Study of ultrafast carrier dynamics of nanostructured TiO2 films with and without CdSe quantum dot deposition using lens-free heterodyne detection transient grating technique

Ultrafast carrier dynamics of nanostructured TiO2 films with and without CdSe quantum dot (QD) deposition were studied using a lens-free heterodyne detection transient grating (LF-HD-TG) technique. The nanostructured TiO2 films were prepared with anatase TiO2 nanoparticles with an average diameter of 27 nm. CdSe quantum dots with an average size of 5 nm were adsorbed onto the TiO2 films by a chemical deposition (CD) technique. The relaxation processes of the photoexcited electrons and holes can be detected separately using the LF-HD-TG technique. For the TiO2 film without CdSe deposition, it was found that the photoexcited holes relaxed within 2 ps. For the CdSe QD deposited nanostructured TiO2 film, two decay processes with time constants of 2 ps (τ1) and 16 ps (τ2) were detected. The fast decay process was attributed to photoexcited hole relaxation due to trapping in CdSe QDs. The slow decay process mainly reflected photoexcited electron transfer from CdSe QDs to TiO2.