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Luminescent Materials 2011
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Luminescent Materials 2011

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 March 2011) | Viewed by 66811

Special Issue Editors

Prof. Dr. Magnus Willander

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Guest Editor
Department of Science and Technology (ITN), Campus Norrköping, Linköping University, SE 60174 Norrköping, Sweden
Interests: materials; synthesis; characterization; material application for energy harvesting; devices for sensing; optical and electrical devices
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Dirk Poelman

E-Mail Website
Guest Editor
Lumilab, Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent, Belgium
Interests: lighting, vision, and luminescence, displays; thin film optics; photocatalysis; medical imaging; structural characterization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

While luminescent materials have been known and studied for many decades, new materials, new synthesis methods and novel applications have recently initiated a boost in the research efforts into this class of materials. For example, both organic and inorganic LEDs are rapidly developing as light sources for displays and general lighting, quantum dots are promoted as highly efficient and tunable emitters, storage phosphors are rapidly replacing photographic plates in medical imaging and advanced persistent luminescent materials can be used for emergency and decorative lighting without any external power source than ambient light. In addition, efforts are being made to improve the efficiency of solar cells using fluorescent edge emitting plates, upconversion and quantum cutting phosphors. This special issue aims at presenting a selection of state of the art research topics in the synthesis, analysis, modeling and application of luminescent materials. Both review papers and contributions on original research will be welcomed in the issue.

Prof. Dr. Magnus Willander
Prof. Dr. Dirk Poelman
Guest Editors

Keywords

  • electroluminescence
  • photoluminescence
  • semiconductor materials
  • polymer materials
  • LEDs wavelength conversion
  • persistent luminescence
  • storage phosphors
  • quantum dots
  • exciton emission
  • lighting

Published Papers (5 papers)

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Research

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377 KiB  
Article
Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs)
by Ijaz Hussain, Nargis Bano, Sajjad Hussain, Yousuf Soomro, Omer Nur and Magnus Willander
Materials 2011, 4(7), 1260-1270; https://doi.org/10.3390/ma4071260 - 08 Jul 2011
Cited by 10 | Viewed by 7106
Abstract
In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from [...] Read more.
In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from radiative recombination of the organic and ZnO nanorods (NRs). Depth resolved luminescence was used for probing the nature and spatial distribution of radiative defects, especially to study the re-absorption of ultraviolet (UV) in this hybrid white LEDs structure. At room temperature the cathodoluminescence (CL) spectra intensity of the deep band emission (DBE) is increased with the increase of the electron beam penetration depth due to the increase of defect concentration at the ZnO NRs/Polyfluorene (PFO) interface and probably due to internal absorption of the UV. A strong dependency between the intensity ratio of the UV to the DBE bands and the spatial distribution of the radiative defects in ZnO NRs has been found. The comparison of the CL spectra from the PFO and the ZnO NRs demonstrate that PFO has a very weak violet-blue emission band, which confirms that most of the white emission components originate from the ZnO NRs. Full article
(This article belongs to the Special Issue Luminescent Materials 2011)
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748 KiB  
Article
Defects Identification and Effects of Annealing on Lu2(1-x)Y2xSiO5 (LYSO) Single Crystals for Scintillation Application
by Samuel Blahuta, Aurélie Bessière, Bruno Viana, Vladimir Ouspenski, Eric Mattmann, Julien Lejay and Didier Gourier
Materials 2011, 4(7), 1224-1237; https://doi.org/10.3390/ma4071224 - 01 Jul 2011
Cited by 51 | Viewed by 8359
Abstract
The nature, properties and relative concentrations of electronic defects were investigated by Thermoluminescence (TL) in Lu2(1-x)Y2xSiO5 (LYSO) single crystals. Ce and Tb-doped single crystals, grown by the Czochralski technique (CZ), revealed similar traps in TL. LYSO:Ce single crystals [...] Read more.
The nature, properties and relative concentrations of electronic defects were investigated by Thermoluminescence (TL) in Lu2(1-x)Y2xSiO5 (LYSO) single crystals. Ce and Tb-doped single crystals, grown by the Czochralski technique (CZ), revealed similar traps in TL. LYSO:Ce single crystals were grown by the Floating-Zone technique (FZ) with increasing oxygen concentration in the growth atmosphere. TL intensity is strongly dependent on the oxygen content of the material, and oxygen vacancies are proven to be the main electronic defects in LYSO. The effects of oxidizing and reducing annealing post-treatment on these defects were investigated. While oxidizing treatments efficiently reduce the amount of electronic defects, reducing treatments increase the amount of existing traps. In a thermally assisted tunneling mechanism, the localization of oxygen vacancies around the dopant is discussed. They are shown to be in the close vicinity of the dopant, though not in first neighbor positions. Full article
(This article belongs to the Special Issue Luminescent Materials 2011)
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471 KiB  
Article
Optical Properties of ZnO Nanoparticles Capped with Polymers
by Shingo Tachikawa, Atsushi Noguchi, Takeharu Tsuge, Masahiko Hara, Osamu Odawara and Hiroyuki Wada
Materials 2011, 4(6), 1132-1143; https://doi.org/10.3390/ma4061132 - 17 Jun 2011
Cited by 112 | Viewed by 13207
Abstract
Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the [...] Read more.
Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging Full article
(This article belongs to the Special Issue Luminescent Materials 2011)
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406 KiB  
Article
Luminescent Afterglow Behavior in the M2Si5N8: Eu Family (M = Ca, Sr, Ba)
by Koen Van den Eeckhout, Philippe F. Smet and Dirk Poelman
Materials 2011, 4(6), 980-990; https://doi.org/10.3390/ma4060980 - 27 May 2011
Cited by 81 | Viewed by 9229
Abstract
Persistent luminescent materials are able to emit light for hours after being excited. The majority of persistent phosphors emit in the blue or green region of the visible spectrum. Orange- or red-emitting phosphors, strongly desired for emergency signage and medical imaging, are scarce. [...] Read more.
Persistent luminescent materials are able to emit light for hours after being excited. The majority of persistent phosphors emit in the blue or green region of the visible spectrum. Orange- or red-emitting phosphors, strongly desired for emergency signage and medical imaging, are scarce. We prepared the nitrido-silicates Ca2Si5N8:Eu (orange), Sr2Si5N8:Eu (reddish), Ba2Si5N8:Eu (yellowish orange), and their rare-earth codoped variants (R = Nd, Dy, Sm, Tm) through a solid state reaction, and investigated their luminescence and afterglow properties. In this paper, we describe how the persistent luminescence is affected by the type of codopant and the choice and ratio of the starting products. All the materials exhibit some form of persistent luminescence, but for Sr2Si5N8:Eu,R this is very weak. In Ba2Si5N8:Eu the afterglow remains visible for about 400 s, and Ca2Si5N8:Eu,Tm shows the brightest and longest afterglow, lasting about 2,500 s. For optimal persistent luminescence, the dopant and codopant should be added in their fluoride form, in concentrations below 1 mol%. A Ca3N2 deficiency of about 5% triples the afterglow intensity. Our results show that Ba2Si5N8:Eu(,R) and Ca2Si5N8:Eu(,R) are promising persistent phosphors for applications requiring orange or red light. Full article
(This article belongs to the Special Issue Luminescent Materials 2011)
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Review

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1541 KiB  
Review
Storage Phosphors for Medical Imaging
by Paul Leblans, Dirk Vandenbroucke and Peter Willems
Materials 2011, 4(6), 1034-1086; https://doi.org/10.3390/ma4061034 - 09 Jun 2011
Cited by 160 | Viewed by 27874
Abstract
Computed radiography (CR) uses storage phosphor imaging plates for digital imaging. Absorbed X-ray energy is stored in crystal defects. In read-out the energy is set free as blue photons upon optical stimulation. In the 35 years of CR history, several storage phosphor families [...] Read more.
Computed radiography (CR) uses storage phosphor imaging plates for digital imaging. Absorbed X-ray energy is stored in crystal defects. In read-out the energy is set free as blue photons upon optical stimulation. In the 35 years of CR history, several storage phosphor families were investigated and developed. An explanation is given as to why some materials made it to the commercial stage, while others did not. The photo stimulated luminescence mechanism of the current commercial storage phosphors, BaFBr:Eu2+ and CsBr:Eu2+ is discussed. The relation between storage phosphor plate physical characteristics and image quality is explained. It is demonstrated that the morphology of the phosphor crystals in the CR imaging plate has a very significant impact on its performance. Full article
(This article belongs to the Special Issue Luminescent Materials 2011)
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