Cathodoluminescence (CL)
Investigations and contributions to the interpretations were carried out by Prof. K. Ramseyer - karl.ramseyer@geo.unibe.ch - at the University of Berne, Institute of Geological Sciences, Berne (Switzerland) and Dr. J. Mullis, IMP, University of Basel (Switzerland) (See Lit. 26).
Visual and spectroscopic cathodoluminescence investigations were carried out to characterize the natural orangy-pink sapphires enhanced with the new E(IM1)-method.

Methods
Natural orangy-pink sapphires enhanced with the new E(IM1) method were prepared as 30 micrometer thick thin-section and coated with a semi-transparent Al film. An improved cathodoluminescence (CL) microscope (Lit. 25), with an energy of 25 keV, and a source current of 70 µA for photographic recording and 4 µA for spectrographic analyses, was used. The luminescence characteristics were recorded on Ektachrome 400 color slide film and developed at 800 ASA. The CL spectra between 400 and 900nm (10nm resolution) was recorded from a 200 µm spot using a PTI model 01-001 monochromator equipped with a Hamamatsu R928 photomultiplier. The monochromator was linked to the CL microscope by a flexible optic fiber bundle. The CL spectra were not corrected for the spectral response of the instrument.

Results CL
CL clearly documents that the corundum crystal has a homogeneous red luminescing core and a slightly brighter luminescing outer zone of similar thickness (Fig. 53).
Between the core and the outer zone, a transitional boundary exists with a lower luminescence intensity than the outer zone (Fig. 51 and Fig. 53). The red CL from both areas contains identical peaks, with peak positions indicative for Cr³⁺-induced luminescence (Fig. 52). LA-ICP-MS data confirms the presence of Cr but also Mg, Fe, Ti, Be and Ga are present (Fig. 53). As shown by LA-ICP-MS, a depletion of the elements Mg, Fe, Ti, Cr, and Ga is found in the outer zone of this sample and Beryllium is enriched.
The outer zone was formed after crystallization and reshaping of the crystal and thus represents the result of a treatment.
Further investigation on the interpretation of the CL data are in preparation (Ramseyer, Peretti and Mullis, in prep.).