Mesomorphic and optical properties of undoped and doped azomethines

Three calamitic azomethines were prepared by the condensation of the benzene-1,4-dicarboxaldehyde with the three aliphatic amines (LCOA1–LCOA3). The structures of the azomethines were characterized by means of FTIR, ¹H, ¹³C NMR spectroscopies and elemental analysis; the results showed an agreement with the proposed structure. The azomethines emitted blue or green light. An influence of n-decyl sulfonic acid (DSA) on mesomorphic behaviors, absorption and emission wavelengths was investigated. The liquid crystalline properties of the azomethines were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide and small angle X-ray diffraction (WAXS and SAXS). The mesomorphic properties of the compounds depend on both the length of the outer flexible spacers and the kind of connection between the alkyl groups and the imine group, i.e. directly via aliphatic chain or by phenyl ring. LCOA1–LCOA2 exhibited smectic and nematic phases, whereas the LCOA3 did not exhibit thermotropic liquid crystal properties. Basing on the comparison of thermal behaviors and optoelectronic properties of undoped (LCOAX) and doped (LCOAX/DSA) azomethines it was shown that ionic self-organized processes are powerful and are able to tune: i) the processability, ii) the LC behavior, and iii) the maximum of emission band of the synthesized azomethines.     

Specific features in the kinetics of thermally stimulated luminescence of α-Al2O3 crystals containing defects

A study of specific features in the kinetics of thermoluminescence (TL) of defective α-Al₂O₃ crystals is reported. The TL properties are experimentally shown to be related to the presence of oxygen vacancies of thermochemical or radiation origin. It is established that the differences in the TL kinetics in α-Al₂O₃ samples grown under different conditions can be accounted for by the hypothesis that the energy spectra of the trapping levels have different widths. As is demonstrated with a titanium impurity, this broadening of the energy spectrum can originate from the presence of traces of native impurities in the α-Al₂O₃ lattice. Fiz. Tverd. Tela (St. Petersburg) 39, 1538–1543 (September 1997)     

Optoelectronic property tailoring of conjugated heterocyclic azomethines – the effect of pyrrole,thiophene and furans

A series of de novo symmetric heterocyclic azomethine dyads and triads consisting uniquely of furans, thiophenes, pyrroles and methyl‐pyrroles were prepared. These were prepared to investigate the effect of various heterocycles and the degree of conjugation on the spectroscopic and electrochemical properties. The crystallographic structures of the symmetric azomethines were also compared with their unsymmetric and heterocyclic and homoaryl counterparts. It was found that for a similar series, bathochromic absorbance and fluorescence shifts occurred when progressing in the order of furan < thiophene < pyrrole ≈ methyl‐pyrrole. The spectroscopic properties of the heterocyclic azomethines were also bathochromically shifted relative to their homoaryl analogues as a result of increased degree of conjugation and electronic effects. The former was in part confirmed by crystallographic studies showing the heterocycles adopted co‐planar and antiparallel arrangements. Although all the compounds studied showed weak fluorescence at room temperature, their fluorescence could be restored at low temperatures, implying deactivation of the singlet excited manifold by bond rotation. Meanwhile, irreversible oxidation was observed for all the azomethines studied and their oxidation potentials were contingent on the heterocycle and number of azomethines, ranging between 0.8 and 1.4 V versus Ag⁺. The irreversible oxidation was due to radical cation cross‐coupling resulting in products with higher degrees of conjugation. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

Thermoluminescence characteristics of inorganically and organically capped ZnS:Cu nanophosphors

ZnS:Cu nanophosphors were prepared by wet chemical methods and characterized by X-ray diffraction (XRD). The typical morphologies of the nanophosphors were investigated by scanning electron microscopy (SEM). The thermoluminescence (TL) properties of inorganically and organically passivated ZnS:Cu nanophosphors were investigated after γ-irradiation using a ⁶⁰Co source at room temperature. The TL glow curve of capped ZnS:Cu showed variation in TL peak and intensity as the capping agent was changed. Amongst the synthesized samples the TL glow curve of SiO₂ capped ZnS:Cu showed the highest TL intensity. It has been found that TL response of SiO₂ capped ZnS:Cu is linear in the range 10-550 Gy. A discussion of the obtained results is also presented.     

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract

We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu²⁺ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu²⁺ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and F_z participation in OSL. These results provide us a supportable correlation between F and F_z as responsible centers for OSL and TL processes.     

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. Fiz. Tverd. Tela (St. Petersburg) 40, 229–234 (February 1998)     

Luminescence properties of Ce-doped oxyorthosilicate nanophosphors and single crystals

In this work we investigate and compare the thermoluminescence (TL) and related luminescent properties of cerium-doped Lu₂SiO₅ (LSO), Gd₂SiO₅ (GSO), and Y₂SiO₅ (YSO) nanophosphors prepared by solution combustion synthesis (SCS) to the properties of their single crystal counterparts. Photoluminescence emission and excitation spectra were obtained for comparison with TL and radioluminescence (RL) emission bands. We then compared the structure and intensity of TL curves, RL intensity, and afterglow at room temperature and investigated the trapped charge stability (revealed by TL). The results showed that the SCS technique is capable of producing scintillating materials with less afterglow and RL output comparable to single crystals. The nanophosphor samples also showed lower TL intensities than their single crystal counterparts, which points to a lower concentration of trapping centers. These results demonstrate the potential of nanophosphors produced by SCS for use as scintillators.     

Luminescence in LiNaSO4:Eu phosphor

Abstract

LiNaSO₄: Eu is a recently discovered thermoluminescence dosimetry (TLD) phosphor which is more sensitive than the widely used CaSO₄:Dy. In this paper results are reported on TL glow curves, TL emission spectra and PL photoluminescence. These measurements help to understand the role of impurity and the mechanism of thermoluminescence in this phosphor.     

Computerized glow curve deconvolution of thermoluminescent emission from polyminerals of Jamaica Mexican flower

The aim of this work is to study the main thermoluminescence (TL) characteristics of the inorganic polyminerals extracted from dehydrated Jamaica flower or roselle (Hibiscus sabdariffa L.) belonging to Malvaceae family of Mexican origin. TL emission properties of the polymineral fraction in powder were studied using the initial rise (IR) method. The complex structure and kinetic parameters of the glow curves have been analysed accurately using the computerized glow curve deconvolution (CGCD) assuming an exponential distribution of trapping levels. The extension of the IR method to the case of a continuous and exponential distribution of traps is reported, such as the derivation of the TL glow curve deconvolution functions for continuous trap distribution. CGCD is performed both in the case of frequency factor, s, temperature independent, and in the case with the s function of temperature.     

Thermoluminescent properties of a Li2O-B2O3-Al2O3 glass system doped with CaF2 and Mn

A Li₂O-B₂O₃-Al₂O₃ glass system doped with CaF₂ and Mn was synthesized by fusion and its physical properties were investigated using thermoluminescence (TL) and differential thermal analysis (DTA) techniques. The TL glow curve peaks, resulting from this analysis, are characteristic of metastable levels intrinsic to CaF₂ crystals that have undergone γ-ray irradiation from a colbalt-60 (⁶⁰Co) source. This provides evidence of CaF₂ crystal formation in the glass system. Furthermore, the TL glow peak at about 480 K was stable at room temperature, sensitive to ⁶⁰Co γ-rays and showed good linearity with doses ranging from 3 Gy to approximately 100 Gy, and consequently could be used to quantify radiation doses. High quality synthesis of these crystals permits control of their thermoluminescent properties.     

Effect of Fe,Co, Ni and Cd CO‒activation on luminescence emission and decay of CaS:Ce phosphors

Cathodoluminescence (CL), photoluminescence (PL), thermoluminescence (TL) spectra, and decay after laser beam excitation of cerium-activated CaS phosphors doped with Fe, Co, Ni or Cd have been investigated. These studies shed some light on the nature of luminescence centres and the association of various groups of traps with the dopants. Effect of concentiation variation of these four elements on emission and decay characteristics of CaS:Ce phosphor has been discussed. In contrast with the earlier publication [W. Lehmann and F. M. Ryan, J. Electrochem. Soc. 119, 275 (1972)] we have found that Ni is an effective killer, Cd ineffective and Co has no clearly observable effect. Fe has also been found to be an effective killer for CaS:Ce phosphors. Ni and Fe appear to be more effective quenchers for shorter wavelength emission band characteristic of Ce in CaS.     

Thermoluminescence dosimetry in evaluation of liquid 32P sources for intravascular brachytherapy

Several new types of miniature (1 and 2 mm diameter) thermoluminescence (TL) detectors were elaborated and tested aiming at dosimetry of liquid [³²P] sodium phosphate sources suggested for intravascular brachytherapy. They were prepared using LiF:Mg,Cu,P and LiF:Mg,Ti TL materials in a two-layer technique with the effective thickness below 0.1 mm. Dosimetric measurements were carried out in tissue-equivalent polymethyl methacrylate (PMMA) phantoms, with TL detectors placed at various distances around angioplasty balloons filled with aqueous solution of Na₂H³²PO₄. Of particular interest was the response of detectors placed at shortest distances from the balloon surface. All types of the TL detectors used in trials showed very good spatial resolution and dose readings were consistent for all detector types, even at the steepest parts of the dose–distance curve. In our opinion, the new TL detectors can be recommended for measurements of dose distribution around liquid radiation sources.     

Improving dosimetric properties of tellurite glasses

Thermoluminscence (TL) properties of quaternary tellurite glass in the form 80(TeO₂)–5(TiO₂)–(15−x)(WO₃)–(x)A_nO_m where A_nO_m=Nb₂O₅, Nd₂O₃, Er₂O₃ and x mol% have been measured. TL main dosimetry peak for each produced glass sample were investigated for ⁶⁰Co gamma rays. Dosimetric properties of the quaternary tellurite glasses have been measured as a function of different compositions of the glass system in different rare earth oxides concentration by using thermoluminescence (TL) detection technique.     

Thermoluminescence, structural and magnetic properties of a Li2O-B2O3-Al2O3 glass system doped with LiF and TiO2

A Li₂O-B₂O₃-Al₂O₃ glass system, un-doped and doped with LiF, and/or TiO₂ was synthesized by the fusion method and its physical properties were investigated by thermoluminescence (TL), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), atomic force microscopy (AFM) and differential thermal analysis (DTA). The samples were subjected to γ-rays from a colbalt-60 (⁶⁰Co) source. These techniques provided evidence of LiF and LiF doped with Ti crystal formation in the glass system. A TL glow peak at about 433 K was sensitive to ⁶⁰Co γ-rays and showed good linearity with doses and consequently could be used to quantify radiation doses.     

Synthesis and thermoluminescence characterization of Na6Mg(SO4)4:RE (RE = Ce,Tb) phosphors

Thermoluminescence (TL) properties of sulfate-based phosphors activated by different rare earths have received tremendous attention to the field of radiation dosimetry. Those TL materials based on CaSO₄ have been widely applied for medical and environmental dosimetry. Taking this fact into account we have synthesized Na₆Mg(SO₄)₄ doped with Ce and Tb by wet chemical method. The prepared phosphor was characterized by XRD, FTIR, photoluminescence (PL) and thermoluminescence. For TL study, the phosphor is irradiated with γ-rays from ⁶⁰Co source. For studying luminescence properties, the prepared phosphor was annealed at different temperatures and effects of these annealing temperatures on Na₆Mg(SO₄)₄ samples are investigated and quantified. The changes in the glow curve and PL emission spectrum are also investigated as a function of annealing temperature and the annealing temperature was optimized. For calculation of trapping parameters various methods such as peak shape (PS) method, initial rise (IR) method, various heating rate (VHR) method, and computerized glow curve deconvolution (CGCD) are employed.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Thermoluminescence properties of rare earth doped lithium magnesium borate phosphors

This paper reports the thermoluminescence (TL) properties of rare earth doped lithium magnesium borate (LMB) polycrystalline phosphor. LMB phosphor has been prepared by high temperature solid state diffusion method. Among all the rare earth doped LMB phosphors, terbium doped material has shown maximum TL sensitivity with a broad dosimetric glow peak at 240 °C. near the tissue equivalent TL phosphor with terbium dopant has about four times the TL sensitivity of TLD-100. The main dosimetric properties such as glow curve stability, TL response versus absorbed dose, post-irradiation storage stability, and reusability are investigated. This TL material has a linear dose response up to 10³ Gy, negligible storage fading and a simple annealing procedure for reuse. The TL emission spectra of LMB:Tb³⁺ showed broad green emission at 544 nm, which merged with host emission. The characteristic Tb³⁺ emissions are seen in the photoluminescence (PL) spectra.     

Effect of gamma irradiation on thermoluminescence and thermodynamic parameters of LiKSO4 doped with Nd2 O3

Abstract

The thermoluminescence and thermo-dynamic parameters of LiKSO₄: Nd were investigated. The effect of Nd dopant concentration in the range 0.1-1% as well as that of γ-irradiation dose in the range 56.3-3.24 × 10⁵ Gy were studied. The glow curves of the material are characterized by a double peak; each behaving seperately with radiation dose. The highest TL enhancement was obtained for Nd concentration of 0.5%; while irradiation dose of few hundreds Gy gave the best TL response. The thermodynamic parameters of LiKSO₄ doped with 0.5% Nd decreased with radiation dose up to about 5000 Gy.     

X-ray induced thermoluminescence in urea

The thermoluminescence (TL) spectrum of X-irradiated urea in the interval between N₂ liquid temperature and room temperature was obtained. Both the “initial rise” and the May and Partridge methods were used for analyzing the three glow peaks which are characteristic of urea, thus obtaining the values of the thermo-ionization energy and the kinetic order of the TL process. A hypothesis for identifying the nature of the defects responsible for the observed glow peaks was made.