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Öğe Cathodoluminescence emission spectra of Nd-Doped CaF2(1994) Can N.; Kazanci N.; Townsend P.D.; Chadwick A.V.Rare-earth doping of CaF2 results in material which exhibits significant cathodoluminescence (CL) signals. Therefore CL measurements made on CaF2:Nd are reported for the temperature range 50 to 300 K with different excitation modulation frequencies. Since annealing treatment can be used to modify the spectra, the effects of annealing treatments of CaF2: Nd have been examined. Dopant levels used in the present study are 1.0, 0.1, and 0.01% Nd. All dopant levels exhibited different CL spectra with a combination of broad emission bands from the CaF2 host and lines from the Nd dopants. Broad bands are centred near 340 and 645 nm. The intense emission lines at 360, 389, and 419 are assigned to Nd transitions from 4D3/2 to 4Ij (j = 9/2 and 11/2) and 2P1/2 to 4I9/2, respectively. Other transitions from 4D3/2, 4G9/2, 4G7/2 and 4G5/2, 2G7/2 to 4Ij (j = 9/2 to 15/2) are found. The 340 nm band is associated with the intrinsic emission, self-trapped exciton (STE) emission, of CaF2. The temperature dependence of the intensity of the emission band is discussed. The intrinsic emission band intensities decrease with increasing Nd content. Copyright © 1994 WILEY-VCH Verlag GmbH & Co. KGaAÖğe Cathodoluminescence response from rare earth doped Bi4Ge 3O12(Elsevier B.V., 2009) Kibar R.; Çetin A.; Tuncer Y.; Uysal S.; Townsend P.D.; Canimoglu A.; Karali T.; Can N.Room and low temperature cathodoluminescence (CL) of rare earth doped Bi4Ge3O12 (BGO) has been recorded. Luminescence signals noted in the wavelength range (300 - 800 nm) include intrinsic broad emission bands and signals related to Eu3+, Nd3+, and Tm3+. CL measurements made on Bi4Ge3O 12 (BGO) doped with rare earth ions are reported for the temperature range 40 to 300 K with different CL excitation modulation frequencies. Dopant levels used in the present study are 1.1, 0.4, and 0.3 wt% Nd, 0.4 wt% Tm and 3 ppm Eu. All dopant levels exhibited different CL spectra with evidence for lines due to the rare-earth dopants intra-4f transitions. The temperature dependence of the intensity of the emission band is discussed.Öğe Cathodoluminescene of fullerene C60(IOP, Bristol, United Kingdom, 2000) Rowlands A.P.; Karali T.; Terrones M.; Grobert N.; Townsend P.D.; Kordatos K.Fullerenes are not automatic candidates for luminescence analyses due to their highly absorptive nature. Consequently, very few luminescence experiments have been performed on fullerenes. This paper focuses on the luminescence properties of commercially available C60 when bombarded by electrons (cathodoluminescence) and, to a lesser extent, x-rays (radio-thermoluminescence) between 20 and 270 K. Wavelength resolved luminescence signals have been recorded as a function of temperature. CL experiments reveal pronounced anomalies that truncate the emission spectrum between 155 and 170 K. Other less pronounced anomalous features are detected at 70 and 245 K. These dramatic changes in the luminescence spectra are cautiously interpreted to be manifestations of phase transitions and support the view that cathodoluminescence (CL) can be used to monitor for phase transitions in fullerenes. The luminescence signals offer information on the mechanisms of the relaxation processes, including changes in charge trapping energies and emission spectra.Öğe Influence of pulsed laser annealing on rare earth implanted luminescence(Elsevier, 1996) Can N.; Townsend P.D.; Hole D.E.; Ballesteros J.M.; Afonso C.N.; Snelling H.V.Sapphire (Al2O3) and silica samples have been implanted with 400 keV Eu ions at fluences up to 1 X 1016 ions · cm-2. After the samples implanted with Eu ions had been annealed with pulsed excimer lasers it was found that cathodoluminescence (CL) emission intensity of the implanted europium ions was considerably enhanced (i.e. by factors of up to 100 for sapphire and silica at the dose of 1 X 1016 ions · cm-2). Results from furnace annealing of Eu implanted samples, followed by pulsed excimer laser annealing are compared, and the future potential of the method is discussed. The lifetimes range from 6 to about 16 ms and from 0.14 to 1.6 ms for the silica and sapphire samples, respectively, depending on annealing treatment and Eu concentration. Rutherford backscattering spectrometry (RBS) did not show measurable diffusion for the implanted ions.Öğe Ion beam analysis of float glass surface composition(Elsevier, 1997) Lamouroux F.; Can N.; Townsend P.D.; Farmery B.W.; Hole D.E.Data are reported on ion beam surface analysis methods of proton-induced X-ray emission (PIXE), and helium-induced X-ray emission (HIXE), made simultaneously with Rutherford backscattering spectrometry (RBS), which were taken with samples from across the full width of a float glass production line. Data are given for both clear and green glass. Significant variations are recorded between signals from the lower surface, (the face in contact with tin), and the upper surface, not only for the uptake of the tin, but also for the consequent changes in the near surface composition of the other main elements of the glass. In particular, the tin alters the local compositions of iron, calcium, silicon, and sodium. The changes are interpreted in terms of the furnace temperature gradients and chemical interactions. In all cases, including the green glass, iron is depleted from the non-tin face relative to the bulk composition, and the changes of surface content of the iron differs on the two faces relative to the bulk value.Öğe Optical properties and luminescence of metallic nanoclusters in ZnO:Cu(2005) Karali T.; Can N.; Valberg L.; Stepanov A.L.; Townsend P.D.; Buchal Ch.; Ganeev R.A.; Ryasnyansky A.I.; Belik H.G.; Jessett M.L.; Ong C.Copper nanoparticles have been formed in a zinc oxide (ZnO) substrate by Cu implantation at 160 keV. The implant layer shows amorphised behaviour as monitored by the RBS data and optical absorption indicates the surface plasmon resonance peak characteristic of copper nanoparticles. There is nonlinear optical absorption from the Cu nanoparticles. There are numerous changes in the luminescence responses which include a variety of green and yellow emission bands. During excitation there were changes in the cathodoluminescence intensity and lifetime influenced by the surface events, including some unusual features, which may be considered in terms of interactions with surface water and ice. Radioluminescence signals oscillate between the normal emission bands and the wide red line emission from free Zn. Overall ZnO is, therefore, an unexpectedly interesting host for dispersed Cu nanoparticles, not least because the optical features may be compatible with the semiconductor aspects of ZnO. © 2005 Elsevier B.V. All rights reserved.Öğe Optical properties of Tb implantation into ZnO(2007) Çetin A.; Kibar R.; Ayvacikli M.; Tuncer Y.; Buchal Ch.; Townsend P.D.; Karali T.; Selvi S.; Can N.ZnO [0001] single crystals were implanted at room temperature with 400 keV Tb+ ions at fluences in the range of 1 × 1016-2 × 1017 ions/cm2. Zinc oxide was chosen because of its potential for photonic applications as a semiconductor with high radiation resistance. After implantation and post-irradiation annealing, optical absorption was measured in a UV-VIS-NIR range and radioluminescence spectra were recorded at room temperature. Emission signals were generated by the Tb+ ion implants and intrinsic emission of the ZnO matrix were observed. The implant signal intensities were comparable with the host radioluminescence, even though the implants modify the surface of the crystal. It is suggested that the presence of Tb at high concentration generates stresses which influence the bulk material and also potentially forms precipitates or nanoparticles in the near surface region. Overall ion implantation of ZnO results in strongly modified luminescence. © 2007.Öğe Rare-earth-size effects on the thermoluminescence and second-harmonic generation(2001) Townsend P.D.; Jazmati A.K.; Karali T.; Maghrabi M.; Raymond S.G.; Yang B.The substitution of rare-earth ions into insulating host crystals introduces lattice strains and, for non-trivalent sites, a need for charge compensation. Such effects alter the site symmetry and this is reflected in properties such as the wavelength, linewidth, lifetime and relative intensity of the rare-earth transitions. Equally clear, but less well documented, is the influence on second-harmonic generation (even from cubic crystal lattices). For example, in bismuth germanate, second-harmonic generation efficiency varies by factors of more than 100 as a result of different rare-earth dopant ions. The ions are variously incorporated as substitutional ions, pairs, clusters, or even as precipitates of new phases, but the detailed modelling is often speculative. This article summarizes some recent studies which explore the role of rare-earth ions in thermoluminescence and second-harmonic generation. There are numerous differences in glow peak temperature, for nominally the same defect sites, which are thought to indicate charge trapping and recombination within coupled defect sites, or within a large complex. Size and cluster effects can be modified by heat treatments. This review considers the similarity and trends seen between numerous host lattices which are doped with rare-earth ions. For thermoluminescence there are trends in the variation in glow peak temperature with ion size, with movements of 20 to 50 K. Examples are seen in many hosts with extreme effects being suggested for zircon, with peak shifts of 200 K (probably from precipitate phases).Öğe Thermoluminescence studies of LiF: Mg, Ti between 100 and 300 K(2004) Yazici A.N.; Karali T.; Townsend P.D.; Ari M.Thermoluminescence and phototransfer thermoluminescence glow curves, and the corresponding emission spectra of LiF (TLD-100) crystals were studied over the temperature range 100 to 300 K after pre-irradiation heat treatment at 373, 423 and 673 K for 1 h. The TL glow curve displays six glow peaks over this temperature range. The intensity and peak temperatures of glow peaks above 200 K are highly affected by the pre-irradiation heat treatment while the glow peaks below 200 K are not affected by this treatment. The various emission spectra include 'ultraviolet' bands at 5.42, 4.42 and 3.57 eV and 'visible' bands at 3.07, 2.65 and 2.22 eV. The first glow peak, seen at 138 K, emits in both the ultraviolet and visible with similar intensity. The next glow peak, seen at 156 K with reduced intensity, also emits in both regions but with relatively more in the ultraviolet than the visible. The peak intensity and energy of the individual visible emission bands are strongly affected by pre-irradiation heat treatment, while the ultraviolet bands are weakly affected. The data are explained with a band-gap model that extends Mayhugh-Christy's model for thermoluminescence above room temperature.Öğe Thermoluminescence studies of thermally treated CaB4O 7:Dy(Elsevier Ltd, 2010) Tekin E.; Ege A.; Karali T.; Townsend P.D.; Prokic M.Borate based thermoluminescence dosimeters (TLD) show high sensitivity and good TL characteristics. One of the promising material amongst the dosimeters is Dy doped CaB4O7. Spectrally resolved thermoluminescence of Dy doped CaB4O7 shows three glow peaks at about 50 °C, 240 °C and 380 °C, the intensity of the 240 °C glow peak being the maximum. All TL experiments were conducted on a high sensitivity TL spectrometer at Sussex University with a heating rate of 50 °C min -1. Two main emissions associated with the Dy dopant are observed at ~480 and 580 nm. The samples were subjected to a series of treatments including excitation by X-rays and UV laser radiation. As part of the present research CaB4O7:Dy materials were subjected to two different heat treatments; quenching and slow cooling in order to investigate the changes in TL characteristics. © 2010 Elsevier Ltd. All rights reserved.Öğe TL and EPR studies of Cu, Ag and P doped Li2B4O 7 phosphor(2006) Can N.; Karali T.; Townsend P.D.; Yildiz F.Key characteristics of a newly prepared tissue-equivalent, highly sensitive thermoluminescence dosimeter, Li2B4O7:Cu,Ag,P, are presented. The material was developed at the Institute of Nuclear Sciences, Belgrade, in the form of sintered pellets. A new preparation procedure has greatly increased the sensitivity of the basic copper activated lithium borate and the glow curve of Li2B4O7 : Cu,Ag,P consists of a well-defined main dosimetric peak situated at about 460-465 K with a sensitivity which is about four to five times higher than that of LiF : Mg,Ti (TLD-100). The exceptionally good response features of Li2B 4O7 : Cu,Ag,P are attributed to the incorporation of Cu as a dopant. Both low and high temperature emission spectra are presented and the origins of the various emission bands are considered. Additional data are provided from electron paramagnetic resonance measurements. © 2006 IOP Publishing Ltd.
