The effects of surface treatment on optical and vibrational properties of porous silicon. (por-Si) layers grown on p-type Si wafers by electroless etching technique were studied by FTIR spectroscopy and photoluminescence (PL). The results indicate a correlatiora between the PL intensity and the strength of the absorption bands induced by mulltihydride complexes (SiHn, n ≥ 2). However, similar correlation was also established for monohydride species as evidenced from the layers containing no multihydrides. Furthermore, a new band is observed at 710 cm-1 and assigned to multihydrides suggesting a ne it, local bonding environment in these layers. © 1995.