Trust Management II Karabulut, Yücel; Mitchell, John C; Herrmann, Peter ...
2008, 2008-05-18, Letnik:
263
eBook
This book constitutes the refereed proceedings of IFIPTM 2008: Joint iTrust and PST Conferences held in Trondheim, Norway on June 18-20, 2008. The IFIP series publishes state-of-the-art results in ...the sciences and technologies of information and communication. The scope of the series includes: foundations of computer science; software theory and practice; education; computer applications in technology; communication systems; systems modeling and optimization; information systems; computers and society; computer systems technology; security and protection in information processing systems; artificial intelligence; and, human-computer interaction. Proceedings and post-proceedings of refereed international conferences in computer science and interdisciplinary fields are featured. These results often precede journal publication and represent the most current research. The principal aim of the IFIP series is to encourage education and the dissemination and exchange of information about all aspects of computing.
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•La2MoO6 and La2Mo2O9 phosphors doped with Eu and Dy were synthesized by wet chemical method.•Structural and luminescence properties were conducted by XRD, PL and TL.•Optimum doping ...concentration was 2 mol%.•Activation energies were calculated using Peak shape method.
We report a detailed structural analysis and properties of the photoluminescence (PL) and thermoluminescence (TL) spectra of Eu3+ and Dy3+ incorporated into novel La2MoO6 and La2Mo2O9 phosphors synthesized successfully through gel combustion synthesis. The formation of a tetragonal phase and a cubic structure were verified for La2MoO6 and La2Mo2O9 phosphors via X-ray diffraction (XRD) studies. Dy doped samples exhibited blue and green emissions at 480 nm (4F9/2 →6H15/2) and 572 nm (4F9/2 → 6H13/2), and also Eu doped samples showed a sharp emission peaks at 612 and 619 nm (5D0 →7F2) upon 349 nm pulse laser excitation. Peak shape (PS) technique was utilised to determine activation energy, frequency factor and order of kinetics associated with the main glow curves in undoped and Eu and Dy doped samples after X-ray irradiation. The present findings suggest that Eu and Dy incorporated La2MoO6 and La2Mo2O9 phosphors are highly auspicious candidates for applications in solid-state lighting.
In this study, ZnB2O4:xSm3+ (0.01 ≤ x ≤ 0.05 mol) powder phosphors have been synthesized by low temperature chemical synthesis method. The structure and morphological observation of the phosphor ...samples were systematically monitored by X-ray powder diffraction (XRD) and environmental scanning electron microscope (ESEM) coupled to an energy dispersive X-ray spectrometer (EDS). The all diffraction peaks are well assigned to standard data card (PDF#39-1126). Emission properties of the samples were explored using light emission induced by an electron beam (i.e cathodoluminescence, CL) at room temperature (RT). When excited with electron beam, CL spectral measurements of scrutinized phosphors exhibit orange-red luminescence at 572 nm, 606 nm and 658 nm due to various transition from ground state to 6H5/2,6H7/2 and 4G5/2 states, respectively. The transition 4G5/2 → 6H7/2 located at 606 nm can occur as hypersensitive transition having the selection rule ΔJ = ±1. The observed peaks are in the region of yellow reddish light of Sm3+. Experimental results verify that the optimum Sm3+ content in terms of intense luminescence for this series of phosphors was 2%. Beyond 2% of Sm3+ ions concentration, luminescence quenching occurs due to an enhanced probability of the energy transfer from one Sm3+ to another that matches in energy via cross-relaxation and dipole-dipole interactions according to Dexter theory. A suitable energy transfer model between two adjacent Sm3+ ions in the ZnB2O4 phosphors was accomplished by the electric dipole-dipole interaction. The critical transfer distance (Rc) for non-radiative energy transfer was found to be 21.52 Å at 2 mol % Sm3+ doped ZnB2O4. Additionally, thermoluminescence (TL) glow curves of undoped and Sm activated ZnB2O4 under beta irradiation of 10 Gy are also discussed here.
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•ZnB2O4:Dy3+ phosphors were successfully prepared by low temperature chemical synthesis method.•The luminescence properties were studied by different excitation sources.•Phosphors exhibited reddish orange emission under electron beam excitation.•The critical distance and luminescence quenching were investigated.
In this study, we report a detailed analysis of the photoluminescence (PL) and cathodoluminescence (CL) properties of La2CaB10O19 (LCB) doped with Dy ion. Dy doped LCB materials were successfully ...synthesized using a sol-gel combustion method. Dy doped LCB has the monoclinic structure with lattice parameters a = 11.02067 Å, b = 6.55755 Å, c = 9.10541 Å and α = γ = 90.00, and β = 91.49°. Under the excitation by a low voltage electron beam and pulse laser at 349 nm, the LCB:Dy3+ phosphor produces the characteristic emission bands of Dy3+ due to intra-configuration transitions of 4F9/2 → 6H15/2 (480 nm, blue), 4F9/2 → 6H13/2 (574 nm, yellow), 4F9/2 → 6H11/2 (662 nm, red) and 4F9/2 → 6H9/2 (752 nm, red). The concentration quenching phenomenon was observed in both CL and PL measurements and optimum doping concentration was estimated to be 2%. We suggest that the concentration quenching mechanism of intense yellow emission at 574 nm was attributed to dipole-dipole interaction for both CL and PL.
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•Undoped, Dy doped La2CaB10O19 phosphors were successfully prepared via a gel combustion method.•Cathodoluminescence and photoluminescence properties of Dy doped La2CaB10O19 phosphors are reported.•Concentration quenching mechanism of at La2CaB10O19:0.02Dy3+ was discussed.
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•Sm3+ and Dy3+ activated Ca3Al2O6 phosphors are synthesized by gel combustion method using different fuels.•The size of synthesized phosphors is dependent on the utilized fuel ...composition.•Concentration quenching mechanism is discussed according to the Dexter’s theory.•Photoluminescence properties of Sm3+ and Dy3+ activated Ca3Al2O4 phosphors are discussed.
Sm3+ and Dy3+ activated Ca3Al2O6 phosphors were produced through a gel combustion method using Urea + β-Alanine, Urea, and Urea + Glycine as fuels. The crystal structure and the phase purity of the obtained materials were characterized by X-ray powder diffraction (XRD). Ca3Al2O6:Sm3+ phosphor shows characteristic emission lines (565 nm, 602 nm, 649 nm, and 714 nm) in the orange red region assigned to 4G5/2→6HJ (J = 5/2, 7/2, 9/2, 11/2) transitions of Sm3+. The strongest peak is located at 602 nm. Emission spectra of Ca3Al2O6:Dy3+ show that there are two dominant peaks centered at 480 nm and 573 nm emitting blue and yellow light. Optimum doping concentrations of Sm(NO3)3 and Dy(NO3)3 are 0.01 % and 0.03 %, respectively. The concentration quenching mechanism is verified to be a dipole-dipole interaction as the type of energy transfer among Sm3+-Sm3+ and Dy3+-Dy3+ ions. The critical distance is also calculated to be 24.19 Å and 16.77 Å, respectively.
In present work, a series of Eu doped zinc borate, ZnB2O4, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) ...properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB2O4 host lattice are studied for various beta doses ranging from 0.1 to 10 Gy. The high-temperature peak of Eu activated sample located at 192 °C exhibited a linear dose response in the range of 0.1–10 Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB2O4 were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu3+ ions located at 576–710 nm assigned to the 5D0→7FJ (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu3+ ions at 614 nm with transition 5D0→7F2 was reached Eu3+ concentration of 5 mol%; quenching occurred at higher concentrations. Strong emission peak for Eu3+ ions at 614 nm with transition 5D0→7F2 is observed. The CL experimental data indicate that ZnB2O4:Eu3+ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.
The stuffed derivative of the tridymite structure, the oxide BaAl2O4 has been regarded as a long persistent phosphor. Thermoluminescence (TL) glow curve peaks of thin pellet samples of undoped and, ...Sm3+ and Tb3+ doped BaAl2O4 prepared by combustion method was reported. The structure of the compounds was monitored by X-ray diffraction and found a single-phase compound with a hexagonal structure. Performing a series of TL measurements for the temperature range from room temperature to 400 °C, the effect of beta radiation dose on TL response, various TL heating rate (HR) properties of undoped and Sm3+ and Tb3+ doped BaAl2O4 phosphors were investigated. Peak shape method was also utilized to assess the trap parameters. The activation energy of the main peak at 128 °C was found to be 0.97 eV. TL glow curves obtained from undoped and Tb3+ doped BaAl2O4 decrease with increasing HR value (varying from 0.5 to 15 °C s−1) in a way matching with thermal quenching effect. Contrary to expectations, anomalous HR dependence was observed on Sm3+ doped BaAl2O4 sample and a semi-localized transition model has been used in order to explain such behaviour.
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•Undoped, Tb and Sm doped BaAl2O4 phosphors were successfully prepared by solid state reaction method.•Thermoluminescence of undoped, Tb and Sm doped BaAl2O4 phosphors are reported.•Anomalous heating rate dependence was observed on Sm3+ doped BaAl2O4 sample.•The TL of Tb doped BaAl2O4 is affected by thermal quenching with activation energy 0.97 eV.
Ce doped Yttrium aluminate modified by replacing different molar part of aluminium or gallium (Y3Al5−xGaxO12) and Yttrium silicate phosphors activated with Ce and Tb (Y2SiO5:Ce3+,Tb3+) were ...synthesized by solid state reaction and a gel combustion method, respectively. X-ray diffraction and Scanning electron microscope (SEM) techniques are used to identify their structures and morphologies. Luminescence characteristics are measured and spectroscopic data confirm that Y2SiO5:Ce3+, Tb3+ phosphors can be effectively excited upon UV excitation light and X-ray irradiation, resulting in intense blue and green emissions, respectively. This energy transfer takes place by means of a non-radiative process inside Ce3+-Tb3+ clusters formed in the host matrix. Tb3+ doped Y2SiO5 yields both blue emission 5D3 → 7Fj (j = 3,4,5,6) and green emission 5D4 → 7FJ (J = 3,4,5,6) of Tb3+. Y3Al5−xGaxO12:Ce3+ phosphors exhibit a broad blue emission band originating from allowed 5d-4f transition of the Ce3+ ions under different excitation sources but the broad emission band shifts with increasing of Ga3+ content. This work presents a quantitative understanding of host material's on dopant's luminescence properties and thereby provides an optimization guideline, which is extremely demanding for the development of new luminescent materials.
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•Preparation of YAG:Ce3+,Ga3+ and Y2SiO5:Ce3+,Tb3+ phosphors by a solid state reaction and a gel combustion method, respectively.•The shape and size of phosphor particles were investigated.•The luminescence properties were studied by different excitation sources.•The energy transfer process between Ce3+ and Tb3+ was investigated in YSO host.
Cerium and terbium activated white emitting yttrium silicate phosphors (Y2−x−yCexTbySiO5) having average size between 96 and 123 nm were synthesised by a gel-combustion, and their phase and crystal ...structures, morphologies and ultraviolet (UV)-visible spectroscopic properties were studied. All rare earth doped yttrium silicate (YSO) phosphors are well crystallized powders containing only monoclinic X2-Y2SiO5 phase. No significant changes in the cell parameters were observed with increasing of Tb amount as ionic radii of Tb3+ (0.923 Å) and Y3+ (0.9 Å) have almost the same. Under different excitations, YSO:Ce3+ exhibits blue emission due to the 5d–4f transitions of Ce3+ ions. The series of emission states at different wavelengths of YSO:Tb3+ associated to f–f transition of Tb3+ ion were detected from luminescence measurements. The emission observed at 544 nm (green) corresponding to 5D4 → 7F5 of Tb3+ is strongest one. Incorporation of variable amounts of Tb3+ in the YSO host lattice determines the modification of emission colour from blue through light blue and eventually to bluish green. A possible energy transfer mechanism taking place from Ce3+ to Tb3+ was also discussed in terms of excitation and emission spectra.
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•We present preparation of YSO:Ce,Tb phosphors by a gel combustion method.•The luminescence properties were studied by different excitation sources.•The energy transfer process between Ce3+ and Tb3+ was investigated in YSO host.•The emission could be tunable by both doping concentration of Tb and excitation wavelength.
•ZnB2O4:Dy3+ phosphors were successfully prepared by nitric acid method.•The thermoluminescence properties were studied using beta excitation source.•Trapping parameters were determined using ...different methods.
The intention of this study is to explore the thermoluminescence (TL) behavior of beta irradiated 5% Dy3+ doped zinc borate (Zn(BO2)2:0.05Dy3+) phosphor prepared using the nitric acid method. The TL glow curve corresponding from 1 Gy to 80 Gy beta irradiation (preheated at 140 °C) shows a maxima at c.a. 180 °C. The dependence of heating rate was tested and found out that thermal quenching effect was dominating on TL glow curves as the heating rate increases. The dose response of the phosphor material exposed to beta radiation was investigated. Deconvolution was applied using the peak fit method on the glow curve for optimized conditions. Also peak shape (PS), various heating rates (VHR) and computerized glow curve deconvolution (CGCD) methods were used to evaluate the trapping level parameters, namely trap depth (E), frequency factor (s) and order of kinetics (b) associated with the main glow curve in Zn(BO2)2:0.05Dy3+ phosphor after beta irradiation of 20 Gy. The values of trap depth corresponding with the TL glow peak at 180 °C were found to be 0.93 eV, 0.92 ± 0.05 and 1.05 ± 0.02 respectively. Furthermore W and c parameters characterizing thermal quenching based on the Mott-Seitz theory were determined as 0.31 ± 0.04 eV and 162.55. The TL mechanism appears more likely to get second order kinetics, suggesting the probability of re-trapping of charge carriers by emptied traps.
