(color online) (a) PL spectra of CDs and CD/TiO₂ nanocomposites with mixing mass ratios of 1:50 and 1:500 in deionized water in a 10 mm×1 mm quartz cuvette under 405 nm excitation, the samples for PL spectrum measurement are prepared by mixing the CDs and TiO₂ with magnetic stirring for 24 h, the concentrations of the CDs in the three samples are all the same (10 mg/L), (b) PL decays of CDs and CD/TiO₂ nanocomposites with different CD coverages in deionized water, excited with 405 nm, measured at 530 nm.