Electron spin resonance and photoluminescence experiments were performed on freshly etched and oxidized porous material. The results indicated the presence of O-related centers (non-bridging O-hole center clusters) which consisted of similar core structures in as-prepared and oxidized porous samples. It was found that a direct correlation existed between the presence of these centers and a red photoluminescence that was observed in both freshly anodized and oxidized porous material. It was suggested that this emission process was the result of optical transitions in the O-hole centers.

S.M.Prokes, W.E.Carlos: Journal of Applied Physics, 1995, 78[4], 2671-4