Theory of Thermoluminescence and Related Phenomena

The following sections are included:

• Preface

• Contents

Thermally Stimulated Processes (TSPs) are a group of physical phenomena in which a certain property of the material under study is measured as a function of temperature. Usually, the property is initially perturbed from a stable configuration, and is thermally stimulated back to equilibrium by raising the temperature. Typically, the property in question is measured during the heating of the sample, although isothermal measurements also qualify as TSPs. In many instances, the initial perturbation occurs when the specimen under investigation undergoes a process of excitation at the starting temperature, which may be ambient temperature (typically, room temperature, RT) but, in principle, it can be any other temperature. Typically, the process of excitation may be an irradiation of the sample by ionizing radiation or ion bombardment, but other possibilities exist such as applying pressure on the specimen. It is important to realize that, in these circumstances, the temperature-dependent property is a functional, not simply a function. That is the value of the property during heating is not repeated during cooling. Re-excitation of the specimen is necessary in order to repeat the measurement…

The following sections are included:

• Basic Concepts of Luminescence in Solids

• Phosphorescence

• Elementary Theories of Thermoluminescence
  • TL as a Thermally Stimulated Process
  • Quasiequilibrium
  • First-Order Kinetics (Slow Retrapping)
  • Second-Order Kinetics (Fast Retrapping)
  • General-Order Kinetics

• Advanced Theories of TL
  • Multiple Trapping and Recombination States
  • Interactive Kinetics
  • Continua; Trap Distributions
  • Schön-Klasens Kinetics
  • Q- and P-Function Analysis
  • Tunneling
  • Localized Transitions

• Emission Spectra
  • TL-versus-Temperature-versus-Wavelength
  • Re-absorption
  • Thermal Quenching

• The Validity of the Arrhenius Law

• References

The following sections are included:

• General Considerations

• Analysis of Phosphorescence
  • First-Order Decay
  • Second-Order Decay
  • General-Order Decay
  • Becquerel’s Decay Law
  • Continua
  • TL-like Presentation of Phosphorescence

• The Initial Rise Methods

• Peak Shape Methods
  • Half Maximum Intensity Methods
  • Inflection Points Methods
  • Hyperbolic Heating Functions
  • Comparison of the Different Shape Methods

• Methods of Various Heating Rates
  • Advantages and Limitations

• Curve Fitting
  • Principles
  • Equations and Fitting Procedures
  • Some Experimental Examples

• Dealing with a Given Glow Curve

• References

The following sections are included:

• General Considerations and Experimental Evidence
  • Superlinearity
  • Supralinearity

• More Experimental Evidence

• Competition During Excitation

• Competition During Heating

• Combined Competition in Excitation and Heating

• Dose-Rate Effects

• Non-Isotropic Distribution of Traps and Centers

• Track Interaction Theory

• Sensitization Effects
  • Relationship between Superlinearity and Sensitization
  • Sensitivity Changes due to Annealing
  • The Pre-Dose Effect

• References

The following sections are included:

• Optical Processes and TL

• General Optical Processes in Solids
  • Optical Transitions and Optical Trap Depths
  • Photoionization Cross-Section

• Optical Bleaching
  • Kinetics
  • Wavelength Dependence
  • Thermal Assistance

• Phototransferred TL (PTTL)
  • General Observations
  • Models

• Optically Stimulated Luminescence (OSL)
  • Constant Excitation Intensity (cw OSL)
  • Non-Constant Excitation Intensity
  • Excitation Spectra

• Optical Generation

• References

The following sections are included:

• The Integrals in the Theory of Thermoluminescence and Other TSPs

• Numerical Solutions to the Differential Equations
  • Partial Separation of Variables
  • The Runge-Kutta Methods
  • Utilization of a Monte Carlo Method for Evaluating TL and TSC Curves
  • Using Approximate Integro-Differential Equations for the description of Complex TL Curves
  • Applications of Analog Computers to the Analysis of Thermally Stimulated Processes

• Peak Fitting and Deconvolution Methods for Analyzing Complex Glow Curves
  • Peak Fitting
  • Deconvolution

• References

The following sections are included:

• Radiation Dosimetry
  • Dosimetry Applications
  • General Properties of TLDs
  • Some Example TLD Materials

• TL Dating of Archaeological and Geological Samples
  • Introduction
  • Evaluation of the Annual Dose
  • Authenticity Testing of Art Objects
  • Pre-Dose Dating
  • TL Dating of Geological Specimens
  • Optical Dating and Related Effects

• References

Several physical and chemical effects are similar in certain ways to thermoluminescence. In some cases, like thermally stimulated conductivity (TSC) and thermally stimulated electron emission (TSEE), the effects are inherently related to TL and, therefore, in many cases there is a point in measuring them simultaneously with TL, as will be shown in Ch. 9. In other phenomena, such as thermal desorption of gases from the surface of a solid or in differential thermal analysis (DTA) and differential thermogravimetry (DTG), there is a close analogy between TL and the effect in question, but not necessarily a direct relation. In all these phenomena, a certain property of the material under examination is measured as a function of temperature. Of course, not all properties measured as a function of temperature qualify to be included in this group of phenomena. In most cases, an initial excitation of the sample is required prior to the heating, for example, an irradiation of the sample. This, however, can be replaced by some other physical initiation of the process in some of the other phenomena. For example, even in some rare cases of TL, applied pressure can induce the effect…

The following sections are included:

• Simultaneous TL and TSC Measurements
  • General Considerations
  • The Method for Evaluating the Recombination Probability
  • Examples: Insulating and Semiconducting Diamonds
  • The Shift between a TL Peak and the Accompanying TSC Peak
  • Information about Models from Simultaneous TL-TSC Measurements
  • The Determination of the Density of Deep Traps by Simultaneous TL-TSC Measurements
  • Experimental examples of some TL-TSC Measurements

• Simultaneous Measurements of TL with Other Physical Phenomena
  • TL and TSEE Measurements

• TL and the Concentration of Trapped Carriers as Reflected by Absorption and EPR
  • TL and Optical Absorption Measurements
  • Simultaneous Measurements of TL and EPR (ESR)

• References

In the present chapter we are going to include several different topics, mostly concerning thermoluminescence but some related to other thermally stimulated processes, which are important, but are not an integral part of the subjects discussed so far. We start with the important subjects of thermal fading and anomalous fading of TL which are of interest with respect to many thermoluminescent materials, and in particular, concerning those materials used for dosimetry and dating. We continue with other, more specific phenomena which are interesting due to the particular effect described, e.g. the extremely high values of E and s found for “peak 5” of LiF. Some miscellaneous TL effects in “exotic” materials such as food samples, extraterrestrial materials, and high temperature superconductors will also be discussed.

Throughout this book, we have attempted to describe different experimental and theoretical approaches to the study of thermally stimulated phenomena. These approaches permit the utilization of these phenomena in, for example, the extraction of numerical values for certain physical parameters from the materials under study, or allow possible practical applications in a variety of arenas. We have mentioned some of the experimental difficulties inherent in the measurement of TL and its related phenomena - some of which can be measured simultaneously, or separately. In the present section we summarize, by way of conclusion, some of the main highlights of the preceeding chapters. We facilitate this by separating the discussion into the topics of models, analysis, properties, and applications - under the broad heading of Prospects and Limitations. Finally, since all the TL and related phenomena discussed in the book have to be recorded experimentally in some fashion, we conclude with a description of the Instrumentation used in the experimental measurement of TL glow curves.

The following sections are included:

• Subject Index

• Author Index