Information Encoded in Cathodoluminescence Emission Spectra

Abstract

The development of cathodoluminescence (CL) phosphors for television and computer screens has been extremely successful in terms of colour quality and long-term stability of the screens but these achievements have been made in a semi-empirical fashion and do not imply the same degree of maturity for analytical uses of CL. This is unfortunately the case even though CL has more than a century of history, with numerous routine applications in geological and mineral studies. Indeed the first cited example was excitation of a natural crystal, diamond (Crookes 1879). Current mineralogical usage is often qualitative, with visual, or photographic, inspection of the luminescence. Information is provided by variations in intensity and colour which can be helpful in separating mineral composites, and certainly will clearly indicate the presence of zoning and the diversity of component minerals in a particular sample. One bonus of the CL equipment is that the electron beams generate characteristic X-rays from the target elements and thus from the complementary X-ray analyses it is possible to map some of the compositional variations within a sample and relate these to the emission patterns. CL is also compatible with electron microscopy imaging and can in principle be followed down to the micron grain size level. Thus for mineralogical studies the combination of techniques is clearly valuable (Yacobi and Holt 1986, 1990; Marshall 1988; Ozawa 1990; Walker and Burley 1991; Remond et al. 1992).