Deconvolution of optical stimulated luminescence decay curves

The Thermoluminescence (TL)-like presentation method introduced to describe the isothermal decay of a thermoluminescence glow-peak, is extended in the present work for the case of the Optical Stimulated Luminescence (OSL) decay curves. The Glow-Curve Deconvolution analysis extensively used to analyse TL glow-curves is successfully applied to find the individual components of the Optical stimulated decay curves. The method is successfully applied to both synthetic and experimental OSL decay curves of quartz, feldspar and mixed quartz plus feldspar aliquots. The potential use of the Peak Shaped (PS) TL-like presentation to extract qualitative and quantitative information from an OSL decay curves is also discussed.     

Optically stimulated luminescence response of commercial SiO2 optical fiber

The use of Optically Stimulated Luminescence (OSL) for radiation dosimetry has become increasingly popular in recent years. The OSL method is based on luminescence emitted from semiconductor materials stimulated with specific wavelengths of light, after being exposed to ionizing radiation. The OSL intensity is a function of the radiation dose absorbed by the material. This work complements previous studies by the authors of the thermoluminescence (TL) response by SiO₂ commercial optical fiber exposed to ionizing radiation and provides preliminary results describing some of the material’s OSL properties. Linear OSL response to beta-radiation dose, along with a consistent shape of the photon emission curve with time, were observed using a green/blue OSL excitation laser. The reproducibility of OSL response after repeated irradiations and the change in intensity with time were also examined. The search for and characterization of materials that exhibit this OSL response, in parallel with the continued development of OSL methodology and instrumentation, is an important scientific and commercial issue.     

Estimation of confidence intervals in calculation of the distribution of luminescence lifetimes from the kinetics of multiexponential decay

A new approach to the calculation of the luminescence lifetime distribution from experimental luminescence kinetics of multiexponential decay is proposed, which is based on the Tikhonov regularization method with allowance for the estimation of confidence intervals in solving linear inverse problems under the condition of non-negativity of the solution. The proposed approach permits finding solutions with almost optimum degree of smoothness, and analyzing them for the presence of artifacts caused by the ill-posedness of the problem.     

Medium effect on the decay kinetics of benzophenone oxide

The rate constants of benzophenone oxide decay measured at 25°C by flash photolysis (FPh) strongly depend on the nature of the solvent [2k=(2.6±0.3)×10⁷ L mol⁻¹ s⁻¹ in CH₃CN, and (2.0±0.2)×10⁹ L mol⁻¹ s⁻¹ in pentane].     

Preliminary study of the thermally stimulated blue luminescence of ulexite

In this paper, novel results on the blue thermally stimulated luminescence (TSL) emission of ulexite (NaCaB₅O₆(OH)₆·5H₂O) have been studied. The four maxima appearing at 60, 110, 200 and 240°C on the TSL glow curves of this borate could be respectively associated to: (i) the first dehydration (NaCaB₅O₆(OH)₆·5H₂O→NaCaB₅O₆(OH)₆·3H₂O), (ii) the creation-annihilation of the three-hydrated phase, (iii) the Na-coordinated chains dehydroxylation and the starting point of the alkali self-diffusion through the lattice and (iv) the amorphisation of the lattice. These results are fairly well correlated with the differential thermal analyses (DTA), in situ thermal observations under environmental scanning electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques.     

Optically stimulated luminescence dating of pottery from Turkey

In this study, the potential of optically stimulated luminescence (OSL) dating for archaeological potteries was investigated. Firstly, recently purchased OSL and alpha counter systems were calibrated. Then, archaeological sherds taken from Dat?a-Burgaz (Mu?la, Turkey) archaeological site of archaic and classical period (700-400 BC) were dated. Samples were prepared by the fine grain technique and paleodose was found by using the additive dose technique. The annual doses of uranium and thorium were determined by using the alpha counter. The potassium, which has no alpha activity, was determined by atomic absorption spectrometry. The age of the sherds was found to be 2340+/-190 years which is in good agreement with the archaeological evidence involving figurines and coins obtained in the same level.     

Estimation of some parameters of the exchange mechanism of luminescence decay

The rates of variations of the relative yield (α_η) and decay time (α_τ) with the acceptor concentration (C_A) have been calculated in the vicinity of C_A = 0. On the basis of the equations obtained, the ratio α_η/α_τ has been found and a simple scheme of experimental data analysis proposed.     

Thermally stimulated luminescence of a natural layered double hydroxide

Layered double hydroxides (LDHs) and many of the related hydrotalcite-like minerals have been well studied from the chemical and structural point of view; however, their luminescence properties have been scarcely studied. We herein report on the thermoluminescence (TL) behaviour of a natural LDH (Mg₆Cr₂CO₃(OH)₁₆·4H₂O), previously characterized by X-ray fluorescence, X-ray energy-dispersive spectrometry, electron probe microanalysis, thermogravimetry and differential thermal analysis, that exhibited a very complex green-IR spectral emission. The broad waveband peaked at ~?640 nm can be mainly linked to the ⁴T₁?→?⁶A₁ (at 570 nm), ⁴A_2g?→?²E_g (~?685 nm), ⁴T₁?→?⁶A₁ (~?700 nm), and ¹T_2g?→?³A_2g (green) and ¹T_2g?→?³T_2g (red) transitions due, respectively, to the presence of Mn²⁺, Cr³⁺, Fe²⁺ and Ni²⁺. The weak red-TL emission can likely be attributed to the quenching effect due to Fe (~?8–11%) ions substituting for Mg²⁺.     

Influence of triplet—triplet excitation transfer on the decay function of donor luminescence

The triplet—triplet electronic excitation transfer from benzophenone to naphthalene in rigid solutions has been investigated by measuring the non-exponential decay curve of benzophenone photphorescence using a laser pulse for excitation. The results of measurements were satisfactorily reproduced by Inokuti—Hirayama's formula based on Dexter's theory of exchange interaction.     

Alternative determination of equivalent dose by green light emitting diodes optically stimulated luminescence using the unstable luminescence

A new method for the determination of the equivalent dose (ED) in minerals has been developed, based on the unstable part of luminescence which fades away at ambient temperatures. Optical stimulated luminescence employing green light emitting diodes is used in two cases; a reference quartz sample and an archaeological ceramic. In both instances the obtained (ED) with the new technique provides a satisfactory agreement within the expected errors.     

Reasons for the decay of the electrochemical luminescence of rubrene dissolved in benzonitrile

Thin layer cells under direct voltage excitation, coupled with fluorescence spectroscopy, yielded information about the decay of rubrene electrochemical luminescence on prolonged electrolysis. At voltages <2.3 V, about 1/10 of the rubrene in the cell was destroyed through a reaction of the rubrene radical cation and a new electro-active species appeared. At higher voltages, both the radical cations and anions of rubrene were present, the rubrene was destroyed more completely and products that fluoresced in the blue were formed. Further, at voltages >2.5 V, benzonitrile radical anions could be formed. These may replace the rubrene anions in the electrochemical luminescent reaction and complicate the degradation pattern.     

Enzyme kinetics of multiple alternative substrates

An innovative theoretical approach that enables the complete characterisation of enzyme–substrate and enzyme–substrate–competitor reactions is generalised to systems with multiple alternative substrates. Based on the quasi‐steady‐state assumption, time‐dependent closed form solutions are presented for cases with even, weak and mixed substrate competition. The analytic framework should facilitate the development of computational fitting procedures for progress curves, simplifying the measuring process and increasing the reliability of reaction constant estimates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped calcium phosphate

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies on uranium doped calcium phosphate yielded mechanistic information on the observed glow peaks at 365, 410 and 450 K. TSL spectral studies of the glow peaks showed that UO₂ ²⁺ acts as the luminescent center. Electron paramagnetic resonance studies on gamma-irradiated samples revealed that the predominant radiation induced centers are H⁰, PO₄ ^2-, PO₃ ^2- and O^- ion. Studies on the temperature dependence studies of the EPR spectra of samples annealed to different temperatures indicate the role of H⁰ and PO₄ ^2- ions in the main glow peak at 410 K.     

Luminescent decay kinetics of malachite green on a picosecond time scale

Luminescence measurements after laser pulse excitation are reported for the dye malachite green in solutions of different viscosity with a time resolution of 10 ps.     

The interference of fluctuations in the kinetics of metastable state decay

The interference of nucleation-rate fluctuations during metastable state decay has been considered. The effects have been shown to be always weak; therefore, averaged parameters may be used to construct the kinetics of the process.     

Formation and decay kinetics of optically pumped LiMg excimers

A mixture of Li and Mg vapors at 900°C was optically pumped at 488 nm by an Ar⁺ ion laser. The resulting Li₂ fluorescence and LiMg* excimer chemiluminescence intensities were analyzed to determine rate constants for the reactions Li₂(B¹π) + Mg → LiMg* + Li and LiMg* + Li → Li₂(a³π) + Mg and the radiative decay rates of Li₂(B¹π) and LiMg*.     

Fluorescence decay kinetics of acetone vapour at low pressures

Acetone-h₆ and -d₆ were excited by a short UV laser pulse to the nπ* state. Using pressures of 10^?4-10 ^?3 Torr, two distinct decay components were observed - the faster with a decay time of less than 20 ns and the slower of about 5 μs. Increasing the pressure leads to the appearance of two longer-lived decay components, which are apparently absent in the case of isolated molecules. Based on the deuteration effect, excitation wavelength dependence, quenching kinetics and analogy with other molecules, the four decay components are assigned as follows. The fastest component is due to dephasing of the initially excited state, forming a quasi-stationary eigenstate. The second component is due to the radiative decay of the latter states. The third, to decay of triplet states not directly coupled to the initially excited singlet states, and the last to the thermalized triplet state.