The melamine crystals formed in the aqueous THF solutions of TCNQ and melamine contain both TCNQ and DCTC -as impurity species. Importantly, the doped crystals are strongly luminescent. They are so luminescent that the red emission is visible to the naked eyes when a crystal is illuminated by a laser with a wavelength within the 485 nm absorption peak of DCTC -. The photograph in Fig. shows the photoluminescence on the spot of a 514 nm laser viewed through the long pass filter with a cutoff wavelength of 550 nm (FGL550S, Thorlabs).