Figure 2

Changes in the photoluminescence of CdTe nanocrystals upon the addition of methylene blue. Panel a Quenching of PL of 3.3-nm CdTe NCs solution at increasing dye concentration (“a”–“g”). Inset: PL spectra for samples “3.3 f” and “3.3 g” reveal the complete quenching of dye molecules. Panel b Comparison of photoluminescence quenching curves for 2.8-nm and 3.3-nm NCs samples. Photoluminescence intensity against the number of MB molecules per NC for 2.8-nm (closed square) and 3.3-nm (closed circle) NCs shows that 3.3-nm NCs are quenched more by the same number of MB molecules. Difference could be attributed to the larger spectral overlap with dye’s absorption band for this NCs sample. Panel c Photoluminescence measurements of 2.8-nm CdTe NCs/MB mixtures at 633-nm excitation. At 633-nm excitation, the NCs are not excited and only emission from MB is observed, which decreases in accordance with the concentration of MB in samples “a”–“g”. The inset shows the emission spectra of the last two samples in the 2.8-nm NC series, normalized on absorption at excitation wavelength (633 nm). The two spectra overlap each other, so there is no quenching of MB emission when QDs are not excited