Figure shows the luminescence maps for pure melamine (panel a), and the doped melamine crystals (TCNQ-Mel.) prepared with mole percentages of TCNQ to melamine of 0.04, 0.16, and 1.25 % (panels b, c and d). The integrated excitation and emission profiles of the maps are plotted in Fig. . All three crystals exhibit the UV luminescence peak of melamine centered at λ ex = 311 nm and λ em = 358 nm. In order to compare the maps for the crystals which are different in size, the intensity has been normalized by the maximum of this peak. The melamine crystal prepared with 0.04 % of TCNQ exhibits the visible emission peak (labelled as C 1 ) centered at λ ex ∼ 390 nm and λ em ∼ 454 nm. The C 1 intensifies as the mole percentage of TCNQ is increased. At 1.25 % of TCNQ, the second visible emission peak (labelled as C 2 ) discerns at λ ex ∼ 490 nm and λ em ∼ 600 nm. As the excitation and emission wavelengths for both C 1 and C 2 coincide with the UV-Vis absorption peaks (see panels c, d and e in Fig. , the C 1 and C 2 peaks can be attributed to the intrinsic emissions from the TCNQ and DCTC -, respectively. TCNQ in solid is basically non-luminescent as demonstrated in Fig. due to its very low quantum yield. The photoluminescence from TCNQ in the precursor solutions are quenched due to the resonance energy transfer to DCTC -(see the SI, section S3). Immobilized in crystalline melamine, TCNQ becomes highly luminescent, and the resonance energy transfer to DCTC is evitable, which makes the doped melamine highly luminescent in a wide UV-visible range.