Optical properties of TiO2 anatase – Carbon nanotubes composites studied by cathodoluminescence spectroscopy

Luminescence spectra obtained by electron bombardment (cathodoluminescence, CL) on TiO2 (anatase)/carbon nanotubes (CNT) composite, show only one visible band at 498 nm, while the spectra taken from pure anatase samples show two bands at 498 and 545 nm. We demonstrate that the visible luminescence bands are originated by TiO2 surface defects due to oxygen vacancies, and that this luminescence signal is independent of TiO2 mineral form (anatase or rutile). Moreover we obtain that the 545 nm band quenching in TiO2/CNT composites is caused by empty oxygen vacancies (OV) related to oxygen given from oxygen-rich pristine powder of carbon nanotubes. Our conclusions are also supported by X-ray photoelectron spectroscopy (XPS), SEM analysis and energy dispersed X-ray measurements (EDX). Furthermore we can confirm that the NIR TiO2 luminescence emission is linked only to the presence of Ti rutile form as described in several works in literature.

► Our results summarize CL experiments performed on anatase/CNT composite samples.
► The visible CL is linked to intrinsic impurities in TiO2 surfaces.
► The quenching of the 550 nm band is caused by addition of CNTs in the composite.
► Oxygen-rich CNTs addition fills O vacancies quenches the luminescence signal.