Silicon Nanoparticle Photophysics and Singlet Oxygen Generation

Abstract

The effect of molecular oxygen and water on the blue photoluminescence of silicon nanoparticles synthesized by anodic oxidation of silicon wafers and surface functionalized with 2-methyl 2-propenoic acid methyl ester is investigated. The particles of 3 +/- 1 nm diameter and a surface composition of Si(3)O(6)(C(5)O(2)H(8)) exhibit room-temperature luminescence in the wavelength range 300-600 nm upon excitation with 300-400 nm light. The luminescence shows vibronic resolution and high quantum yields in toluene suspensions, while a vibronically unresolved spectrum and lower emission quantum yields are observed in aqueous suspensions. The luminescence intensity, though not the spectrum features, depends on the presence of dissolved O(2). Strikingly, the luminescence decay time on the order of 1 ns does not depend on the solvent or on the presence of O(2). To determine the mechanisms involved in these processes, time-resolved and steady-state experiments are performed. These include low-temperature luminescence, heavy atom effect, singlet molecular oxygen ((1)O(2)) phosphorescence detection, reaction of specific probes with (1)O(2), and determination of O(2) and N(2) adsorption isotherms at 77 K. The results obtained indicate that physisorbed O(2) is capable of quenching nondiffusively the particle luminescence at room temperature. The most probable mechanism for (1)O(2) generation involves the energy transfer from an exciton singlet state to O(2) to yield an exciton triplet of low energy (<0.98 eV) and (1)O(2). In aqueous solutions, excited silicon nanoparticles are able to reduce methylviologen on its surface.

Electric-field-induced band bending on GaN: in situ effects of electron beam irradiation on time-dependent cathodoluminescence

“…Initially, our proposed phenomenological model, featuring an environmentally derived adsorbed layer, agrees with previous reports that emphasize the impact of water adsorption on electric charge transport at the Nanoscale [30], and the feasibility of physisorbed O 2 to quench Si nanoparticle luminescence at room temperature [30]. Furthermore, humidity has reportedly produced deleterious effects on organic thin film transistors [32].…”

“…Indeed, Dierre et al [1] found that NBE-CL signal could either increase or decrease upon t-evolved e-beam irradiation as a function of surface termination. In fact, the suitability adsorbed surface species (molecular oxygen and water) to strongly modify time-dependent luminescence at room temperature has been confirmed recently [30].…”

“…8), GaN was purposefully exposed to ambient and immediately irradiated. There is evidence to suggest that water molecules present at the surface of a semiconductor can be ionized in the presence of an electric field, leaving the surface slightly positively charged H 2 O > e − H OH ⋅ [30,42]. As discussed earlier, in HAS, positive surface charge is held by free electrons in n-GaN, which accelerates incoming beam electrons into the interaction volume, inhibiting SE emissions and leading to a dark contrast in SEM [inset Fig.…”

Singlet oxygen mediated DNA degradation by copper nanoparticles: potential towards cytotoxic effect on cancer cells

“…More recent trend in this area has been testing of metal nanoparticles such as gold and platinum nanoparticles for DNA degradation studies [14,15]. Use of metal nanoparticles can be in particular advantageous in generating singlet oxygen [16,17]. A recent report by Geddes and coworkers demonstrated that the presence of metal nanoparticles can enhance singlet oxygen generation [18].…”

Facile synthesis of biocompatible gold nanoparticles from Vites vinefera and its cellular internalization against HBL-100 cells

“…A more current development in this area has been testing of metal nanoparticles such as gold and platinum nanoparticles for DNA degradation studies (Shen et al 2009; López et al 2010). Use of metal nanoparticles can be in particular advantageous in generating singlet oxygen [42 and 43] (Lipovsky et al 2009; Portolés et al 2010)…”