Fig. 6.

PL spectra of bare TiO₂ NTs (1), 10-cycle ZnO/TiO₂ NTs (2), and 25-cycle (3) ZnO/TiO₂ NTs measured at 300 K (a) and 20 K (b). The inset in a compares the PL spectra of 25-cycle ZnO/TiO₂ NTs measured at 300 and 20 K, and the inset in b shows magnified spectra 1 and 2 recorded at 20 K