Fig. 3
a Fluorescence spectra of the NBDs with excitation wavelength changes from 320 to 520 nm. b UV-Vis absorption spectra of the NBDs. c Fluorescence spectra of the NBDs at different temperature, the inset is the plot of the fluorescence intensity of the NBDs as a function of temperature. d Fluorescence intensity and images of the NBD powders under the illumination of a 365-nm lamp for different duration and those of the NBD powders at different measuring temperature