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Special Issue "Luminescent Materials"

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

Deadline for manuscript submissions: closed (31 December 2009)

Special Issue Editor

Guest Editor
Prof. Dr. H.T. Hintzen

Energy Materials & Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513 (Helix Building, STW 3.42), 5600 MB Eindhoven, The Netherlands
Phone: +31 40 2473113
Fax: +31 40 2455054
Interests: nitride; energy; luminescence; photocatalysis; phosphor; battery material

Special Issue Information

Dear Colleagues,

Luminescent materials are well known for a long time from traditional lighting and display applications, like cathode-ray (television) tubes, fluorescent lamps but also X-ray screens. Exploration of novel materials classes during the last years has enabled development of new applications, e.g. white LEDs, plasma display panels, bio-markers and solar cells. Recent progress and future prospects show that luminescent materials remain not only interesting from a scientific point of view but also relevant from an application point of view. For many years to come, scientific challenges as well as societal needs in this research field can be addressed by chemists, physicists and materials scientists. This special issue reviews the latest developments on these novel luminescent materials, their preparation, crystal chemistry, characterization and optical properties. The intention is to focus on the relationship between the luminescence properties on the one hand and the chemical composition and structure on the other. Contributions as review or original papers on basic research or applied technology of promising luminescent materials are welcomed.

Prof. Dr. H.T. Hintzen
Guest Editor

Keywords

  • luminescence
  • down-conversion
  • up-conversion
  • quantum-cutting
  • luminescent material
  • phosphor
  • quantum dot
  • LED
  • solar cell
  • display
  • bio-marker

Published Papers (19 papers)

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Research

Jump to: Review

Open AccessArticle Role of Fluxes in Optimizing the Optical Properties of Sr0.95Si2O2N2:0.05Eu2+ Green-Emitting Phosphor
Materials 2013, 6(7), 2862-2872; doi:10.3390/ma6072862
Received: 10 April 2013 / Revised: 14 June 2013 / Accepted: 8 July 2013 / Published: 15 July 2013
Cited by 5 | PDF Full-text (1194 KB) | HTML Full-text | XML Full-text
Abstract
Chlorides of NH4Cl and SrCl2 and fluorides of AlF3 and SrF2 were added to raw materials acting as the flux for preparing the SrSi2O2N2:Eu2+ phosphor. The effects of the fluxes [...] Read more.
Chlorides of NH4Cl and SrCl2 and fluorides of AlF3 and SrF2 were added to raw materials acting as the flux for preparing the SrSi2O2N2:Eu2+ phosphor. The effects of the fluxes on the phase formation, particle morphology, particle size, and photoluminescence properties were investigated. The results revealed that particle size, particle morphology and photoluminescence intensity were largely dominated by the type of the flux material and its adding amount. The chloride-based flux was found to favor the formation of the SrSi2O2N2:Eu2+ phase. Among the chloride-based fluxes, the sample added with the SrCl2 flux presented the narrow particle distribution and cleaner surface, with enhanced emission intensity and an increased external quantum efficiency by 68% and 22%, respectively, compared with those of the sample without any flux adding. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessArticle Experimental Determination of the Fluorescence Quantum Yield of Semiconductor Nanocrystals
Materials 2011, 4(7), 1182-1193; doi:10.3390/ma4071182
Received: 30 April 2011 / Revised: 23 June 2011 / Accepted: 27 June 2011 / Published: 30 June 2011
Cited by 7 | PDF Full-text (242 KB) | HTML Full-text | XML Full-text
Abstract
Many studies have considered the luminescence of colloidal II–VI nanocrystals, both in solution at a collective scale and at an individual scale by confocal microscopy. The quantum yield is an important figure of merit for the optical quality of a fluorophore. We [...] Read more.
Many studies have considered the luminescence of colloidal II–VI nanocrystals, both in solution at a collective scale and at an individual scale by confocal microscopy. The quantum yield is an important figure of merit for the optical quality of a fluorophore. We detail here a simple method to determine the quantum yield of nanocrystals in solution as a function of the absorption. For this purpose, we choose rhodamine 101 as a reference dye to measure the nanocrystal fluorescence quantum yield. The influence of the concentration on quantum yield is therefore studied for both the reference and the solutions of nanocrystals and is found to be critical for the acuity of the method. Different types of nanocrystals are studied to illustrate different quantum yield evolutions with the concentration. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessArticle Synthesis of Green-Emitting (La,Gd)OBr:Tb3+ Phosphors
Materials 2010, 3(4), 2506-2515; doi:10.3390/ma3042506
Received: 29 December 2009 / Revised: 12 March 2010 / Accepted: 31 March 2010 / Published: 1 April 2010
Cited by 11 | PDF Full-text (347 KB) | HTML Full-text | XML Full-text
Abstract
Green-emitting phosphors based on lanthanum-gadolinium oxybromide were synthesized in a single phase form by the conventional solid state reaction method, and photoluminescence properties of them were characterized. The excitation peak wavelength of (La1-xGdx)OBr:Tb3+ shifted to the [...] Read more.
Green-emitting phosphors based on lanthanum-gadolinium oxybromide were synthesized in a single phase form by the conventional solid state reaction method, and photoluminescence properties of them were characterized. The excitation peak wavelength of (La1-xGdx)OBr:Tb3+ shifted to the shorter wavelength side with the increase in the crystal field around the Tb3+ ions by doping Gd3+ ions into the La3+ site, and, as a result, the green emission intensity was successfully enhanced. The maximum emission intensity was obtained for (La0.95Gd0.05)OBr:5%Tb3+, where the relative emission intensity was 45% of that of a commercial green-emitting LaPO4:Ce3+,Tb3+ phosphor. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessArticle Layer-Inversion Zones in Angular Distributions of Luminescence and Absorption Properties in Biaxial Crystals
Materials 2010, 3(4), 2474-2482; doi:10.3390/ma3042474
Received: 13 January 2010 / Accepted: 29 March 2010 / Published: 31 March 2010
Cited by 3 | PDF Full-text (421 KB) | HTML Full-text | XML Full-text
Abstract
We numerically depict the complete angular distributions of luminescence and absorption properties in biaxial media, by calculating the imaginary part of the optical index for all directions of propagation. Our simulations show a double-layer surface with specific topology and symmetry properties that [...] Read more.
We numerically depict the complete angular distributions of luminescence and absorption properties in biaxial media, by calculating the imaginary part of the optical index for all directions of propagation. Our simulations show a double-layer surface with specific topology and symmetry properties that greatly differ from those of the refractive index surface. Our calculations show that the two layers intersect and inverse themselves along continuous loci related to polarization-independent luminescence or absorption properties. Specificities related to the orthorhombic, monoclinic and triclinic biaxial crystal systems are discussed. Such theoretical developments should be considered to fully exploit innovating luminescent materials. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessArticle Spectroscopy and 1μm Luminescence by Visible Quantum Cutting in Pr3+-Yb3+ Codoped Glass
Materials 2010, 3(4), 2405-2411; doi:10.3390/ma3042405
Received: 28 December 2009 / Revised: 25 January 2010 / Accepted: 25 March 2010 / Published: 29 March 2010
Cited by 10 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
The quantum cutting phenomenon of a blue photon into two infrared photons is reported in glass codoped with Pr3+-Yb3+ ions. Oxyfluoride glass with compositions of 32SrF2-0.1PrF3-2.9YbF3-42SiO2-23Al2O3 were prepared, [...] Read more.
The quantum cutting phenomenon of a blue photon into two infrared photons is reported in glass codoped with Pr3+-Yb3+ ions. Oxyfluoride glass with compositions of 32SrF2-0.1PrF3-2.9YbF3-42SiO2-23Al2O3 were prepared, and photoluminescence properties in the range from visible to near-infrared were investigated. Evidence of several energy transfers, such as (Pr3+:3P01G4)→(Yb3+:2F5/22F7/2) and (Pr3+:1D23F4, 3F3)→(Yb3+:2F5/22F7/2), were demonstrated in the Pr3+-Yb3+ co-doped glass. By comparing excitation spectrum of the Yb3+ emission with absorption spectrum of Pr3+, we obtain direct evidence of quantum cutting by excitation to Pr3+:3PJ levels at 420 ~ 490 nm. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessArticle Crystal and Electronic Structures, Photoluminescence Properties of Eu2+-Doped Novel Oxynitride Ba4Si6O16-3x/2Nx
Materials 2010, 3(3), 1692-1708; doi:10.3390/ma3031692
Received: 7 January 2010 / Revised: 12 February 2010 / Accepted: 5 March 2010 / Published: 8 March 2010
Cited by 13 | PDF Full-text (992 KB) | HTML Full-text | XML Full-text
Abstract
The crystal structure and the photoluminescence properties of novel green Ba4-yEuySi6O16-3x/2Nx phosphors were investigated. The electronic structures of the Ba4Si6O16 host were calculated by first principles pseudopotential method [...] Read more.
The crystal structure and the photoluminescence properties of novel green Ba4-yEuySi6O16-3x/2Nx phosphors were investigated. The electronic structures of the Ba4Si6O16 host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Γ. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba4-yEuySi6O16-3x/2Nx solid solutions crystallized in a monoclinic (space group P21/c, Z = 2) having the lattice parameters a = 12.4663(5) Å, b = 4.6829(2) Å, c = 13.9236(6) Å, and β = 93.61(1)°, with a maximum solubility of nitrogen at about x = 0.1. Ba4Si6O16-3x/2Nx:Eu2+ exhibits efficient green emission centered at 515–525 nm varying with the Eu2+ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (λexc = 375 nm), the absorption and quantum efficiency of Ba4-yEuySi6O16-3x/2Nx (x = 0.1, y = 0.2) reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba4-yEuySi6O16-3x/2Nx is promising for application in white UV-LEDs. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessArticle Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs
Materials 2010, 3(3), 1497-1508; doi:10.3390/ma3031497
Received: 1 January 2010 / Revised: 24 February 2010 / Accepted: 24 February 2010 / Published: 26 February 2010
Cited by 8 | PDF Full-text (447 KB) | HTML Full-text | XML Full-text
Abstract
An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW) on GaAs by molecular beam epitaxy (MBE) are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 [...] Read more.
An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW) on GaAs by molecular beam epitaxy (MBE) are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM) of ~60 meV in room temperature (RT) photoluminescence (PL) indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Review

Jump to: Research

Open AccessReview Emission Properties, Solubility, Thermodynamic Analysis and NMR Studies of Rare-Earth Complexes with Two Different Phosphine Oxides
Materials 2010, 3(8), 4080-4108; doi:10.3390/ma3084080
Received: 14 June 2010 / Accepted: 16 July 2010 / Published: 26 July 2010
Cited by 5 | PDF Full-text (898 KB) | HTML Full-text | XML Full-text
Abstract
The paper proposes novel molecular designs for rare-earth complexes involving the introduction of two different phosphine oxide structures into one rare-earth ion. These designs are effective for improving solubility and emission intensity. Additionally, the complexes are indispensable for realizing high performances in [...] Read more.
The paper proposes novel molecular designs for rare-earth complexes involving the introduction of two different phosphine oxide structures into one rare-earth ion. These designs are effective for improving solubility and emission intensity. Additionally, the complexes are indispensable for realizing high performances in LEDs and security media. The thermodynamic properties of Eu(III) complexes are correlated with the solubility. Correlations between coordination structures and emission intensity were explained by NMR analysis. The luminous flux of red LED devices with Eu(III) complexes is very high (20 mA, 870 m lumen). A new white LED has its largest spectra intensity in the red region and a human look much more vividly under this light. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessReview Rare-Earth Activated Nitride Phosphors: Synthesis, Luminescence and Applications
Materials 2010, 3(6), 3777-3793; doi:10.3390/ma3063777
Received: 17 May 2010 / Accepted: 17 June 2010 / Published: 21 June 2010
Cited by 96 | PDF Full-text (323 KB) | HTML Full-text | XML Full-text
Abstract
Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, [...] Read more.
Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Preparations and Characterizations of Luminescent Two Dimensional Organic-inorganic Perovskite Semiconductors
Materials 2010, 3(5), 3385-3406; doi:10.3390/ma3053385
Received: 20 March 2010 / Revised: 7 May 2010 / Accepted: 18 May 2010 / Published: 25 May 2010
Cited by 24 | PDF Full-text (1000 KB)
Abstract
This article reviews the synthesis, structural and optical characterizations of some novel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors. These 2DOIP semiconductors show a self-assembled nano-layered structure, having the electronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles have been prepared [...] Read more.
This article reviews the synthesis, structural and optical characterizations of some novel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors. These 2DOIP semiconductors show a self-assembled nano-layered structure, having the electronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles have been prepared through different methods. The structures of the 2DOIP semiconductors are characterized by atomic force microscopy and X-ray diffraction. The optical properties of theb DOIP semiconductors are characterized from absorption and photoluminescence spectra measured at room and low temperatures. Influences of different components, in particular the organic parts, on the structural and optical properties of the 2DOIP semiconductors are discussed. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Luminescence in Sulfides: A Rich History and a Bright Future
Materials 2010, 3(4), 2834-2883; doi:10.3390/ma3042834
Received: 8 April 2010 / Accepted: 18 April 2010 / Published: 21 April 2010
Cited by 93 | PDF Full-text (1294 KB) | HTML Full-text | XML Full-text
Abstract
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the [...] Read more.
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Luminescence from Zinc Oxide Nanostructures and Polymers and their Hybrid Devices
Materials 2010, 3(4), 2643-2667; doi:10.3390/ma3042643
Received: 4 January 2010 / Revised: 15 March 2010 / Accepted: 31 March 2010 / Published: 12 April 2010
Cited by 122 | PDF Full-text (1626 KB) | HTML Full-text | XML Full-text
Abstract
Zinc oxide (ZnO) is a strong luminescent material, as are several polymers. These two materials have distinct drawbacks and advantages, and they can be combined to form nanostructures with many important applications, e.g., large-area white lighting. This paper discusses the origin of [...] Read more.
Zinc oxide (ZnO) is a strong luminescent material, as are several polymers. These two materials have distinct drawbacks and advantages, and they can be combined to form nanostructures with many important applications, e.g., large-area white lighting. This paper discusses the origin of visible emission centers in ZnO nanorods grown with different approaches. White light emitting diodes (LEDs) were fabricated by combining n-ZnO nanorods and hollow nanotubes with different p-type materials to form heterojunctions. The p-type component of the hybrids includes p-SiC, p-GaN, and polymers. We conclude by analyzing the electroluminescence of the different light emitting diodes we fabricated. The observed optical, electrical, and electro-optical characteristics of these LEDs are discussed with an emphasis on the deep level centers that cause the emission. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Persistent Luminescence in Eu2+-Doped Compounds: A Review
Materials 2010, 3(4), 2536-2566; doi:10.3390/ma3042536
Received: 17 January 2001 / Revised: 27 March 2010 / Accepted: 30 March 2010 / Published: 6 April 2010
Cited by 257 | PDF Full-text (463 KB) | HTML Full-text | XML Full-text
Abstract
In 1996, Matsuzawa et al. reported on the extremely long-lasting afterglow of SrAl2O4:Eu2+ codoped with Dy3+ ions, which was more than 10-times brighter than the previously widely used ZnS:Cu,Co. Since then, research for stable and [...] Read more.
In 1996, Matsuzawa et al. reported on the extremely long-lasting afterglow of SrAl2O4:Eu2+ codoped with Dy3+ ions, which was more than 10-times brighter than the previously widely used ZnS:Cu,Co. Since then, research for stable and efficient persistent phosphors has continuously gained popularity. However, even today - almost 15 years after the discovery of SrAl2O4:Eu2+, Dy3+ - the number of persistent luminescent materials is still relatively low. Furthermore, the mechanism behind this phenomenon is still unclear. Although most authors agree on the general features, such as the existence of long-lived trap levels, many details are still shrouded in mystery. In this review, we present an overview of the important classes of known persistent luminescent materials based on Eu2+-emission and how they were prepared, and we take a closer look at the models and mechanisms that have been suggested to explain bright afterglow in various compounds. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Fabrication Methods and Luminescent Properties of ZnO Materials for Light-Emitting Diodes
Materials 2010, 3(4), 2218-2259; doi:10.3390/ma3042218
Received: 15 January 2010 / Revised: 8 February 2010 / Accepted: 19 March 2010 / Published: 24 March 2010
Cited by 35 | PDF Full-text (1443 KB) | HTML Full-text | XML Full-text
Abstract
Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high [...] Read more.
Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high optical gain of 320 cm−1 at room temperature. Its luminescent properties have been intensively investigated for samples, in the form of bulk, thin film, or nanostructure, prepared by various methods and doped with different impurities. In this paper, we first review briefly the recent progress in this field. Then a comprehensive summary of the research carried out in our laboratory on ZnO preparation and its luminescent properties, will be presented, in which the involved samples include ZnO films and nanorods prepared with different methods and doped with n-type or p-type impurities. The results of ZnO based LEDs will also be discussed. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Quantum Dots and Their Multimodal Applications: A Review
Materials 2010, 3(4), 2260-2345; doi:10.3390/ma3042260
Received: 5 January 2010 / Revised: 7 March 2010 / Accepted: 23 March 2010 / Published: 24 March 2010
Cited by 166 | PDF Full-text (2617 KB) | HTML Full-text | XML Full-text
Abstract
Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound [...] Read more.
Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessReview Light Converting Inorganic Phosphors for White Light-Emitting Diodes
Materials 2010, 3(3), 2172-2195; doi:10.3390/ma3032172
Received: 6 January 2010 / Revised: 23 February 2010 / Accepted: 15 March 2010 / Published: 22 March 2010
Cited by 176 | PDF Full-text (1095 KB) | HTML Full-text | XML Full-text
Abstract
White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue [...] Read more.
White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or near-ultraviolet (nUV) LEDs) and photoluminescence phosphors. These solid-state LED lamps, rather than organic light emitting diode (OLED) or polymer light-emitting diode (PLED), have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability and long operating lifetime. To meet with the further requirement of high color rendering index, warm light with low color temperature, high thermal stability and higher energy efficiency for WLEDs, new phosphors that can absorb excitation energy from blue or nUV LEDs and generate visible emissions efficiently are desired. The criteria of choosing the best phosphors, for blue (450-480 nm) and nUV (380-400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance of light between the emission from blue-nUV LEDs and the emissions from phosphors (such as yellow from Y3Al5O12:Ce3+) is important to obtain white light with proper color rendering index and color temperature. Here, we will review the status of phosphors for LEDs and prospect the future development. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Preparation and Characterization of Rare Earth Doped Fluoride Nanoparticles
Materials 2010, 3(3), 2053-2068; doi:10.3390/ma3032053
Received: 26 December 2009 / Revised: 14 January 2010 / Accepted: 18 March 2010 / Published: 19 March 2010
Cited by 25 | PDF Full-text (1344 KB) | HTML Full-text | XML Full-text
Abstract
This paper reviews the synthesis, structure and applications of metal fluoride nanoparticles, with particular focus on rare earth (RE) doped fluoride nanoparticles obtained by our research group. Nanoparticles were produced by precipitation methods using the ligand ammonium di-n-octadecyldithiophosphate (ADDP) that [...] Read more.
This paper reviews the synthesis, structure and applications of metal fluoride nanoparticles, with particular focus on rare earth (RE) doped fluoride nanoparticles obtained by our research group. Nanoparticles were produced by precipitation methods using the ligand ammonium di-n-octadecyldithiophosphate (ADDP) that allows the growth of shells around a core particle while simultaneously avoiding particle aggregation. Nanoparticles were characterized on their structure, morphology, and luminescent properties. We discuss the synthesis, properties, and application of heavy metal fluorides; specifically LaF3:RE and PbF2, and group IIA fluorides. Particular attention is given to the synthesis of core/shell nanoparticles, including selectively RE-doped LaF3/LaF3, and CaF2/CaF2 core/(multi-)shell nanoparticles, and the CaF2-LaF3 system. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Materials for Powder-Based AC-Electroluminescence
Materials 2010, 3(2), 1353-1374; doi:10.3390/ma3021353
Received: 31 December 2009 / Revised: 11 February 2010 / Accepted: 20 February 2010 / Published: 23 February 2010
Cited by 20 | PDF Full-text (12376 KB) | HTML Full-text | XML Full-text
Abstract
At present, thick film (powder based) alternating current electroluminescence (AC-EL) is the only technology available for the fabrication of large area, laterally structured and coloured light sources by simple printing techniques. Substrates for printing may be based on flexible polymers or glass, [...] Read more.
At present, thick film (powder based) alternating current electroluminescence (AC-EL) is the only technology available for the fabrication of large area, laterally structured and coloured light sources by simple printing techniques. Substrates for printing may be based on flexible polymers or glass, so the final devices can take up a huge variety of shapes. After an introduction of the underlying physics and chemistry, the review highlights the technical progress behind this development, concentrating on luminescent and dielectric materials used. Limitations of the available materials as well as room for further improvement are also discussed. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Progress to a Gallium-Arsenide Deep-Center Laser
Materials 2009, 2(4), 1599-1635; doi:10.3390/ma2041599
Received: 14 September 2009 / Revised: 9 October 2009 / Accepted: 20 October 2009 / Published: 22 October 2009
Cited by 5 | PDF Full-text (3781 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
Although photoluminescence from gallium-arsenide (GaAs) deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon [...] Read more.
Although photoluminescence from gallium-arsenide (GaAs) deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon effect, hotoluminescence. Second, we describe our recent work: insensitivity of photoluminescence with heating, striking differences between electroluminescence and photoluminescence, correlation between transitions to deep-states and absence of bandgap-emission. Room-temperature stimulated-emission from GaAs deep-centers was observed at low electrical injection, and could be tuned from the bandgap to half-the-bandgap (900–1,600 nm) by changing the electrical injection. The first GaAs deep-center laser was demonstrated with electrical injection, and exhibited a threshold of less than 27 mA/cm2 in continuous-wave mode at room temperature at the important 1.54 μm fiber-optic wavelength. This small injection for laser action was explained by fast depopulation of the lower state of the optical transition (fast capture of free holes onto deep-centers), which maintains the population inversion. The evidence for laser action included: superlinear L-I curve, quasi-Fermi level separations satisfying Bernard-Duraffourg’s criterion, optical gains larger than known significant losses, clamping of the optical-emission from lossy modes unable to reach laser action, pinning of the population distribution during laser action. Full article
(This article belongs to the Special Issue Luminescent Materials)
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