Porous silicon samples were prepared by electrochemical etching in HF-C

2

H

5

OH solution. Polished

n

type and

p

type (111) Si wafers with resistivities of 40-60Ω·cm

and 8-10Ω·cm

respectively

were used as substrates. A contact was made to the back of the wafer

which served as the anode and Pt as cathode. The typical etching current was 1-10mA.The samples show intense red colour luminescence excited by UV light or 488nm lino from Ar ion laser at room temperature. The PL band is rather broad with the full width at half maximum of about 0.31eV. The peak wavelength shifts from 770nm to 730nm as the etching time increases from one hour to 6 hours

keeping the etching current at 2mA. While increasing the current to 10mA

the peak position further shifts to 670nm. Such a large blue shift has also been observed when increasing measurement temperature. Infrared spectra show that there are Si-H

bond vibration absorptions at 2080-2100cm

-1

. 850-900cm

-1

and 640cm

-1

corresponding to the stretching

bending and wagging modes

respectively. Besides Si-H

n

bondings in porous Si

Si-F and Si-O bondings at 830cm

-1

and 1070-1120cm

-1

respectively

have also observed and the relative content of F and O atoms increases with the etching current.The structure of porous silicon consists of nanometre size and micrometer deep silicon columns produced by electrochemical ething. The visible luminescence in porous silicon is attributed to the radiative recombination of excitons confined at the quantum wires. The incorporation of H and F atoms in the sampler is considered as the terminatinators of the dangling bonds at the surfaces of the silicon wires

and may play an important role in keeping a high intense visible PL. Extending etching time or increasing oxygen content would thin the quantum wire

resulting in the blue shift of the PL spectra.