Silicon Nanoparticle Photophysics and Singlet Oxygen Generation

MANUEL JOSE LLANSOLA PORTOLES; PEDRO DAVID GARA; MÓNICA KOTLER; SONIA BERTOLOTTI; ENRIQUE SAN ROMAN; HERNAN B. RODRÍGUEZ; MÓNICA C. GONZALEZ

LANGMUIR

AMER CHEMICAL SOC

Año: 2010 vol. 26 p. 10953 - 10960

0743-7463

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 Si3O6(C5O2H8), exhibit room temperature luminescence in the wavelength range from 300 to 600 nm upon excitation with 300 – 400 nm light. The luminescence shows vibronic resolution and high quantum yields in toluene suspensions, while a vibronicaly unresolved spectrum and lower emission quantum yields are observed in aqueous suspensions. The luminescence intensity, though not the spectrum features depend on the presence of dissolved O2. Strikingly, the luminescence decay time of the order of 1 ns does not depend on the solvent, nor on the presence of O2. 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 (1O2) phosphorescence detection, reaction of specific probes with 1O2, and the determination of O2 and N2 adsorption isotherms at 77 K. The results obtained indicate that physisorbed O2 is capable of quenching non-diffusively the particle luminescence at room temperature. The most probable mechanism for 1O2 generation involves the energy transfer from an exciton singlet state to O2 to yield an exciton triplet of low energy (< 0.98 eV) and 1O2. In aqueous solutions, excited silicon nanoparticles are able to reduce methylviologen on its surface.