Fig. 4

The PL spectrum for CQDs-1 in upper panel and CQDs-2 in lower panel at different excitation wavelengths λ _ex. In the upper panel, λ _ex are 370 nm (red), 380 nm (green), 390 nm (blue), 400 nm (light blue), 410 nm (deep pink), 420 nm (yellow), 430 nm (light green), 440 nm (dark green), 450 nm (light red), and 490 nm (dark olive green). In the lower panel, λ _ex are 420 nm (orange), 440 nm (blue), 460 nm (yellow), 480 nm (red), 490 nm (green), 500 nm (pink), and 510 nm (dark olive green). The inserts show the peak wavelength in the PL spectrum, λem, as the function of excitation wavelength