F. Aramu

Kinetics of the carrier storage in thermoluminescent phosphors

Abstract The problem of the thermoluminescence building-up, that is of the carrier production and storage during the phosphor excitation, is faced by the same kinetic model which allows for the thermoluminescent emission, that is, for the carrier recombinations. Equations are given suited to perform quantitative comparisons with the experiment. Measurements on ZnS and AgCl crystals show the reliability of the model and yield values for the ratio of retrapping to recombination probabilities in agreement with those found with emission experiments.

Thermoluminescence of naphthacene

Abstract Results on the naphtacene thermoluminescence, UV excited at liquid N 2 temperature, are compared with previous ones on the phenanthrene. Some evidence is obtained about the existence of a two-step process for the recombination of the electrons thermally released from traps.

Thermoluminescence of polyacenes and related hydrocarbons

Abstract The thermoluminescent emissions of some aromatic hydrocarbon crystals have been investigated as excited at liquid N 2 temperature by UV light. Diffuse scattering measurements have been also performed for determining the absorption and excitation spectra. The results are interpreted on the basis of a kinetic model, which accounts for the photoluminescent properties too. Evidence is obtained as to the effect of the molecular structure on the thermoluminescent emission efficiency.

Depth of electron traps in silver halides by the thermoluminescence spectra method

Abstract The thermoluminescent emissions of AgCl and AgBr crystals have been investigated as excited at liquid N 2 temperature with UV light. The spectra of both halides were found to exhibit a single glow peak, with maxima at 140 and 124 ° K respectively. Analysis of the data yields an activation energy of 0.13 eV for AgCl and 0.096 for AgBr. The trapping centres are identified with Frenkel defects and evidence is obtained in favour of the carrier trap situation presupposed by the Mitchell and Mott model for the latent photographic image formation.

On the thermoluminescence build-up in molecular crystals

Abstract Measurements were performed on the thermoluminescence build-up of phenanthrene crystals UV excited at liquid N 2 temperature. Kinetic investigations show that the passage of electrons from excited molecules to traps takes place by means of a direct process, without the intervention of the conduction band states. Arguments are advanced to point out the possible role of Frenkel excitons in this process.

A simplified procedure for the thermoluminescent glow spectra analysis

Abstract A method is proposed which, starting from kinetic equations, allows us to determine the parameters involved in the thermoluminescent process. The method, unlike some previous ones, does not require any troublesome calculations, and thus turns out to be readily applicable. An application is performed, considering the AgCl thermoluminescence.

Thermoluminescence of phenanthrene

Abstract The thermoluminescent emission of phenanthrene crystals, UV excited at liquid N2 temperature, is investigated on the basis of a previously proposed kinetic model. It is found to fit quantitatively the glow peak shape and some evidence is obtained that radiative recombinations take place through a two-step process.

Thermoluminescence of hydroxy and aminobenzoic acids

Abstract The thermoluminescence glow spectra of ortho, meta and para-hydroxy and aminobenzoic acids have been investigated as obtained through UV excitation at low temperature. The trap depths are found to range from 0.13-0.39 eV for the various acids, while the trap density turns out to be highest in the ortho-forms. This feature is ascribed to the poorer stability of the dimers in the ortho-acids, which produces a larger concentration of lattice defects. This conclusion is substantiated by means of different experimental evidences which provide further information on the lattice bonds, such as, for instance, the fundamental absorption energies. A possible interpretation for the thermoluminescent defect structure is suggested.

Thermoluminescence of terphenyl isomers

Abstract The thermoluminescent emissions of terphenyl isomers have been investigated as excited at liquid N 2 temperature by UV radiation. The absorption and excitation spectra have also been determined. The ortho -isomer was found to show an exceedingly pre-eminent thermoluminescent yield, while, on the contrary, its photoluminescent emission turned out to be smaller than those of the meta - and para -isomers. These results are explained by taking into account the steric hindrance between hydrogen atoms which prevents the ortho -isomer from assuming a planar structure. Consequently, the lattice turns out to be less closely bound, so originating a larger concentration of defects able to behave as carrier traps. Arguments are advanced, as well, to understand the nature of these traps, which constitute the centres responsible for the thermoluminescence.

On thermoluminescence build-up in ionic crystals

Thermoluminescence build-up in ionic crystals is studied with a kinetic model utilizing subsidiary conditions from linear nonequilibrium thermodynamics. The equations obtained are successfully applied to CaF2 and KCl excited by soft X-rays at room temperature. The experimental results show the effect of X-ray absorption in the samples.