14 Earth and Planetary Science Letters, 77 (1985) 14-19 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands [41 Emission spectra of meteorites during thermoluminescence J.A. Strain 1, P.D. Townsend 1,2, B. Jassemnejad 2 and S.W.S. McKeever 1,2 i Mathematical and Physical Sciences, University of Sussex, Brighton BN1 9QH (U.K.) 2 Department of Physics. Oklahoma State University, Stillwater, OK 74078 (U.S.A.) Received August 12, 1985; revised version accepted November 29, 1985 The emission spectra of four ordinary chondrite meteorites of petrological type 5 have been recorded during thermoluminescence. Spectra from all four samples are similar. A very broad emission structure peaked near 470 nm and extending from 300 to at least 700 nm is found for the glow peaks from - 150 to 250°C. The higher temperature peak, 300-500°C, exhibits a different character with a narrow emission band near 400 nm. A tentative model for a luminescence site is offered. The broad similarity between the four samples is particularly interesting as the samples include chondrites of different shock history. The importance of the changes in glow curve spectra with temperature are noted for kinetic analyses of conventional glow curves. 1. Introduction Meteorites may be subjected to extreme condi- tions before arrival on earth including shock and heating during a break up collision of the parent body in space, irradiation, solar heating and entry into the earth's atmosphere. Such effects can in- duce major changes in physical properties includ- ing crystalline to glassy transitions plus minor changes in the microscopic defect structure. Both features influence thermoluminescence (TL) and this sensitive technique has been used in many meteorite studies. A mineral of prime importance is oligoclase feldspar, an Na-Ca-Al-silicate. This system closely resembles albite, NaA1Si30 ~ which is a corner member of the feldspar ternary phase diagram and can be modified continuously in solid solution to the anorthite system CaAI2SizO s. For the type 3 chondrites metamorphism may be in- duced by low levels of shock and Sears et al. [1] suggest the differences in TL sensitivity corre- spond to a varying glass to crystalline content of the oligoclase and they have used this to sub-clas- sify the group 3 chondrites. Of the various types of meteorites the petrological types 5 and 6 may show reduced TL sensitivity as a result of shock, or heat, and induced transformation of crystalline oligoclase into feldspathic glass. High-temperature laboratory treatments of albite have produced changes in TL sensitivity as well as in the emission spectra [2]. Sensitivity changes in type 5 or 6 meteorites have been attributed to shock and/or heating [3]; likewise spectra changes from shock effects were noted in cathodoluminescence of lunar plagioclase [4]. For a complete understanding of the defects involved in TL one should determine both the population of the charge trapping centres and the types of luminescence site. In principle, the trap- ping levels are sequentially emptied as the temper- ature is increased and measurements of the emis- sion spectra yield data on the various lumines- cence sites. Knowledge of the emission spectra is important if one analyses samples which contain either a mixture of minerals, both electron and hole traps or, if the relative importance of the luminescence sites is temperature dependent. In practice, for TL measurements with low light levels one makes a compromise between a strong signal to noise ratio and information on the emission spectra. Normal practice is therefore to record panchro- matic emission via a broad band optical filter. This approach can lead to serious errors in the assessment of the kinetics of the TL and of course it omits information on spectral variations. Emis- 0012-821X/86/$03.50 © 1986 Elsevier Science Publishers B.V.