Absolute luminescence efficiency of ion-bombarded solid argon

We have directly measured the absolute efficiency of the 9.8-eV $M$-band luminescence from the decay of ${\mathrm{Ar}}_2^{\mathrm{*}}$ excimers in solid Ar bombarded by 1.5-MeV ${\mathrm{He}}^{+}$ and 10–50-keV ${\mathrm{H}}^{+}$ ions. About 54% of the electronic energy deposited by the projectiles is converted to 9.8-eV luminescence energy, or about 5.5 photons per 100-eV deposited. The efficiency is also found to be independent of ion and ion energy for those tested over a range of stopping cross sections from 6.5 to 400 eV/${(10\mathrm{}}^{15}\hspace{0.5em}{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}\mathrm{s}/\mathrm{c}\mathrm{m}}^2).\mathrm{}$ This work clearly establishes the $M$ band as the major relaxation pathway for electronically deposited energy in solid Ar, a pathway that is an important source of radiation damage and sputtering and which can be affected by electron emission.