OPTICAL ABSORPTIONS OF NANOSCALED COTIO3 AND NITIO3

Photoacoustic spectroscopy has been used to study various sizes of nan oscaled CoTiO3 and NiTiO3 powders. Three absorption bands (or peaks) a re observed from ultraviolet to near-infrared (350-1200 nm) in the pho toacoustic spectra. The analyses indicate that the absorptions located around 525 nm for CoTiO3 and 445 nm for NiTiO3 are induced by the tra nsition of free excitons, but the absorptions located around 590 nm fo r CoTiO3 and 505 nm for NiTiO3 are related to that of bound excitons. Besides, the absorptions located around 840 nm both for CoTiO3 and NiT iO3 are corresponding to the electronic transition of additional energ y levels caused by defects and impurities. The behavior of the charact erized absorptions strongly depends on the grain sizes. (C) 1997 Elsev ier Science S.A.