The 3D fluorescence spectra of samples 12–14 (see sample 12 in figure 7C) showed an emission peak centered at 512 nm with a band from ~470 to 630 nm that resulted in green color from H4 fluorescence. This emission feature increases at 395 nm excitation and maximizes at 470 nm. Similar to H3, the ZPL for H4 (496 nm) is not visible at room temperature but was clearly seen in liquid nitrogen–cooled PL spectra for these samples.
Both H3- and H4-related fluorescence emissions showed a broad fluorescence band at ~470 to 650 nm. But the H3 fluorescence peak is shifted to the higher-wavelength side and has a wider tail toward this direction, resulting in a yellowish fluorescence rather than the green fluorescence of H4 (figure 8).