Abstract:  The nanocrystalline Si(nc­Si)/SiO2 multilayers were deposited in a traditional plasma enhanced chemical vapor deposition(PECVD)system，and a two­step metal­assisted chemical etching method was employed to prepare porous Silicon nanowire arrays(Si NW)．The size of nc­Si could be controlled by adjusting the deposition condition，while the porosity density of the Si NW could be tuned through controlling stoichiometric proportions and etching time.The microstructure of two samples was characterized through transmission electron microscopy and scanning electron microscopy，then their fluorescence properties were measured by using the steady and time­resolved fluorescence spectrometer.The steady photoluminescence(PL)was measured under 325 nm He­Cd continues laser excitation，the PL centered at 900 nm for nc­Si/SiO2 multilayers was observed.Meanwhile，for the Silicon nanowire arrays，the PL peak was 720 nm.With decreasing the average size of nc­Si or increasing the porosity density of Silicon nanowire arrays，the PL intensity gradually enhances，while the PL peak remains unchanged.The time­resolved photoluminescence decay spectra were measured by utilizing an Edinburgh instruments(FLS980)fluorescence spectrophotometer.Two excitation sources were equipped，one was a EPL­375 picosecond(ps)pulse diode laser(λ＝375 nm，pulse duration 75 ps and repetition frequency 5 MHz)，the other one was a frequency­tripled Nd：YAG nanosecond(ns)laser(λ＝355 nm，pulse duration 6 ns and repetition frequency 10 Hz)．It is shown that the two kinds of material both exhibit microsecond(μs)fluorescence lifetime under nanosecond(ns)laser excitation，the microsecond(μs)PL decay could be attributed to the radiative recombination of photo­generated carriers via the oxygen­related localized states at the interfacial region.The enhanced PL and longer fluorescent lifetime could be ascribed to the increase of radiative recombination center.Meanwhile，all samples don’t have the nanosecond PL decay component when exited by picosecond(ps)laser.