Thermoluminescence Excitation Spectra Research Articles

Thermoluminescent processes of MgAl2O4 irradiated at room temperature.

Two non-first-order kinetic peaks at about 350 and 500 K appear in the thermoluminescence (TL) spectra of single-crystal and polycrystalline ${\mathrm{MgAl}}_{2}$${\mathrm{O}}_{4}$ irradiated with ionizing radiation at room temperature. Among others, emission from ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ ions are observed. TL measurements at different wavelengths indicate that the emitting centers have different recombination probabilities. Thermally-stimulated-current and thermoelectric-power measurements, together with results on the TL excitation spectra with ultraviolet radiation, indicate that both processes are due to thermally released electrons from traps. The V centers also act as recombination centers leading to a complex emission band at around 4.9 eV. Experimental results and numerical simulations based on a recently proposed mathematical model suggest that the massive presence of lattice defects, as a result of the antisite disorder and the nonstoichiometry of synthetic spinel crystals, may have a strong influence on electron-trapping and -detrapping processes, leading to complex-kinetics TL phenomena.

Luminescence excitation of pure and impure BeO single crystals using synchrotron radiation

Absorption, reflection, UV and VUV luminescence excitation and thermoluminescence excitation spectra have been measured for BeO and BeOZn crystals in the energy range from 8 to 35 eV, using synchrotron radiation. The nature of electronic excitations in the fundamental absorption edge region is discussed; the value of the forbidden-gap energy, E g, is estimated as 10.6 eV for BeO. Intrinsic luminescence with a 6.7 eV maximum for BeO and impurity luminescence with a 6.0 eV maximum for BeOZn are due to the relaxation of both optically created self-trapped or impurity-trapped excitons. The multiplication effect of electronic excitations with E>2 E g (or E≥2 E ex for 6.7 eV luminescence) for beryllium oxide is due to the inelastic scattering of hot photoelectrons or hot photoholes.

Electron excitation and luminescence in Bi 4Ge 3O 12 and Bi 4Si 3O 12 crystals

Reflection, luminescence excitation and thermoluminescence excitation spectra have been measured for Bi 4Ge 3O 12 and Bi 4Si 3O 12 crystals in the energy range from 3 to 35 eV using synchrotron radiation. The reflection data are evaluated using a modified Kramers-Kronig method for extracting the information on optical constants of these crystals. The nature of electronic excitations in the fundamental absorption edge region is discussed, the value of forbidden-gap energy E g is estimated as 5.0 eV for Bi 4Ge 3O 12 and 5.4 eV for Bi 4Si 3O 12. Intrinsic luminescence with 2.5 eV maximum for Bi 4Si 3O 12 and 2.45 eV maximum for Bi 4Ge 3O 12 is due to both the relaxation of optically created excitons and recombination processes. The multiplication effect of electron excitations in E ⩾ 2 E g for these crystals is due to the inelastic scattering of hot photoelectrons and hot photoholes.

Charge transfer mechanisms in the thermoluminescence of MgO

The optical and thermal stability of the optical absorption spectrum and thermoluminescence (TL) of as-cleaved MgO samples subjected to ionizing radiation at room temperature has been studied. UV irradiation leads to V-center formation when light is absorbed in the Fe 3+ absorption bands. Under subsequent illumination in the V-band, Fe 3+ ions are again formed. X or γ irradiation increase the Fe 3+ band (4.3 eV) to a saturation value and produce the V band. The same three glow peaks at ~ 93,175 and 220°C are observed in X, γ or UV irradiated samples. Two maxima at ≈ 4.3 and 5.1 eV are found in the TL excitation spectrum. It is suggested that, as expected, cation vacancies charge compensate for the Fe 3+ ions. Charge and excitation transfer between both hole and electron traps and the impurity activators Fe, Cr, Mn and Ni determine the observed TL emission.

Photo- and thermoluminescence excitation spectra of zinc oxide single crystals

The information on the nature of the visible luminescence bands of zinc oxide is presently highly contradictory [1-5]. There is also relatively little data on the investigation of the excitation spectra of the green and yellowish-orange luminescence which is characteristic of ZnO [3, 5, 6]. It has basically been established that the visible luminescence of ZnO is excited well upon the absorption of quanta corresponding to the energy of an interband transition and during exciton absorption. In addition, the appearance of an intense excitation band with a maximum in the 375-385-nm region has been noted in the excitation spectrum of the green luminescence at 77~

ON THE ORIGIN OF LOW TEMPERATURE THERMOLUMINESCENCE IN NUCLEIC ACID BASES: EXCITATION AND EMISSION SPECTRAL STUDIES

Abstract. Thermoluminescence excitation spectra of adenine, guanine, thymine and 1,3‐dimethyluracil were observed to be similar to their phosphorescence excitation spectra. Intensity dependence studies of thermoluminescence induced by ultraviolet light suggest that thermoluminescence could not be due to biphotonic ionisation of the molecule by UV. Evidence is presented which demonstrates that the fluorescence component observed in thermoluminescence of some compounds may not be due to triplet‐triplet fusion. Further, phosphorescence and thermoluminescence measurements following excitation with monochromatic light at very low intensities and short durations have shown for both a linear dependence on excitation intensity. It thus appears that direct entry of the electrons from the traps into the singlet manifold is necessary for explaining the fluorescence component of thermoluminescence.

Effects of Ultraviolet Irradiation on KBr: Gd

AbstractThe results of UV irradiation on Gd3+ doped KBr single crystals were investigated. Thermoluminescence (TL) glow curves, excitation spectra, and optical absorption were measured in comparison with pure and Sr2+ doped KBr crystals. The concentration of anion vacancies was found to be markedly enhanced by the presence of impurity ions. TL excitation spectra of Gd3+ doped samples had maxima at the α band and at the 212 nm band, which is attributed to a localized exciton state perturbed by a Gd3+ ion. Results suggest that defects responsible for the TL are created by an excitonic process.

Effects of Competition in the Stabilization of Point Defects

The dependence of the number of point defects on the dose and on the wavelength of the exciting radiation has been studied in uv-irradiated alkali halides. The existence of various types of traps for the stabilization of defects and the occurrence of competition between these traps were assumed. Theoretical expressions were derived for the number of defects induced by the monochromatic uv radiation. These expressions were found to agree with the experimentally measured dose dependences, as well as the thermoluminescence excitation spectra. They included various previously derived functions as special cases. The observed superlinear dose dependence of the intensities of most glow peaks in NaCl is explained by the proposed mechanism.

Electronic Defect Structure of Single-Crystal ThO2by Thermoluminescence

Some electronic defects and the associated photoelectronic processes in Th${\mathrm{O}}_{2}$ are analyzed by utilizing the data from thermoluminescence (TL) and EPR measurements on a number of rare-earth-doped and undoped single crystals from various sources. (The EPR measurements were made by others.) Some fluorescence and absorption measurements are also ultilized. Some TL glow peaks in the undoped Th${\mathrm{O}}_{2}$ correlate with the annealing of EPR spectra which are associated with trapped electrons. The similarity of glow curves for different crystals, the lack of hyperfine EPR structure, and the dependence on rare-earth doping suggests that some of the major electron traps are associated with oxygen vacancies, which may be complexed. The TL and EPR were induced by uv excitation, which created electrons and holes which are trapped. Some of the hole traps are identified as rare-earth ions in cubic sites. The rare earths provide all of the TL and fluorescence observed in ${\mathrm{Li}}_{2}$O \ifmmode\cdot\else\textperiodcentered\fi{} 2W${\mathrm{O}}_{3}$ flux-grown Th${\mathrm{O}}_{2}$, and the total TL at saturation depends on the doping level. The TL excitation spectra and optical absorption measurements on ${\mathrm{Li}}_{2}$O \ifmmode\cdot\else\textperiodcentered\fi{} 2W${\mathrm{O}}_{3}$ flux-grown undoped thoria indicate a band gap of 5.75 eV which is larger than previously reported. The thermal activation energies are given for electron traps, and some indications of relative cross sections for electron or hole trapping or recombination processes are reported.

Excitation spectra and temperature dependence of luminescence and photoconductivity of diamond

Luminescence excitation spectra of type I and intermediate diamonds were measured at 80°K and at room temperature, and were found to show a fine band structure near the absorption edge (210–240 mμ). The photoconductivity excitation spectrum at 80°K showed inverted peaks (minima) at the wavelengths of the maxima in the luminescence excitation. At room temperature, the inverted peaks turned into direct peaks (maxima) in the excitation spectra of the photoconductivity. Inverted peaks were also observed in the thermoluminescence excitation spectra at low temperatures. On excitation with wavelengths of 220–240 mμ the photoconductivity was found to rise, and the luminescence to decrease on warming the crystals. On excitation with longer wavelengths, both were found to be temperature independent up to considerably above room temperature. The results are discussed and a model to account for the results is proposed.

Thermoluminescence of ZnS Single Crystals

The blue and green components of the glow of ZnS: Cu: Cl crystals were recorded separately. Thermoluminescence-excitation spectra taken for each of the components were found to be identical with the excitation spectra for the blue and green luminescence at steady excitation. Other measurements included the spectral distribution of the glow, saturation effects, effects of infrared radiation, and computation of activation energies. The activation energy for the blue peak was found to be about 0.14 ev, and that for the green\char22{}about 0.20 ev. From the shape of the peaks it was concluded that the recombination process is bimolecular in character.