Luminescence induced by ion impact on alkali-halide crystals at high temperatures (-160 to 200°C)

Abstract

A study has been made of luminescence induced by 25-keV ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ion impact on pure alkali halides. The spectra generally exhibit two wide bands, the position of which depend on the type of crystal. A detailed investigation was made of the temperature and dose dependence of luminescence, and the effect of bleaching, in KCl and KBr. The peak intensity in the luminescent spectrum is independent of temperature from -160 to -70°C, rises to a maximum at about -10°C then falls monotonically for further increase in temperature. The dependence of intensity on dose is similar to published observations of $V_3$ center formation. The ioninduced luminescence is not influenced by irradiating the crystal with light in the $F$ band or by irradiating with white light. We propose that the ion-induced luminescence is due to the recombination of electrons from the conduction band with $V_3$ and $V_4$ hole centers. This proposed model is consistent with the known energies of $V_3$ and $V_4$ centers. After the surface was deliberately exposed to ${\mathrm{O}}_2$ we also observe an additional band characteristic of ${\mathrm{O}}_2^{-}$.