Decay dynamics and quenching of photoluminescence from silicon nanocrystals by aromatic nitro compounds

The decay dynamics and the quenching of the photoluminescence (PL) from Si nanocrystals are investigated. Electron accepters whose reduction potential s lie below the conduction band (CB) edge of the Si nanocrystals quench the red emission from the Si nanocrystals. The quenching rate constants obtain ed from Stern-Volmer analyses for 3,5-dinitrobenzonitrile, 4-nitrophthaloni trile, 1,4-dinitrobenzene, 4-nitrobenzonitril 2,3-dinitrotoluene, 3,4-dinit rotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene are in the range of 1 0(6)-10(7) M(-1)s(-1) The quenching mechanism occurs via an electron transf er from the CB band of the Si nanocrystals to the vacant orbitals of the qu enchers. The PL decay profiles of the Si nanocrystals, in the presence and absence of the quencher, are well described by the stretched exponential de cay law. The band gap of the Si nanocrystals estimated from the present stu dy is larger than the PL peak energy. The results are consistent with a qua ntum-confinement model, where recombination of electrons and holes occurs i n a surface state. The ability of nitrotoluenes to quench the PL from Si na nocrystals could be used to develop a sensor based on Si nanostructures for the detection of explosives.