Luminescence of nitrogen and neon atoms isolated in solid helium Original Research Article

Investigations of metastable N(2D) and Ne(3P2) atoms isolated in solid helium have been carried out for the first time. The luminescence spectra and kinetics in the impurity helium solid phase (IHSP), with impurity centers N2, Ne, Ar, and Kr, show the sensitizing influence of a neighboring heavy particle on the forbidden N(2D-4S) transition. The extremely long-lived (τ≈104s) hyperbolically decaying afterglow and thermoluminescence of this transition have been observed in the IHSP. Thermoluminescence studies allowed the determination of the energy barrier for pair fusion of neighboring centers. In agreement with calculations the energy barrier of this process which determines the IHSP stability turns out to be E1 = 40 ± 4 K. The activation energy of the long-lived afterglow stage was found to be E2 ≈ 7 K, close to the energy of vacancy formation in solid helium. By using laser-induced fluorescence, Ne(3P2) atoms have been detected in superfluid helium and in the IHSP for the first time. Within an experimental accuracy of 0.18 Å their spectral lines were unshifted and unbroadened with respect to the gas-phase values.