High- density silicon nanowires were grown on the n-(111) single crystal silicon wafer based on solid-liquid-solid mechanism using Au films as catalyst. Then silicon nanowires were doped with yttrium (Y) with high temperature diffusion method using Y2O3 powder as doping source. The experimental parameters were doping temperature of 900～1 100 ℃, doping time of 15～60 min and N2 flow rate of 0～400 sccm. The morphology of nanowires was measured with scan electron microscopy (SEM). The composition and crystalline orientation of nanowires were analyzed with X-ray diffraction (XRD). The measurement and characterization of excitation and emission spectrum of silicon nanowires were carried out with F-4600 fluorescence spectrophotometer. The SEM images show that the curved, winding silicon nanowires with uniformly size and high density were grown on the surface of silicon wafer. The average diameter and length of silicon nanowires are about 100 nm and several tens of microns, respectively. The photoluminescence spectra of undoped silicon nanowires were measured with an excitation wavelength of 214 nm at room temperature, which exhibits a broad blue emission in the range of 450～480 nm with the center peak of 470 nm. The blue emission band is derived from the oxygen vacancies in the amorphous SiOx shell of the Si nanowires. Also, the photoluminescence spectra of Y doped silicon nanowires were measured, which consists of a broad blue emission band in the range of 470～500 nm with the center peak located near the 488 nm and a narrow yellow-green luminescence band in the range of 560～600 nm with two emission peaks of 573.6 and 583.8 nm. The experimental results show that with the increase of doping temperature from 900 to 1 200 ℃, the strength of the yellow-green light emission band has experienced increase firstly and then decrease, the maximum value appears at 1 100 ℃. In addition to the temperature, a similar phenomenon was also observed by changing the doping time and nitrogen flow. The yellow-green luminescence intensity of Y doped silicon nanowires increases firstly and then decreases with the increasing of the doping time (from 15 to 60 min) and nitrogen flow rate (from 0 to 400 sccm), the maximum value appears at 30 min and 200 sccm, respectively. In order to explore the source of yellow-green emission band in the range of 560～600 nm of Y doped silicon nanowires, X-ray diffraction is carried out. The results show that two major compounds can be formed, namely, Y2Si2O7 and Y2SiO5 with high temperature diffusion Y into the silicon nanowires. We believe that Y3+ can introduce impurity energy levels in the band gap of silicon nanowires. Therefore, the luminescence mechanism can be described as follows: First, the silicon nanowires absorb photons, forming photo electrons in the conduction band. Then, electrons relax to the impurity levels. Finally, electrons jump to the valence band of silicon nanowires, and emitting yellow-green light.