Excitons in large-gap insulators: Solid neon

Excitons at the fundamental edge ($17<E<\mathrm{}22\mathrm{}$ eV) of solid neon are studied. The lowest transverse and longitudinal states ($n=1\mathrm{}$) are determined in the framework of the integral-equation approach assuming that the electron and the hole be confined to the same unit cell (one-site approximation). Numerical calculations are performed according to the general scheme previously applied successfully to valence and core excitons in solid argon. The lowest-conduction-band structure has been fully accounted for, using a detailed augmented-plane-wave calculation. Good agreement with the experimental results has been obtained. Higher excitons ($n>\mathrm{}1\mathrm{}$) are determined in the effective-mass approximation, modified to include the spin-orbit splitting of the valence band and the electron-hole exchange interaction, the latter being estimated from the excitation spectrum of gaseous neon. Full correspondence of the atomic transitions ${\left(2\mathrm{}p\right)}^6\to 2p^5\mathrm{ms} (m\ge 3)$ and $n\ge 1$ valence excitons in solid neon has been established. Relative intensities of the partners in the $n$th doublets ($n\ge 1$) are determined explaining the presence of only one exciton series in solid neon, unlike other rare-gas solids. Further structure above the threshold has been interpreted in terms of the joint density of states.