Characterization of Dehydration-Induced Luminescence of Kaolinite

Abstract

Abstract--Dehydration-induced luminescence (DIL), the emission of light from a clay paste upon dehydration, was characterized experimentally for a colloidal kaolinite. The relationship between total photon count of the emitted light and film thickness is linear up to a thickness of 30/~m. The photon emission was obtained over a critical range of water contents (25-60%) of the oven-dry clay, and the kinetics of photon emission was presumed to be closely associated with the kinetics of film dehydration. Whether drying proceeded throughout the bulk or via a moving front was undetermined, but in either mode it was preceded by the formation of a thin dry film at the interface with the atmosphere. Grinding of the kaolinite for several minutes by mortar and pestle before paste preparation resulted in an overall increase of photon emission compared to unground kaolinite and in the formation of more than one emission peak, as well as a prolongation of the light emission. This effect on the kinetics of light emittance was observed for about two months after the application of the mechanical stress and suggests a means of detecting the mechanical stress history of a clay.An estimate was made of the spectral characteristics of the emitted light using optical filters and by incorporating tryptophan and salicylic acid into the kaolinite paste where they acted as fluorescent probes. The latter technique shifted the frequency of the light emitted by the kaolinite from the ultraviolet to the visible range where it was less effectively reabsorbed. The first method showed that the wavelengths of 97% of the emitted light was <460 nm and that 75% of the light had wavelengths <410 nm. The second method showed that the total intensity of DIL increased in the presence of fluorescence molecules, suggesting that the emittance was in the ultraviolet range.

Experimental investigation into the effects of meteoritic impacts on the spectral properties of phyllosilicates on Mars

“…Additionally, a minor broad peak appears at 585 nm in the shocked sample which is related to Mn 2+ activation (Figure c). Dehydration‐induced luminescence [ Lahav et al ., ] of the kaolinite samples was not observed. There is no significant CL color (blue) change observed in both un‐shocked and shocked (4.32 km/s) kaolinite samples (Figure S8).…”

Effect of Adsorbed Iron on Thermoluminescence and Electron Spin Resonance Spectra of Ca-Fe-Exchanged Montmorillonite

“…One of the principal photophysical properties of clay minerals is the capacity for electronic energy storage as evidenced by (1) thermal luminescence (TL) (Seigel et aL, 1968;Nishita and Hamilton, 1975;and Lemons and McAtee, 1983); (2) electron spin resonance (ESR); and (3) a variety of room-temperature luminescent phenomena related to dehydration, shock, and shearing which have been recently discovered and partially characterized (Coyne et al, 1981a(Coyne et al, , 1981bLahav et aL, 1982;Coyne et al, 1983Coyne et al, , 1984Lahav and Coyne, 1985;Coyne, 1985). This stored energy may alter surface reaction mechanisms and rates.…”

Spectroscopic Characterization of Minerals and Their Surfaces

“…It has not found general acceptance because spectroscopic studies show no long range perturbation by the surface on the water frequencies (120)(121). It is the opinion of this author, who has observed ultraviolet luminescence from 1:1 clays (which have low levels of exchangeable cations) at a critical moisture content representing many 10's of molecular layers of water (126)(127) that this controversy has yet to reach final resolution. Admittedly, the interactions producing luminescence are inter-particle rather than interlayer and attraction between kaolinite particles would be expected to be influenced by the presence of both oxygen and hydroxyl surfaces, but some structural and energetic features of these different clays are in common.…”