Silicon Nanoparticle Photophysics and Singlet Oxygen Generation

MANUEL LLANSOLA PORTOLÉS; PEDRO D. GARA; MÓNICA KOTLER; SONIA BERTOLOTTI; ENRIQUE SAN ROMÁN; HERNÁN B. RODRÍGUEZ; MÓNICA 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 acidmethyl 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 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 O2. Strikingly, the luminescence decay time on the order of 1 ns does not depend on the solvent or 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 determination of O2 and N2 adsorption isotherms at 77 K. The results obtained indicate that physisorbed O2 is capable of quenching nondiffusively 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 (