Glow curves

Because the escape probability of carriers from trapping sites is proportional to exp(-fi/ D, the location of a glow peak on the temperature scale provides encoded information on the value of thermal activation energy E. Hence, a glow curve represents a spectrum of energies that are required to free carriers from the various species of traps in the material. 

The principal goal of TSC trap level spectroscopy is to experimentally determine, by comparison of model glow curve with measured ones, the characteristic parameters that govern the nonisothermal relaxation kinetics of the solid. 

For most experiments on nonisothermal TSR, simple cooling of the sample to the desired initial temperature and a linear increase in T after excitation are sufficient to obtain TSC and TSL glow curves. Some techniques require more elaborate heating cycles, the details of which depend on the relaxation mechanism under study and on whether it is necessary to discriminate between simnltaneously occurring processes, e.g., thermally stimulated depolarization and thermally stimulated conductivity (see Chapter 2). 

The occurrence of TSDC during a thermal scan of a previously excited ( perturbed ) material is probably the most direct evidence we have for the existence of electronic trap levels in the band gap of these materials. The main attraction of TSDC and related techniques as experimental methods for the study of the trapping levels in high-resistance semiconductors was their apparent simplicity. A TSDC spectrum (for historical reasons, frequently referred to as a glow curve ) usually consists of a number of more or less resolved peaks in current versus temperature dependence. The latter, in most cases, may be attributed to a species of traps. 

The expressions (2.1)-(2.6) are similar to those describing TSC processes obeying first-order kinetics and represent an asymmetrical glow curve the amplitude of which is a function of heating rate. 

Many polymers, after irradiation at low temperature, give off light when allowed to warm. This phenomenon of thermoluminescence depends not only on the chemical structure but also on crystal morphology. In polyethylene, for example, peaks in the thermoluminescence glow curve correspond, respectively, to the crystalline and the amorphous regions (9, 19, 22) (Figure 2). 

Figure 2. Glow curves of various polyethelenes with different ratios of crystallinity-amorphous components. Temperature rises from left to right. Peaks 0, y, where a is caused hy crystalline component, and y by amorphous...

The profile of the CTL intensity versus sensor temperature (glow curve) also depends on the kind of combustible vapor... 

Fig. 30 CTL glow curves from the catalyst heated at a rate of 0.5 °C/s in synthetic air after adsorption of vapor, a Adsorption of 100 ppm ethanol in air for 1, 2, 5, and 10 min. b Adsorption of 40, 60, and 80 ppm acetone for 2 min...

Figure 30 shows the CTL glow curves for the catalyst pre-adsorbed ethanol or acetone vapor. The catalyst is heated at a rate of 0.5 °C/s in synthetic air. The CTL intensity increases at high temperatures, and the total amount of CTL intensity L depends on the adsorption time At and the gas concentration C during adsorption. We can measure the gas at a very low concentration by measuring the value of L because L is proportional to the product of At and C in a region of low AtC where a Henry-type adsorption isotherm holds. 

Three kinds of temperature-programmed measurements have been performed. One is CTL measurement during heating after adsorption at room temperature, which was described in the previous section (Fig. 30). The profiles of the CTL glow curves reflect the temperature dependence of the pro-... 

In its basic design, the equipment is similar to a 2-D TL glow-curve system as described previously, but with the addition of a modified Twyman-Green, Michelson type, interferometer between the oven and the photomultiplier. As the sample is heated, the TL signal is recorded while the movable mirror of the interferometer is scanning a given optical path difference in a preset number of steps. The interference pattern corresponding to each one-way scan... 

The results may be displayed either as an isometric 3-D plot of intensity vs temperature and wavelength or as a contour map. Individual interferograms can also be summed to display a conventional 2-D glow-curve over the full temperature range. 

High Potassic Feldspars. A high potassic feldspar from Kingston, South Australia, (mole % K Na Ca - 81 18 1) represents a typical NTL spectrum for members of this group. Figures 2a and 3a show the 3-D and contour plots respectively. An emission band near 400 nm with FWHM of about 40 nm is prominent in the glow-curve. The NTL peaks occur between 250-350°C followed by another high temperature peak around 500°C. 

Figure 2. Typical glow curve for an ordinary chondrite meteorite (in this case Dhajala) showing how peak temperature (T), peak width (FWHM) and TL sensitivity (TL) are measured. TL sensitivity is the level of TL emitted at the peak divided by the same quantity for an arbitrarily chosen meteorite, Dhajala (14). (Reprinted by permission from ref, 14. Copyright 1983 American Geophysical Union.)...

Figure 9. Glow curves for the Sharps meteorite (type 3.4) before and after annealing at 755-855°C and 0.77-1 kbar for 168-174 h in the presence of water and sodium disilicate. (Reprinted by permission from Ref. 31. Copyright 1986 American Geophysical Union.)...

Figure 11. Two glow curves for the type 3.4 ordinary chondrite Allan Hills A77011 (which may actually be a fragment of the same meteorite as Allan Hills A77214) before and after annealing at 900°C for 200 h in a dry nitrogen atmosphere at atmospheric pressure. (Reprinted by permission from Ref. 33. Copyright 1984 MacMillan Journals.)...

Figure 18. Glow curves for two Shergottite meteorites with an explanation for the differences in glow curve shape based on two components whose relative abundance depends on maximum temperature and cooling rates. (Reprinted with permission from Ref. 30. Copyright 1986 Pergamon Press.)...

Fornaca-Rinaldi, G., and E. Tongiorgi The influence of grinding on the thermoluminescence glow-curves of limestones Summer Course on Nuclear Geology, Varenna, 1960, Laboratorio di Geol. Nucl., Pisa 254 (1960). 

Figure 2 (B) shows thermoluminescence bands generated by mature wheat leaves [curves (a) and (b)] and by greening wheat leaves grown under intermittent illumination [curves (c) and (d)]. The continuous curves are for materials illuminated for I minute at -60 °C [curves (a) and (c)], and at-20 °C [curves (b) and (d)] the dashed curves are for the same materials without prior illumination. Each thermoluminescence band has its own (approximate) emission temperature Zy band( -45 °C where the subscript V stands for variable location ofthe band), A-band (-10 °C), B,-band (25 °C), B2-band (40 °C) and C-band (+55 °C). The C band is the major emission band in etiolated leaves [solid curves in (c) and (d)] and is apparently unaffected by prior actinic illumination [dashed curves in (c) and (d)]. Illumination of fully greened, mature leaves at -60 °C produces a weak Zy-band at -45 °C, a weakened C-band at 55 °C, a strong composite B-band, with Bi-band at 20 °C and B2-band shoulder at 40 °C, which together form the composite B-band. When the mature leaves were illuminated at -20 °C instead and immediately cooled [curve (b)], the glow curve is quite different a prominent A-band appears at -15/-20 °C, while the (Bj+B2)-band is much weaker and the Zy band is barely observable. Thus the A- and B-bands appear to be complementary to each other in amplitude illumination at -60 °C produces a strong B-band and no A-band, while illumination at -20° C produces predominantly A-band and much less B-band. Both the A...

Fig. 4. (A) Glow curves for spinach-leaf discs after a series of flashes (f-numbers). (B) Thermoluminescence intensity at 35 °C plotted as a function of flash number. Figure source Rutherford, Govindjee and Inoue (1984) Charge accumulation and photochemistry in leaves studied by thermoluminescence and delayed light emission. Proc Nat Acad Sci, USA 81 1109.

The involvement of Qb has been independently confirmed by Wydrzynski and Inoue from the effect observed upon selective removal of Qb by a heptane/isobutanol extraction procedure that does not disturb the primary quinone Qa- The flash-induced thermoluminescence glow curve in the extracted chloroplasts is identical to that in the DCMU-treated chloroplasts, namely, the B-band is absent and in its place there is a D-band arising from charge recombination in [S2/S3 -Qa ]. By reconstituting lyophilized chloroplasts with native plastoquinone, the B band was restored. Also of interest is the observation that when phenyl-p-benzoquinone or 2,5-dimethyl-/i-benzoquinone was added to reconstitute the extracted sample, the glow curves were not only different from each other, but also did not display the normal, DCMU-generated D-band. These results indicate that the role ofthe extracted Qb in photosystem II may... 

R6. D DeVault, Govindjee and W Arnold (1983) Energetics of photosynthetic glow curves. Proc Nat Acad Sci, USA 80 983-987... 

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