R. Pérez Salas

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.

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.

SELF-IRRADIATION IN POTASSIUM HALIDE THERMOLUMINESCENT CRYSTALS

A self‐irradiation process has been observed in potassium halide thermoluminescent crystals. The 0.0117% abundance of the radioactive nuclide 40K in natural potassium, with a halflife of 1.28×109 years, is responsible for about 4.9 μGy/h of self‐irradiation dose. The present finding is of importance in relation to the performance and limitations of recently proposed solid state dosimeters based on doped potassium halide crystals.

Relaxed excited states origin and structure in lead-doped caesium bromide

Absorption, emission and excitation spectra, polarization and decay kinetics of luminescence and their temperature dependences have been studied at 4.2-300 K for several CsBr:Pb samples with various lead concentrations. The origin and structure of the relaxed excited states responsible for the 3.33, 2.8 and 2.43 eV emission bands have been discussed. It has been concluded that the relaxed excited state model proposed for Tl + -doped caesium halides and CsCl:Pb is not valid in case of CsBr:Pb. To establish the origin of the relaxed excited states in a CsBr:Pb crystal, the luminescence characteristics of CsBr:Pb have been compared with those reported for Cs 4 PbBr 6 , PbBr 2 and CsPbBr 3 bulk crystals. It has been assumed that owing to a strong interaction between Pb 2+ and Br- ions, the molecular-like states, which are similar to the excited levels of some stable lead-related compounds, are responsible for the luminescence of CsBr: Pb crystals.

Ultraviolet dosimetric properties of α‐Al2O3 crystals

Thermoluminescence (TL) measurements were performed in crystal samples of α‐Al2O3 (TLD 500 K) subjected to UV irradiation in the range of 200–320 nm. The material is very sensitive to UV light and can be considered potentially useful for actinic region dosimetry. The TL glow curve is composed of two glow peaks centered at 58 and 184 °C, respectively. The TL excitation spectrum shows a maximum for 220 nm light.

A simple calibration method for potassium halide thermoluminescence dosimeters

We present a simple calibration method for europium‐doped potassium halide dosimeters. The procedure is based on the self‐irradiation absorbed dose of potassium halide thermoluminescence dosimeters due to the natural content of the radionuclide 40K in potassium halide crystals. In the small dose range of the order of 0.5 mGy, the precision of the proposed method is highly competitive with traditional calibration methods, without the need of artificial radiation sources and rather expensive and sophisticated measurement equipment.