The development of luminescence methods to measure thermal exposure in lithic and ceramic materials
Thermometric analyses provide extremely useful information about heated archaeological materials and fire-damaged modern structures. A number of non-luminescence thermometry methods have been developed for analysing pottery firing temperatures. However, many of these methods are limited in analysis range and accuracy, or are time consuming, expensive and complex. In addition to these techniques there are a number of thermoluminescence (TL) thermometry methods but they are also limited in analysis range and the majority have been developed for specific thermometry problems. The aim of this study was to investigate the use of thermoluminescence (TL) and photostimulated luminescence (PSL) methods to develop rapid, precise, inexpensive thermometry techniques that were applicable to a wide range of thermal events and materials from archaeological and modern contexts. A basic theoretical treatment of luminescence kinetics in silicate systems was undertaken to develop an understanding of TL glow curve alterations arising from thermal exposure. Kinetic studies showed that a combination of temperature and duration parameters is expected for single trap systems. Kinetic theory was developed to produce a new first order multi-trap system which provides a theoretical means of separating temperature and time components, which may be applicable to synthetic phosphors. Additionally heat transfer solutions were investigated to examine the temperature distribution in heated solids and TL instrumentation. Isothermal annealing experiments on IAEA-F-1 potassium feldspar showed a highly precise progressive thermal exposure monitor, whereby the position of the first rise of an annealed TL glow curve is characterised by a linear increase in temperature and a logarithmic increase in time. First order kinetic simulations and initial rise measurements demonstrated a continuous linear distribution of traps in IAEA-F-1 feldspar. Using a high temperature TL system (maximum temperature 700°C) the progressive thermometry method was successfully applied to separated feldspar minerals and polymineral samples from archaeological (ceramics, burnt stones and hearthstones) and modern (fire damaged concrete) materials. PSL excitation spectroscopy showed potential thermometric behaviour but for some samples the sensitivity of the system was too low. Pulsed infra-red PSL showed there may be a limited trap distribution over which a small range of thermal exposures will operate. Combined TL/PSL measurements showed it may be possible to deconvolute temperature and time parameters.