+publisher:"Victoria University of Wellington" +contributor:("Edgar, Andy")

Victoria University of Wellington

1. Sutton, Rebecca Jane. Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes.

Degree: 2013, Victoria University of Wellington

URL: http://hdl.handle.net/10063/2894

► Organic light emitting diodes (OLEDs) are an emerging technology based on electrically conducting polymer films, with great promise for large area lighting and flexible ultra-thin… (more)

▼ Organic light emitting diodes (OLEDs) are an emerging technology based on electrically conducting polymer films, with great promise for large area lighting and flexible ultra-thin displays. However, despite the rapid technological development, there is still a poor understanding of the degradation and spindependent recombination processes that take place inside an OLED. In this thesis, Electron Paramagnetic Resonance (EPR) was used to investigate these processes in blue-emitting OLEDs. A successful procedure was developed and refined for fabricating OLEDs with the structure ITO/PEDOT:PSS/emissive layer/Al/Ag, with and without the PEDOT:PSS hole-transporting layer. The organic emissive layer was either F8BT, PFO, or PVK:OXD-7:FIrpic (PB). These OLEDs were fabricated in air and with a geometry optimised for EPR experiments. Critical features for satisfactory devices were found to be a sufficiently thick organic layer and minimal exposure to the air. A compact apparatus was developed for simultaneous light output, current, and voltage measurements on the OLEDs while in an inert glove box environment. Electroluminescence and current-voltage parameters measured for these devices showed predominantly trap-controlled space-charge-limited conduction. OLEDs with PFO as the emissive layer and with a PEDOT:PSS layer were investigated with conventional, electrically-detected (ED) and optically-detected (OD) EPR techniques. EDEPR and ODEPR signals were observed at ~9.2 GHz and in the low (<50 mT) and high (~330 mT) magnetic field regimes and were found to change markedly with time during operation as the device degraded. The low field signals initially showed a composite broad quenching and superimposed narrow enhancing response centred around zero field strength. These signals were attributed to magneto-resistance (MR) and magneto-electroluminescence (MEL). Following operational ageing, a third, narrow quenching line was observed in the MR and the ratio of the initial two MR responses changed substantially. These effects are tentatively attributed to a hyperfine interaction. For both EDEPR and ODEPR, quenching high field resonances with a g-value (gyromagnetic ratio) of 2.003±0.001 were observed. The current-quenching resonance gradually diminished during operation and after 4–5 hours was replaced by a current-enhancing resonance. The appearance of this latter resonance could be explained by chemical changes in the OLED due to the diffusion of oxygen through the device from the oxygen-plasma-treated ITO. A working model is proposed which can explain this observed change as spindependent trapping and recombination at free radicals, although the model requires further experimentation to test its validity. Advisors/Committee Members: Edgar, Andy, Plank, Natalie.

Subjects/Keywords: Organic electronics; ESR; Magneto-optics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Sutton, R. J. (2013). Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes. (Masters Thesis). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/2894

Chicago Manual of Style (16^th Edition):

Sutton, Rebecca Jane. “Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes.” 2013. Masters Thesis, Victoria University of Wellington. Accessed December 15, 2019. http://hdl.handle.net/10063/2894.

MLA Handbook (7^th Edition):

Sutton, Rebecca Jane. “Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes.” 2013. Web. 15 Dec 2019.

Vancouver:

Sutton RJ. Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes. [Internet] [Masters thesis]. Victoria University of Wellington; 2013. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/10063/2894.

Council of Science Editors:

Sutton RJ. Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes. [Masters Thesis]. Victoria University of Wellington; 2013. Available from: http://hdl.handle.net/10063/2894

Victoria University of Wellington

2. Winch, Nicola Maree. Radiation Imaging with Caesium Bromide Storage Phosphors.

Degree: 2013, Victoria University of Wellington

URL: http://hdl.handle.net/10063/2799

► This thesis is centred on the development of a new method to prepare semitransparent CsBr:Eu²⁺ imaging plates for high resolution X-ray radiography. Methods of characterising… (more)

▼ This thesis is centred on the development of a new method to prepare semitransparent CsBr:Eu²⁺ imaging plates for high resolution X-ray radiography. Methods of characterising the performance of these plates, and their application to dual energy imaging and neutron imaging are discussed. The basic preparation method, based on high-pressure uniaxial compression of powder mixtures of CsBr and EuBr₂, produces imaging plates which show good transparency and resolution. These imaging plates have a conversion efficiency of 1.5 pJmR⁻¹mm⁻³ compared to 5.1 pJmR⁻¹mm⁻³ for a commercial needle imaging plate. Water is found to play a critical role in the photostimulated luminescence activation in CsBr:Eu²⁺ storage phosphors, and imaging plates subsequently hydrated at room temperature have an increased conversion efficiency of up to 11 pJmR⁻¹mm⁻³, better than the commercial material. A model has been suggested for the generation of the PSL active site in the imaging plates based on thermomechanical sintering and water-induced crystal regrowth. A precise method for determining the conversion efficiency and stimulation energy of X-ray storage phosphor materials using an integrating sphere has been developed and used to characterise the materials developed in this thesis. A novel read-out method for storage phosphor imaging plates based on flood illumination and a semi-professional digital camera has also been developed and tested. Good quality X-ray images are obtained and the method shows excellent promise as a low-cost, portable X-ray imaging system. A stratified detector using CsBr imaging plates has been developed for use in dual-energy imaging. Results suggest that it is possible to perform dual-energy imaging with this structure. CsBr:Eu²⁺ imaging plates have been produced with added neutron converters for use as thermal neutron imaging plates. An imaging plate with 5 % ¹ºB₂O₃ added as a neutron converter has a PSL output 50 % that of a commercial neutron imaging plate. Neutron imaging with these imaging plates has been successfully demonstrated. Advisors/Committee Members: Edgar, Andy, Bartle, Murray.

Subjects/Keywords: Storage phosphors; Caesium bromide; Radiation imaging

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Winch, N. M. (2013). Radiation Imaging with Caesium Bromide Storage Phosphors. (Doctoral Dissertation). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/2799

Chicago Manual of Style (16^th Edition):

Winch, Nicola Maree. “Radiation Imaging with Caesium Bromide Storage Phosphors.” 2013. Doctoral Dissertation, Victoria University of Wellington. Accessed December 15, 2019. http://hdl.handle.net/10063/2799.

MLA Handbook (7^th Edition):

Winch, Nicola Maree. “Radiation Imaging with Caesium Bromide Storage Phosphors.” 2013. Web. 15 Dec 2019.

Vancouver:

Winch NM. Radiation Imaging with Caesium Bromide Storage Phosphors. [Internet] [Doctoral dissertation]. Victoria University of Wellington; 2013. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/10063/2799.

Council of Science Editors:

Winch NM. Radiation Imaging with Caesium Bromide Storage Phosphors. [Doctoral Dissertation]. Victoria University of Wellington; 2013. Available from: http://hdl.handle.net/10063/2799

Victoria University of Wellington

3. Gädtke, Christin. Advanced Materials for Radiation Dosimetry.

Degree: 2014, Victoria University of Wellington

URL: http://hdl.handle.net/10063/3298

► The motivation for this work was to find materials that have the following characteristics: good optical transparency, rapid read-out, automation of read-out, good fading characteristic,… (more)

▼ The motivation for this work was to find materials that have the following characteristics: good optical transparency, rapid read-out, automation of read-out, good fading characteristic, promise high sensitivity to ionising radiation, and tissue equivalence for use in medical applications. For example, there are medical applications in brachytherapy and high-energy photon therapy for the treatment of cancer. These applications benefit small dosimeters for monitoring radiation during radiotherapy or for dose verification and validation. This thesis studies fluoroperovskite materials that were manufactured as bulk materials or nanoparticles. The techniques of photoluminescence (PL), radioluminescence (RL), thermoluminescence (TL) and optically stimulated luminescence (OSL) were employed in order to get a deeper understanding of the defect distribution in these materials. A detailed model of the trap distribution was developed from the results of these measurements. It was observed that compared to the bulk materials, the nanoparticles show a lower PL lifetime and less dependence on the dose of the RL intensity, which is due to the different defect distribution. The nanoparticles also demonstrate more low temperature peaks in the TL glow curves. PL and RL measurements of Eu3+ doped samples show that the crystal environment of the Eu3+ in the bulk material is more distorted than for the nanoparticles. For the bulk materials, the thermal coefficient of the RL is <0.4 %/K, which is a desirable property of real -time dosimeters. The thermal coefficient of the RL in the nanoparticles has a high uncertainty ( 7 %/K) compared to the bulk materials ( 0.4 %/K). For the fluoride nanoparticles, it was observed that the PL lifetimes for the LaF3 decreases with increasing rare earth concentrations. This can be attributed to energy transfer from luminescence ions in the core to luminescence ions near the surface followed by non-radiative decay. In comparison, the decrease of the PL lifetimes of RbMgF3 and NaMgF3 is predominantly due to non-radiative recombination centres inside the crystal. Advisors/Committee Members: Williams, Grant, Edgar, Andy.

Subjects/Keywords: Fluoroperovskites; Luminescence; Dosimeter

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Gädtke, C. (2014). Advanced Materials for Radiation Dosimetry. (Doctoral Dissertation). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/3298

Chicago Manual of Style (16^th Edition):

Gädtke, Christin. “Advanced Materials for Radiation Dosimetry.” 2014. Doctoral Dissertation, Victoria University of Wellington. Accessed December 15, 2019. http://hdl.handle.net/10063/3298.

MLA Handbook (7^th Edition):

Gädtke, Christin. “Advanced Materials for Radiation Dosimetry.” 2014. Web. 15 Dec 2019.

Vancouver:

Gädtke C. Advanced Materials for Radiation Dosimetry. [Internet] [Doctoral dissertation]. Victoria University of Wellington; 2014. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/10063/3298.

Council of Science Editors:

Gädtke C. Advanced Materials for Radiation Dosimetry. [Doctoral Dissertation]. Victoria University of Wellington; 2014. Available from: http://hdl.handle.net/10063/3298

Victoria University of Wellington

4. Robinson, Jeremy. A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging.

Degree: 2008, Victoria University of Wellington

URL: http://hdl.handle.net/10063/341

► This thesis presents the results of a photo and thermally stimulated luminescence study of europium-doped barium chloride in relation to its potential application as a… (more)

▼ This thesis presents the results of a photo and thermally stimulated luminescence study of europium-doped barium chloride in relation to its potential application as a storage phosphor in glass ceramics for radiation imaging, particularly for neutron imaging. Previous work done on lithium borate (LiBO) glasses containing BaCl2:Eu2+ nanocrystals at Victoria University of Wellington had demonstrated comparable imaging capability with commercially available BaFBr:Eu2+ based imaging plates, though the sensitivity and spatial resolution were inferior to that material, and there was a substantial afterglow during the read-out process which degraded any image. These problems are addressed here. The effect of various different co-dopants on the storage properties was examined using the thermally stimulated luminescence (TSL) technique, with dopants primarily chosen from the alkali and alkaline earth elements. The resulting glow curves have been analysed to determine the activation energies associated with the various traps, and tentative assignments of structural defects to the various glow curve peaks are proposed. It was found that Li+ and Na+ gave small increases (20% and 50% respectively) in efficiency, though other dopants tended to reduce the overall output. In particular, K+ and Rb+ were found to substantially reduce the output efficiency. It was found that Li+ co-doped BaCl2:Eu2+ contained thermally unstable traps which at room temperature could result in the observed afterglow in LiBO/BaCl2 glass ceramics through a read-out induced phototransfer process. The experimental measurements required substantial hardware and software development of the existing VUW facilities for TSL, and these improvements are also described here. The most significant improvements are an extension of the operating range at the lower end of the existing TSL spectrometer to -50 degrees C through a cooled gas flow system, and the engineering of a completely new system to record TSL from 25 K to 400 K. Advisors/Committee Members: Edgar, Andy.

Subjects/Keywords: BaCl2; Neutron imaging; Imaging plates

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Robinson, J. (2008). A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging. (Masters Thesis). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/341

Chicago Manual of Style (16^th Edition):

Robinson, Jeremy. “A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging.” 2008. Masters Thesis, Victoria University of Wellington. Accessed December 15, 2019. http://hdl.handle.net/10063/341.

MLA Handbook (7^th Edition):

Robinson, Jeremy. “A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging.” 2008. Web. 15 Dec 2019.

Vancouver:

Robinson J. A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging. [Internet] [Masters thesis]. Victoria University of Wellington; 2008. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/10063/341.

Council of Science Editors:

Robinson J. A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging. [Masters Thesis]. Victoria University of Wellington; 2008. Available from: http://hdl.handle.net/10063/341

Victoria University of Wellington

5. Winch, Nicola Maree. Light Scattering in Glass Ceramic X-ray Imaging Plates.

Degree: 2008, Victoria University of Wellington

URL: http://hdl.handle.net/10063/535

► Glass ceramic materials have been suggested as a possible high resolution replacement for current commercial storage phosphor imaging plates. The low spatial frequency of the… (more)

Subjects/Keywords: Storage phosphors; Light scattering; Glass ceramics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Winch, N. M. (2008). Light Scattering in Glass Ceramic X-ray Imaging Plates. (Masters Thesis). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/535

Chicago Manual of Style (16^th Edition):

Winch, Nicola Maree. “Light Scattering in Glass Ceramic X-ray Imaging Plates.” 2008. Masters Thesis, Victoria University of Wellington. Accessed December 15, 2019. http://hdl.handle.net/10063/535.

MLA Handbook (7^th Edition):

Winch, Nicola Maree. “Light Scattering in Glass Ceramic X-ray Imaging Plates.” 2008. Web. 15 Dec 2019.

Vancouver:

Winch NM. Light Scattering in Glass Ceramic X-ray Imaging Plates. [Internet] [Masters thesis]. Victoria University of Wellington; 2008. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/10063/535.

Council of Science Editors:

Winch NM. Light Scattering in Glass Ceramic X-ray Imaging Plates. [Masters Thesis]. Victoria University of Wellington; 2008. Available from: http://hdl.handle.net/10063/535

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