Emission spectra of solid rare-gas alloys

In this paper we present the results of an experimental study of the α-excited vacuum ultraviolet emission spectra of xenon-argon, xenon-krypton, krypton-argon, xenon-neon, krypton-neon, and argon-neon solid alloys in the temperature range 6-40 °K. Three mechanisms for electronic energy transfer to single impurity states and to impurity pairs were considered: (1) energy transfer from vibrationally relaxed homonuclear diatomic molecule of the host to Xe/Ar and to Xe/Kr impurity states; (2) energy transfer from the host vibrationally excited homonuclear diatomic molecule to Kr/Ar impurity states; and (3) energy transfer via impurity ionization or the formation of metastable states in neon alloys. The single impurity emission bands originating from the lowest Wannier states exhibit large red Stokes shifts reletive to the corresponding absorption bands, being close to the corresponding gas-phase transitions, and thus manifest the effect of medium relaxation around single impurity states. A similar effect is exhibited for diatomic molecules in pure solids and for excited impurity pairs. Qualitative information has been obtained regarding efficient nonradiative ralaxation processes between high Wannier impurity states. The emitting single impurity state involves in most cases the lowest lying, optically allowed, excited state. We have observed multiple trapping sites for the single impurity and for the impurity pairs in solid Ar and Kr but not in Ne. The population of these trapping sites is determined by the deposition temperature. Finally, spectroscopic evidence is obtained for the existence of heteronuclear rare-gas XeKr*and ArKr*diatomic molecules.