Valence excitons and inner-shell excitons in gaseous and solid argon

Valence excitons from the 3p shell and core excitons from the 3s and 2p shells in gaseous and solid argon are studied within the envelope-function formalism. First, semiempirical model potentials for atomic excitons are considered; then solid-state effects, which include band structure and electron-hole screening, are taken into account. The problem of a sufficiently accurate account of the "band kinetic operator" is solved with first-order perturbation theory. A new interpretation of the excitonic spectrum originating from the 2p shell is given in terms of first-class exciton (1s) and third-class excitons (nd, n≥3) associated with a unique band edge.