4 - Luminescence

Summary

Luminescence processes

Luminescence transitions may occur within localised defect sites, for example to give the characteristic line emissions of rare earth ions, narrow emission bands of chromium in ruby, or they may produce broad bands from charge transfer between defects. Overall, emission bands may vary greatly in width, but nevertheless the luminescence spectra provide a measure of specific defect types, and even offer some quantitative measure of the changes in defect concentrations. Since the excitation energy for luminescence may be provided by many routes, ion implantation is no exception and it frequently produces strong luminescence from insulating targets. This feature is often used as a means of aligning the ion beam and it is common practice to have defining apertures with silica plates to check the ion beam position visually. Such intense luminescence can reveal a number of features relating to the changing defect state of the target. For example, in many of the materials used to form optical waveguides by ion implantation there is a decrease in luminescence intensity which approximately follows the amorphisation in the crystal. Hence, one has a visual estimate of the progress of the amorphisation. Quantitative recording of the wavelength dependence of the signal, in terms of luminescence efficiency and spectral changes, should provide details on not only the defects pre-existing in the material but also the ion beam induced changes. Consequently, a number of research groups have used the luminescence produced during implantation to follow such modifications.

Lattices modified by the ion beam will show changes in their subsequent luminescence performance and the effects of implantation have been recorded in photoluminescence, laser emission, cathodoluminescence and thermoluminescence.