Thermostimulated Luminescence Research Articles

Stimulated luminescence and photo-gated hole burning in BaFCl 0.8Br 0.2:Sm 2+,Sm 3+ phosphors

The photo- and thermo-stimulated luminescence (PSL and TSL) of BaFCl 0.8Br 0.2:Sm 2+,Sm 3+ phosphors were investigated. It is found that the stimulated luminescence intensity of Sm 2+ is almost equal to that of Sm 3+ even if the content of Sm 2+ is much lower than that of Sm 3+. Only the stimulated luminescence of Sm 2+ is observed in the sample in which the content of Sm 2+ is much higher than Sm 3+, demonstrating that the PSL or TSL efficiency of Sm 2+ is much higher than that of Sm 3+. This is attributed to the effective overlap of the e–h emission with the absorption of Sm 2+ centers which may make the energy transfer from the electron–hole pairs to Sm 2+ effectively. In BaFCl 0.8Br 0.2:Sm 2+,Sm 3+ the stimulated luminescence is considered to be occurred via the recombination of photoreleased electrons with the [Sm 2++h] or [Sm 3++h] complex and the energy transfer from the electron–hole pairs to the luminescence centers (Sm 2+ and Sm 3+) is concerned to be the major step to determine the stimulated luminescence efficiency. The X-ray-induced stimulated luminescence is compared and connected to the photon-gated hole burning. The net result of the two processes is quite similar and may be comparable. It is suggested from the observations of stimulated luminescence that electron migration between Sm 2+ and Sm 3+ is not the major process, color centers may play an important role in hole burning. The information from stimulated luminescence is helpful for the understanding of the hole burning mechanism.

Biological control of malaria vectors by locally produced primary powder of bacillus thuringiensis serotype H-14 in Iran.

Modern scientific investigations of scintillation characteristics in new materials make high demands to experimental set-ups. For any in-depth study of new materials complex experimental devices are needed. In this work, we present our experimental complex for studying the main scintillation properties of luminescent materials. As an object of investigation for a demonstration of this set-up possibilities the Pr-doped phosphors have been chosen.The developed device allows us to hold the following measurements: emission spectra, kinetics, relative light output under steady state and pulsed X-ray excitations, thermo-stimulated luminescence and afterglow. Some new results in the Pr-doped phosphors’ luminescent characteristic investigations which have been obtained via this facilities are presented in this paper.

On the luminescence of TlCdI 3 crystal

Optical-spectroscopy and spectral-kinetic parameter measurements of a perovskite-like TlCdI 3 crystal have been performed in the temperature range of 77–300 K. Exciting in the exciton absorption band ( E n =3.057 eV, n=1) at 77 K, the photoluminescence (PL) spectrum has two Gaussian shaped emission bands: a narrow band at 2.868 eV ( I) and a broad band at 2.370 eV ( II). The presence of a separate TlI phase is easily identified by means of 2.125 and 2.524 eV emission bands. The PL band I characterized by a 2.5 ns decay time is attributed to the cation bound exciton, and the PL band II is assigned to the anion self-trapped exciton. The latter band comprises the fast as well as the slow decay components. Their decay times at 77 K are: τ f=3.7 ns and t s=2.20 μs respectively. The thermal dependence of the latter permits the determination of the activation energy for nonradiative transitions (80.6 meV). The absolute luminescence light output for both PL bands abruptly diminishes when the temperature increases. In the case of X-ray excitation, the spectral position of the luminescence band has a strong dependence on foreign impurities. Excited by X-rays at 77 K, the TlCdI 3 crystal does not provide so many defect centers. Trap depths (0.26 and 0.34 eV) were obtained from the thermostimulated luminescence data.

A critique on the Ce to Mn energy transfer and sensitization of thermostimulated luminescence in CaSO 4:Ce,Mn

A critique on the Ce to Mn energy transfer and sensitization of thermostimulated luminescence in CaSO 4:Ce,Mn

UV-dosimetric material based on KMgF3 perovskite

It is shown that KMgF3(Eu) crystals efficiently store energy from 250–320nm UV irradiation (the wavelength range most dangerous for health). The composition of anion and cation dopant determines both the intensity and the spectra of the thermostimulated luminescence. The mechanism of energy storage resulting from UV irradiation with energy lower than the band gap is proposed.

Photo- and thermo-stimulated luminescence of CsI—Tl crystal after UV light irradiation at 80 K

Thermo- and photo-stimulated luminescence are studied for CsI—Tl crystal after the irradiation with the UV light at 80 K. Creation spectrum of the photostimulated luminescence coincides with the D absorption band of Tl+ ions. Nature of the defects created by UV light at low temperatures is discussed basing on the correspondence between the thermostimulated glow curve peaks and thermal evolution of the photostimulation spectra observed after irradiation in the D absorption band. Three bands at 1400, 950 and 580 nm have been observed in the stimulation spectrum at 80 K. The 1400 and 950 nm stimulation bands are presumably explained as the optical transitions in the Tl0 centre forming the spatially correlated defect pair with Vk centre while the 580 nm stimulation band is connected with the unperturbed Tl0 centres. It is concluded that the Tl+ luminescence at low temperature is connected with the electron recombination with the Tl2+ centre.

Caracterisation des Solides par Thermoluminescence

The thermoluminescence method (TL), or the thermostimulated luminescence is one of the techniques which correlate thermal and optical methods and usually used to characterize the defects occurring in insulating or semiconductor materials. After a brief description of the TL phenomenon based on the example of α-alumine, we present some applications of thermoluminescence.

Interactive process in the mechanism of thermostimulated luminescence in anion-defect α-Al2O3 crystals

A study of the role of deep traps in the specific features of the thermoluminescence (TL) of anion-defect α-Al2O3 single crystals is reported. The existence of deep traps is proven by direct observation of the associated TL peaks. Experimental support for the effect of deep-trap filling on the main characteristics of the main TL peak at 450 K is presented. A model involving trap interaction is proposed, which differs radically from the others described in the literature by taking into account the temperature dependence of the carrier capture probability by deep traps. This model was used to calculate the dependences on heating rate and deep-trap filling of the main parameters of the main TL peak for the crystals under study (TL yield, glow-curve shape, and sensitivity to the stored light sum), which were found to be close to those observed experimentally.

A comment on 'The effective electron affinity estimation from the simultaneous detection of thermally stimulated luminescence and exoelectronic emission. Application to an -alumina single crystal'

R Bindi et al published recently a paper presenting a method of estimation of the electron affinity from the simultaneously measured thermostimulated luminescence and exoelectron emission graphs. The method is quite promising, but the results permit an alternative interpretation via field-assisted emission, suggested in the comment. Some conceivable ways of overcoming this ambiguity are also pointed out.

The absorption spectrum of radiation-colored SrCl2-Ce crystals

We investigate the spectra of the x-ray radiation-induced absorption of SrCl2−Ce crystals over the spectral range 345–830 nm and their temperature transformations in the interval from 77 to 450 K. We found that radiative color centers are characterized by a complex spectrum of induced absorption that contains wide bands of photochromic PC (750, 519, 378 nm) and PC+ (620, 446, 340 nm) centers and quasi-linear bands of Ce2+ centers. The most significant thermal transformations of radiative color centers occur in the vicinity of the thermostimulated luminescence peak of 394 K, at which the holes of the PC+ centers recombine with the electrons of the Ce2+ centers.

Nature of the blue luminescence bands in PbWO 4

The photoluminescence spectrum of PbWO 4 is composed of blue and green bands, previously attributed to the regular WO 4 group and to the defect-related WO 3 group, respectively. Untill now only green emission was observed in the thermostimulated luminescence (TSL) above 77 K. Investigation of the TSL spectra starting from 20 K indicates that the blue band, being definitely present at least in the 28 K TSL peak, is also due to recombination emission at defect sites.

Luminescence properties of KNbO 3 crystals

Thermostimulated luminescence, X-ray-induced luminescence, photostimulated luminescence as well as the time-resolved luminescence and absorption after pulsed electron beam irradiation were studied in KNbO 3 crystals at 80–400 K. A correlation between defects causing the luminescence and blue-light-induced IR absorption effects supressing the second harmonic generation efficiency in KNbO 3 is discussed.

Colour centres in LiBaF 3

The X-ray-induced optical absorption (OA) and the spectra of magnetic circular dichroism (MCD) followed by optically detected EPR (ODEPR) have been investigated in undoped LiBaF 3 crystals. According to ODEPR, the absorption bands in the spectral region 470–770 nm correspond to the F-type centres, whereas the absorption band at 420 nm is assigned to the hole centres. The redistribution of electrons to the thermal more stable F-type centres indicates that all types of colour centres are annealed in the course of the thermal release of electrons from F-type centres, accompanied by a thermostimulated luminescence.

Detecting media for combined ESR-TSL-TSEE dosimetry

Some new and known materials are studied by methods of electron spin resonance (ESR), nuclear magnetic resonance (NMR), thermostimulated luminescence (TSL) and thermostimulated exoelectronemission (TSEE), in order to evaluate the possibility of their application as detecting media in solid state dosimetry.

Low temperature optical spectroscopy of nonlinear BBO crystals

The absorption reflection and luminescence excitation spectra, as well as the x-ray excited stationary and thermostimulated luminescence spectra of BBO crystals have been measured over a wide spectral (4–30 eV) and temperature (8–300 K) range. The experimental data show that the formation of the absorption edge of the crystal is strongly affected by excitonic-type excitations.

Two-stage photoexcitation of thermo-stimulated luminescence in CaSO4

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The Possibility of a Combined Detector for Ionising Radiation

Experimental investigations of the possibilities of a combined detector for ionising radiation using synchronous measurements of thermostimulated exoelectron emission (TSE) and luminescence (TSL) are described. The investigations were carried out on monocrystalline aluminium oxide irradiated by X rays and gamma radiation.

Luminescence Properties of Transparent BeO:Li Ceramics

The results are presented of an investigation of radioluminescence and phosphorescence spectra, decay of phosphorescence at a constant temperature, and thermostimulated luminescence of transparent BeO:Li ceramics. The phosphorescence decay dependence on time suggests the appearance of tunnelling.

Simultaneous Detection of Thermostimulated Luminescence and Exoelectronic Emission Between 77 and 650 K: Application to Alpha Alumina

Detection apparatus which allows the simultaneous recording of TL and TSEE curves up to 650 K after X or UV irradiations at 77 K is described. Various samples of a-alumina were studied in these conditions. It is shown that this approach avoids some measurement errors and compares accurately the TL and TSEE peaks related to the same trapping centre.

UV emissions in the thermostimulated luminescence of CaSO4: Dy3+. Influence of the host CaSO4 lattice, Dy3+ concentration, and Tm3+ codoping

A double origin of UV emissions in the thermostimulated luminescence (TSL) of CaSO4: DY is discussed: Tm traces and/or lattice emission (SO4 groups). Two types of crystals are compared: a commercial dosimetric powder and our synthesized samples. The effects of the Dy concentration and the Dy/Tm codoping are studied. Une double origine des émissions UV observées dans la luminescence thermostimulée (TSL) du CaSO4: Dy est discutée: présence de Tm et/ou émission de réseau (groupements SO4). Un produit commercial dosimétrique est comparé avec des produits que nous avons synthétisés. Les effets de la concentration de Dy et d'un codopage Dy/Tm ont été analysés.