Fig. 4. (a) Photographs of d-Xyl and PER crystals taken at 77 K under varying UV light wavelengths or after stopping the irradiation. (b) Excitation–phosphorescence mapping and the phosphorescence spectra with different excitations (td = 0.1 ms) of PER crystals at 77 K. (c) Trajectory of phosphorescence colors of PER crystals at 77 K, recorded by the change in the λex from 245 to 375 nm, in the CIE coordinate diagram.
