Photoinduced fluorescence enhancement and energy transfer effects of quantum dots porous silicon

摘要

We investigate photoinduced fluorescence enhancement (PFE) and energy transfer effects of surfactant capped Cd/Se core and CdSe/ZnS core/shell quantum dots (QD) that emit at 630-650 nm adsorbed in and onto porous silicon (PSi) single layer films and microcavity devices. Evidence is presented for fluorescence resonance energy transfer (FRET) from the QD (emitter) to mesoPSi nanostructures (acceptor) that photoluminess between 650-850 nm. We also observe a strong PFE of QD emission adsorbed into meso porous silicon (mesoPSi) under continuous irradiation with 532 nm excitation light. New insight into the mechanism of PFE is gleaned from studies of PSi pore size and surface chemistry including native, H_2O_2, UV-ozone, and thermal oxides, andrnaminosilane coated thermal oxide mesoPSi. These treatments alter the photoluminescent characteristics of the mesoPSi and QD. The PFE effect on QD PL is largest on thermally oxidized microcavities. PFE is considerably weaker for CdSe QD adsorbed onto macroPSi, silicon wafer surfaces and especially for ZnS capped QD suggesting the PFE effect requires a close interaction of the QD core with oxidized substrate. It is plausible that mesoPSi (10-20 nm dia) mediates a more intimate contact compared to macro or planar Si wafer. The PFE effect dynamically increases the QD PL by passivating nonradiative state through oxidation and possibly through increasing the lifetime of nonradiative trapped state by coupling to surface vibrations.