Investigation on CaF2 lattice defects by thermoluminescence experiments

Brovetto, P.; Delunas, A.; Floris, Andrea; Maxia, V.; Murgia, Martina Salvatorina; Spano, G.

doi:10.1007/bf02451265

Cited by 5 publications

(6 citation statements)

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“…This fact, which explains the variability observed in the TL emission features, is probably a general property of lattice defects, because, when studying other ionic crystal, i.e. A120s and Ca F12, the same situation was met with [4][5][6].…”

Section: -Experimentsmentioning

confidence: 84%

“…Figures 9 and 10 clearly show such an effect. In reality, this represents a sharp difference as regards the TL emission of A12Os and Ca F12 in which precisely the same wavelengths were emitted at increasing temperatures [4,6]. The proposed interpretation assumes the existence of intermediate levels at which electrons are captured before undergoing tunnel recombination with trapped holes.…”

Section: -Experimentsmentioning

confidence: 90%

“…On the other hand, since the wavelenghts of 455 and 500 nm correspond to the photon energies of 2.725 and 2.480 eV, respectively, eq. (5) allows us to write 1) eV (6) 2.725 -2.480 = rl r2 "…”

Section: ) B = Al P(~) +P(o'mentioning

confidence: 99%

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A study of KCL lattice defects by thermoluminescence experiments

et al. 1991

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Summary. --The thermoluminescent emission of X-irradiated potassium chloride is recorded simultaneously vs. temperature and wavelength. Samples of different origin and prepared through different processes, including thermal treatments, are examined. Most records show essentially two glow peaks, the wavelength of the one at higher temperature being slightly shifted toward the red. On the whole, experimental results suggest that luminescent centres are originated by potassium ion vacancies lying at a variable distance from interstitial potassium ions. The observed red shift is ascribed to the Coulomb energy of the pairs of these point defects of opposite charges. PACS 78.60.Kn -Thermoluminescence. PACS 61.70.Ey -Defects in crystals.

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Section: -Experimentsmentioning

confidence: 84%

Section: -Experimentsmentioning

confidence: 90%

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A study of KCL lattice defects by thermoluminescence experiments

et al. 1991

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“…Indeed, CaF2 showed emissions at 459 and 607 nm attributable to recombinations of conduction band electrons with holes bound in H centres and VF centres, respectively [5]. Likewise, the presence of recombination levels attributable to H and VF centres was observed in the TL emission of NaC1 [6] and KC1 [7].…”

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confidence: 96%

A study of lattice defects in alkali fluorides by thermoluminescence experiments

et al. 1993

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Summary. --Lattice defects in KF, NaF and LiF are investigated by recording the thermoluminescent emission of X-irradiated samples vs. temperature and wavelength. Experimental results show the presence of cation vacancies and interstitials in KF and NaF and of F (-) vacancies and interstitials in NaF and LiF. In NaF, the ionization energy of VF centres is found to be 6.4 eV, that of H centres 5.6 eV.PACS 78.60.Kn -Thermoluminescence. PACS 61.70.Ey -Other point defects.1. -Introduction.In alkali halides, lattice defects such as vacancies or interstitials localize point charges of both signs which, when crystals are excited at low temperature by X-rays, trap opposite-sign carriers. The thermoluminescent (TL) emission, originated by carrier recombination when crystals are heated, can be utilized to gain information on the presence and nature of these defects [I].On this basis, we recorded the TL emission of KF, NaF and LiF crystals by means of an apparatus operating under a vacuum and capable of spectral resolution within the 375 to 730 nm range [2]. Samples of high purity were utilized to avoid spurious emissions due to chemical impurities. The effect of thermal treatments, up to the crystal melting point, was also investigated since the nature and density of lattice defects, owing to thermodynamic constraints, are affected by temperature. -Experiments.Samples of LiF were supplied by Koch-Light (purity 99.5%) and J. Matthey (purity 99.98%), those of NaF by C. Erba (purity 99.72%) and J. Matthey (purity 99.999%). As for KF, only samples supplied by J. Matthey (purity 98%) were considered, since this material is highly deliquescent, so that only powders with 903

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“…In this way, separated couples of vacancies and interstitials bearing two opposite-sign electron charges are introduced in the lattice. Such kinds of crystal defects have already been considered in connection with the TL emission of CaF2 [1]. As to the continuous spectrum, it can be ascribed to the recombination of excitons bound to Frenkel defects originated by the displacement in interstitial positions of fluorine F-ions [2].…”

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On the radioluminescent emission of BaF2

1996

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Summary. --The luminescence of barium fluoride excited by X-rays has been recorded vs. wavelength. The spectrum shows two components due to recombination of excitons bound to Frenkel defects and to luminescent centres also active in the thermoluminescent process. The results are interpreted by means of a model based on the Prener and Williams recombination scheme.PACS 78.60 -Luminescence and radiative recombination. PACS 71.35 -Excitations and related phenomena.Samples of polycrystalline barium fluoride, BaF2, excited at room temperature (295 K) with soft X-rays (Cu Ka), showed a radioluminescent (RL) emission in the form of a continuous spectrum of intensity decreasing from 380 nm to 600 nm, followed by a broad band at 659 nm. A second very faint band at about 420 nm is barely visible (see fig. 1). These samples, when heated from room temperature to about 700 K at a rate of one K/s, originated a thermoluminescent (TL) emission in which no continuous spectrum was detectable, but a clear glow peak was present with a maximum at about 400 K and 660 nm (see fig. 2). This peak corresponds to the 659 nm band of the RL spectrum. The emissions observed imply the existence in BaF2 of deep trapping levels active in the TL process, accompanied by levels unable to store carriers when the ionizing X-ray flux is interrupted.To explain these results, we have to consider the actual structure of BaF2. In its crystal cell, like in the fluorite CaF2 cell, eight equivalent positions exist in which Ba + § ions can be held. Since the cell contains only four Ba + + ions, room is available for interstitials. On this ground, the most probable origin of the traps responsible for the TL emission is merely the displacement of Ba + § ions in interstitial positions lying in cells placed at a distance from the initial ion positions. In this way, separated couples of vacancies and interstitials bearing two opposite-sign electron charges are introduced in the lattice. Such kinds of crystal defects have already been considered in connection with the TL emission of CaF2 [1]. As to the continuous spectrum, it can be ascribed to the recombination of excitons bound to Frenkel defects originated by the displacement in interstitial positions of fluorine F-ions [2]. In other words, an electron and a hole are captured by a fluorine ion vacancy and an interstitial fluorine producing F-and H-centres, respectively. Recombinations of the nearest F-H pairs give rise to 1107

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Investigation on CaF2 lattice defects by thermoluminescence experiments

Cited by 5 publications

References 8 publications

A study of KCL lattice defects by thermoluminescence experiments

A study of KCL lattice defects by thermoluminescence experiments

A study of lattice defects in alkali fluorides by thermoluminescence experiments

On the radioluminescent emission of BaF2

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