Candoluminescence and radical recombination

Photoluminescence, Candoluminescence, and Radical Recombination Luminescence of Minerals... 

The candoluminescent and radical recombination spectra of willemite are shown in comparison with the UV-excited spectrum in Figure 10. The envelope of the main emission band at 530 nm is the same in all spectra but the radical recombination excitation brings out another feature at 613 to 642 nm not seen in the photoluminescence spectrum. Similar behavior is seen in other Mn2+ activated candoluminescent spectra (20)... 

The lunar transient events could be excited by protons in the solar wind but experiments with silicate minerals in proton beams show that the process is inefficient, quantum efficiencies from lxl0 4 to 1x10 , and given the concentration of protons in the solar wind the mechanism cannot account for the intensity of the observed luminescence (33). Another possibility is that neutral particles in the background solar wind or associated with disturbances on the sunfs surface provide the excitation source (34). This would be a process very similar if not identical to the candoluminescence and radical recombination luminescence observed in the laboratory. 

White W (1990) Photoluminescence, candoluminescence, and radical recombination luminescence of minerals. In Coyne L, McKeever W, Blake D (eds) Spectroscopic characterization of minerals and their surfaces. American Chemical Society, Washington, DC, pp 118-134 White W, Masako M, Linnehan et al (1986) Absorption and luminescence of Fe in single-crystal orthoclase. Am Miner 71 1415-1419... 

Energy Transfer Processes. Luminescence is a complex sequence of energy transfer processes. Figure 2 is a schematic of the most important of these for photoluminescence, cathodoluminescence, and candoluminescence. The ultimate source of energy is the excitation UV light, electron beam, ion beam, or radical recombination excitation. We are not concerned here about the triggered release of previously trapped energy such as occurs in thermoluminescence and triboluminescence. 

The intensity of the UV-excited band simply falls off with increasing temperature. The hydrogen radical recombination luminescence spectrum peaks at 40 C and then falls off rapidly. Nitrogen and water vapor radical recombination luminescence peaks near 320 C while the candoluminescent spectrum peaks at 178 C. 

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