R. Aceves

The role of F centres in the thermoluminescence of low-energy UV- and X-irradiated KCl:Eu2+

The thermoluminescence of ultraviolet- (250 nm) and X-ray-irradiated KCl:Eu2+ is investigated. The peaks are located in the same positions independent of the radiation used to excite the sample, with differences only in the peak intensity ratios. Thermal and optical bleaching methods allow us to relate the thermoluminescence peaks located in the low-temperature region (320-425 K) to Fz centres and those in a higher-temperature region (425-530 K) to F centres.

Quantum size effect in the excitonic luminescence of CsPbX3-like quantum dots in CsX (X = Cl, Br) single crystal host

Copyright (c) 1997 Elsevier Science B.V. All rights reserved.Luminescence of CsPbX 3 -like quantum dots in CsX crystal host (X=Cl, Br) is reported. Single band spectrum is found for as grown or heavily annealed (T=240°C) CsX:Pb, while a family of emisssion bands is observed after annealing at temperatures below 210°C. Anisotropic growth of quantum dots in the early stage is proposed and positions of emission peaks are calculated for CsPbCl 3 quantum dots using a simple model.

Dosimetric properties of KCl:Eu2+ under α, β, γ, x ray, and ultraviolet irradiation

The thermoluminescence (TL) characteristics of KCl:Eu2+ subjected to α, β, γ, x ray, and ultraviolet (UV) radiation (200–300 nm), as well as the dose response was investigated. The TL glow curve structure is very similar for any type of irradiation used with differences only in the peak intensities; it has good reproducibility. Also, the dose response is linear for all types of irradiations. These results allowed us to conclude that the KCl:Eu2+ crystals may be used as a dosimeter for ionizing and nonionizing radiation

Actinometric thermoluminescence response of KCl1−xBrx:Eu2+ mixed crystals

Europium‐doped KCl1−xBrx mixed crystals have been studied as a selective ultraviolet (UV) detector material in the actinometric region (200–300 nm). Thermoluminescence glow curves of room‐temperature UV‐irradiated samples were analyzed as a function of composition x and irradiation wavelength. A thermoluminescence enhancement, relative to the pure KCl and KBr end components is found; for 210–300 nm irradiation the KCl40Br60:Eu2+ solid solution presents a significant increase in thermoluminescence efficiency.

Coexistence of the impurity and perturbed exciton levels in the relaxed excited state of CsCl:Pb crystal

Four bands, all attributable to the main lead centres, have been detected in the emission spectrum of CsCl:Pb crystals. Their spectral and kinetic characteristics have been studied from 1.8 K up to 300 K, and the parameters of the corresponding relaxed excited states (RES) are calculated. It has been shown that the new model proposed by us recently for the RES structure of the luminescence centre in CsI:Tl is valid for CsCl:Pb as well. Two ultraviolet emission bands (at 4.0-3.9 eV and 3.55 eV) excited mainly in the A absorption band of centres (4.65 eV) are ascribed to electronic transitions from Jahn-Teller minima of two types of the triplet RES of the ion. The higher-energy band is split into two components due to the presence of a cation vacancy near . Two visible bands (at 2.6 eV and 1.97 eV) are connected to two different off-centre configurations of excitons localized near the ion.

Exciton 4.29 and 3.65 eV luminescence in CsI:Tl and CsI:Pb

The 4.29 and 3.65 eV emission of CsI:Pb crystals has been studied at 4.2 - 300 K under excitation in the exciton as well as in the lead-induced absorption bands. The results have been compared with those obtained for the corresponding emission of CsI:Tl as well as for the emission of the on-centre and the off-centre self-trapped exciton in a pure CsI crystal. It has been found that, unlike the case in CsI:Tl, in CsI:Pb the 4.29 and 3.65 eV emission is excited not only in the exciton bands but also in the absorption bands of electron impurity centres optically created at 4.2 K together with the centres by photons of 5.1 - 4.0 eV energy. In the latter case this emission is of nature. The optical creation of the centres has been confirmed by luminescence polarization and ESR spectrum measurements.

Luminescence of CsPbCl3-like Quantum Dots in CsCl : Pb Crystals

Absorption and luminescence characteristics of CsPbCl3-like quantum dots in as-received as well as in quenched and subsequently annealed CsCl : Pb crystals have been studied with a spectral resolution of 0.2 nm at temperatures 12–300 K. A complicated structure of absorption, emission and excitation spectra has been found and its dependence on the annealing temperature and time duration is examined. The temperature dependences of the intensities, positions and halfwidths of the spectral bands have been measured. An anisotropic quantum dot growth has been proposed for the explanation of the structural character of the spectra and their temperature dependences.

Nonthermoluminescent dosimetry based on the afterglow response of europium‐doped alkali halides

A new nonthermoluminescent dosimetric technique was developed by using the afterglow response characteristic of alkali halide single crystals doped with europium ions. The afterglow luminescence decayed very slowly and its intensity was proportional to the radiation dose. The radiation dose was measured by the time intergration of the afterglow signal in a selected region. This afterglow dosimetry was compared with the conventional thermoluminescent method, by using single crystals of different alkali halides. The results show that the technique is suitable and versatile for ultraviolet and x‐ray radiation dose determination.

Dosimetric characteristics of ultraviolet and x‐ray‐irradiated KBr:Eu2+ thermoluminescence crystals

Thermoluminescence (TL) characteristics of KBr:Eu2+ (150 ppm) previously exposed to ultraviolet (UV) light (200–300 nm) and x‐ray radiation at room temperature have been determined. The TL glow curve of UV‐irradiated samples is composed of six peaks located at 337, 384, 402, 435, 475, and 510 K. The TL glow curves of x‐irradiated samples show mainly a TL peak around 384 K. The TL intensities of UV‐irradiated (402 and 510 K glow peaks) and x‐irradiated specimens present a linear dependence as a function of radiation dose as well as fading stability 300 s after irradiation. These results further enhance the possibilities of using europium‐doped materials in nonionizing (actinic region) and ionizing radiation detection and dosimetry applications.

Composition dependence of glow peak temperature in KCl1-xBrx doped with divalent cations

Thermoluminescence measurements of β-irradiated Eu2+- and Ca2+-doped KCl1−xKBrx solid solutions excited at room temperature have been carried out to identify the effect of composition on the glow peaks. A typical glow peak has been distinguished for each composition. A linear dependence of its temperature on the composition x has been found. These results indicate that for divalent impurity-doped alkali halide solid solutions these glow peak temperatures are mostly dependent on the lattice constant of the host than on the size of the anion or impurity cation.