Thanks a lot Dr. A Hameed for your answer. What I understand from your answer is that the broad spectrum say in the case of Ag/TiO2 is due to the presence of Ag2O. If I have only Ag/TiO2, then the spectrum will be like that of Au/TiO2. If so, then the absorbance in the case of Ag/TiO2 can not be attributed to the surface plasmon resonance of Ag nanoparticles rather it is due to Ag2O.