Observation of new band in stimulated luminescence of solid nitrogen

Recent results on the study of spontaneous and stimulated luminescence of solid nitrogen in the near-infrared (NIR) range are presented. Irradiation was performed with an electron beam of subthreshold energy in the dc mode. Three series of experiments were performed: (a) measurement of cathodoluminescence (CL) at different electron energies on samples of different thicknesses, (b) measurements of thermally stimulated luminescence (TSL) in combination with thermally stimulated exoelectron emission (TSEE) from pre-irradiated samples, and (c) recording of non-stationary luminescence curves (NsL) on selected wavelengths during gradual heating of samples under an electron beam. Three emission bands were recorded in the NIR TSL spectra of solid N2: 794, 802, and 810 nm which form the γ-group. The band at 810 nm in stimulated luminescence was detected for the first time. The positions of all three spectral features coincide in the spectra of spontaneous and stimulated luminescence, as evidenced by a comparison of the CL spectrum recorded at 5 K with the TSL spectrum recorded at the TSL maximum at 16 K. A comparison of the CL spectra obtained under different conditions showed that there is no complete correlation in the behavior of emission from the 2D state of the N atom and the γ-group, which could be expected in the case of the formation of the γ-band emitting centers via electron attachment to the N(2D) atom as it was suggested in [R. E. Boltnev et al., Phys. Chem. Chem. Phys. 18, 16013 (2016)]. The glow curves measured for these 3 bands were found to correlate with each other and with the TSEE yield. This finding indicates common origin of these bands and their connection with the neutralization reaction. The correlation of the γ-band NsL in the range of low temperatures (5–20 K) with the NsL measured at the 0-4 band of the a′1Σu−→X1Σg+ transition, which is the “fingerprint” of the tetranitrogen cation N4+ [E. V. Savchenko, et al. J. Phys. Chem. A119, 2475 (2015)], points to possible connection of the γ-band with the neutralization of N4+.