Luminescence of nitrogen and neon atoms isolated in solid helium

On charged impurity structures in liquid helium

“…As it was shown earlier, luminescence of the IHC sample submerged in bulk He II can be stimulated by the temperature increase of ~ 0.1 K of He II [23]. The fast decay stage (obeying to an exponential law with τ = 15-40 s) of the thermostimulated luminescence was followed by longlived decay obeying to a hyperbolic law with much longer τ, up to 8⋅10 3 s [23]. In the present work we studied thermoluminescence spectra of IHC samples in He II during warm-up from 1.5 to 2.2 K (we will call such spectra as "cold" ones).…”

“…The lifetime of N( 2 D) atoms in matrices is greatly shortened, for example, from ~ 4.4⋅10 4 s in the gas phase to ~ 300 s and ~ 40 s for neon and nitrogen matrices, correspondingly [21,22]. As it was shown earlier, luminescence of the IHC sample submerged in bulk He II can be stimulated by the temperature increase of ~ 0.1 K of He II [23]. The fast decay stage (obeying to an exponential law with τ = 15-40 s) of the thermostimulated luminescence was followed by longlived decay obeying to a hyperbolic law with much longer τ, up to 8⋅10 3 s [23].…”

“…The lifetime of such N( 2 D) atoms was expected to be close to its gas phase value ~ 10 4 s. The green emission on 2 D-4 S transition was stimulated by "heavy" particle (N 2 molecule, atoms of neon, argon, or Kr) approaching N( 2 D) atom. The high sensitivity of the IHC samples to the temperature changes has been explained by the low value (about of 40 K) of the energy needed for helium shell rearrangement and meeting of N( 2 D) atom and "heavy" particle [23]. Nevertheless, the model did not allow us to explain the photostimulated luminescence of IHC samples submerged in bulk He II.…”

“…The earlier explanation of the thermostimulated luminescence of IHC samples submerged in He II was related to the model of van der Waals clusters consisting of single impurity atom or molecule surrounded by a shell of localized helium atoms [23]. The key point was the extremely weak perturbation of the helium shell on the central metastable N( 2 D) atom.…”

“…Some impurity centers as well as different structural defects of cryocrystals and clusters can be such electron traps. There are very broad distributions of electron traps in cryocrystals and clusters on the activation energy: the activation energies of 3.5 and 20 meV were determined for structure defects in neon nanoclusters [23] and cryocrystals [39], respectively, while the electron affinity energy of O( 3 P) atom is of 1.46 eV [40]. Therefore, thermo-or photostimulated electrons leave the traps and initiate neutralization reactions.…”