The cathodoluminescence spectra of nine diamond samples at temperatures of 82-295 K were investigated. According to the presence of the N3a vibronic system with the zero-phonon line at 2.68 eV in the luminescence spectra, six samples were identified as natural. By the presence in the luminescence spectra of the 2.56-eV vibronic system and the unstructured band at 2.54 eV, associated with nickel, two samples were identified as synthetic, grown at high pressure and high temperature. Due to exciton luminescence at 5.271 eV and the absence of any spectral features of impurity nature, one sample was identified as synthetic, grown by the chemical vapor deposition. Based on the data obtained, the technique for identifying of natural and synthetic diamonds has been proposed.
Optical absorption spectra in the temperature range of 85-300 K and IR absorption spectra at room temperature of four diamond samples were studied. All samples demonstrated the GR1 vibronic system of a neutral vacancy. The absorption coefficient at the zero-phonon line at 1.673 eV decreased by the power law in the temperature range of 120-230 K. Outside this temperature range, the absorption on the neutral vacancy did not practically changed. The value of the absorption coefficient at the neutral vacancy correlated well with the densities of nitrogen impurity-defective NV-, N<sub>2</sub>Vand N<sub>4</sub>V-complexes.
UV lasing is studied in nitrogen and the N2-SF6 mixture pumped by a volume discharge initiated by a runaway-electron
preionised diffuse discharge (REP DD) produced in an inhomogeneous electric field. It is shown, that lasing at a
wavelength of 337.1 nm is observed at pressures up to 2.5 atm without any preionisation source. At a pressure of 0.5 atm
with the use of blade electrodes and the N<sub>2</sub> :SF<sub>6</sub> =10:1 active medium of length ~6 cm, the output laser energy of ~2 mJ
was achieved for the pulse power of 0.55 MW. The REP DD pumping regime is compared with the regime of pumping
by a volume discharge produced by a preionisation source.