Cathodoluminescence Characteristics of Mn2+-Activated Willemite (Zn[sub 2]SiO[sub 4]) Single Crystals

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Abstract
Cathodoluminescence studies were made of Mn2+‐activated willemite single crystals using an electron microprobe and a simple interference‐type spectrometer attachment. Use of the microprobe allows single‐crystal cathodoluminescence measurements to be made on comparatively small (2 +‐activation was found to be partially polarized. The electric vector of emission was along a direction perpendicular to the c‐axis of the crystals. Examination of the emission spectra in the two perpendicular polarization directions, corresponding to the analyzer direction parallel to the c‐axis, and perpendicular to the c‐axis, showed a difference of about 100Aå in the emission peak positions. Measurements of spectra and integrated intensity of emission were also made as a function of manganese concentration. The intensity of luminescence was maximum for Mn concentration of 2.9 w/o (weight per cent). The peak position of the Mn2 + band was found to shift from 5160 to 5300Aå as the manganese concentration increased from just a trace to about 12 w/o. The polarized cathodoluminescence emission can be explained on the basis of crystal‐field theory and symmetry arguments. These arguments lead to the conclusion that the two Zn2+ sites in the willemite structure, which are occupied by the Mn2+ ions, have effective local symmetries of C3v and C1, respectively. The emission peak shift to longer wavelengths, as the manganese concentration is increased, cannot be explained by simple crystal‐field theory. A model showing emission from Mn2 +‐Mn2+ pairs dominating at higher concentrations, in comparison to emission from isolated Mn2 + ions, is proposed to explain this shift of emission peak to longer wavelengths.

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