PSi and methyl-lO-undecenoate functionalized PSi are reported by Dian et al. (2010). It was demonstrated that relatively simple functionalization of the PSi surface via oxidation and hydrosilylation with methyl-lO-undecenoate substantially modifies the PL quenching response in the presence of polar analytes, as compared with H-terminated PSi surface. 

PSi and porous polymer substrates for optical chemical sensors are discussed by Hajj-Hassan et al. (2010). They were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors. 

A PSi microcavity was exposed to the saturated vapor of ethanol. The ethanol substitutes the air inside the pores and leads to a rise in a progressive monotonic red shift of the interference pattern of the PL spectrum. Moreover, the PL intensity of the cavity peak oscillates over time. Both effects are sequences in the progressive change of the refractive index of air and ethanol. Large, repeatable and selective red-shifts in the reflectivity spectra of PSi microcavities have been registered following exposure to 

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