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Phosphors for Laser Lighting Applica...

Cozzan, Clayton Joseph.

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Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites./
Author:	Cozzan, Clayton Joseph.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	226 p.
Notes:	Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.
Contained By:	Dissertation Abstracts International80-03B(E).
Subject:	Materials science. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10839290
ISBN:	9780438627918

Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites.
Cozzan, Clayton Joseph.

Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 226 p.

Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.

Thesis (Ph.D.)--University of California, Santa Barbara, 2018.

Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state sources, and understanding the intricacies of phosphor structure is key to set the stage for improved, more efficient functionality. The following dissertation begins with an introduction to the fundamentals of solid state lighting, phosphors, and a summary of some recent advances in the field. This is followed by a study to understand structural ordering in the framework of the commercial green-emitting phosphor material, beta-Si 6-zAlzOzN 8-z, as a function of Al content. SiAlON ceramics, solid solutions based on the Si3N4 structure, are important, lightweight structural materials with intrinsically high strength, high hardness, and high thermal and chemical stability. Described by the chemical formula beta-Si 6-zAlzOzN 8-z, from a compositional viewpoint, these materials can be regarded as solid solutions between Si3N4 and Al 3O3N. A key aspect of the structural evolution with increasing Al and O (z in the formula) is to understand how these elements are distributed on the beta-Si3N4 framework. The average and local structure evolution of highly phase-pure samples of beta-Si 6-zAlzOzN 8-z with z = 0.050, 0.075, and 0.125 are studied using a combination of X-ray diffraction, nuclear magnetic resonance studies, and density functional theory calculations. Synchrotron X-ray diffraction establish sample purity and indicate subtle changes in average structure with increasing Al content in these compounds. 27Al solid-state magic angle spinning nuclear magnetic resonance (NMR) experiments, coupled with detailed ab initio calculations of NMR spectra of Al in different AlOqN4--q tetrahedra (0 ≤ q ≤ 4), reveal a tendency of Al and O to cluster in these materials, more specifically, a high propensity for AlON3 tetrahedral motifs to be distributed on the SiAlON framework. Independently, the calculations suggest an energetic preference for Al--O bond formation, instead of a random distribution, in the beta-SiAlON system.

ISBN: 9780438627918Subjects--Topical Terms:

543314
Materials science.

Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites.
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245 1 0 $a Phosphors for Laser Lighting Applications: Structural Evolution, Dense Monoliths, and Thermally Stable Composites.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2018
300 $a 226 p.
500 $a Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.
500 $a Adviser: Ram Seshadri.
502 $a Thesis (Ph.D.)--University of California, Santa Barbara, 2018.
520 $a Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state sources, and understanding the intricacies of phosphor structure is key to set the stage for improved, more efficient functionality. The following dissertation begins with an introduction to the fundamentals of solid state lighting, phosphors, and a summary of some recent advances in the field. This is followed by a study to understand structural ordering in the framework of the commercial green-emitting phosphor material, beta-Si 6-zAlzOzN 8-z, as a function of Al content. SiAlON ceramics, solid solutions based on the Si3N4 structure, are important, lightweight structural materials with intrinsically high strength, high hardness, and high thermal and chemical stability. Described by the chemical formula beta-Si 6-zAlzOzN 8-z, from a compositional viewpoint, these materials can be regarded as solid solutions between Si3N4 and Al 3O3N. A key aspect of the structural evolution with increasing Al and O (z in the formula) is to understand how these elements are distributed on the beta-Si3N4 framework. The average and local structure evolution of highly phase-pure samples of beta-Si 6-zAlzOzN 8-z with z = 0.050, 0.075, and 0.125 are studied using a combination of X-ray diffraction, nuclear magnetic resonance studies, and density functional theory calculations. Synchrotron X-ray diffraction establish sample purity and indicate subtle changes in average structure with increasing Al content in these compounds. 27Al solid-state magic angle spinning nuclear magnetic resonance (NMR) experiments, coupled with detailed ab initio calculations of NMR spectra of Al in different AlOqN4--q tetrahedra (0 ≤ q ≤ 4), reveal a tendency of Al and O to cluster in these materials, more specifically, a high propensity for AlON3 tetrahedral motifs to be distributed on the SiAlON framework. Independently, the calculations suggest an energetic preference for Al--O bond formation, instead of a random distribution, in the beta-SiAlON system.
520 $a Next, an average structure and coordination environment analysis of the robust and efficient green-emitting phosphor, beta-SiAlON:Eu2+ (beta-Si6--zAlzO zN8-zEu0.009), is combined with a range of property measurements to elucidate the role of Al content (z) on luminescence properties, including the red shift of emission and the thermal quenching of luminescence as a function of increasing Al content z. Average structure techniques reveal changes in polyhedral distortion with increasing z for the 9-coordinate Eu site in beta-SiAlON:Eu 2+. X-ray absorption near edge structure (XANES) is used to confirm that the majority of the activator Eu is in the Eu2+ state, exhibiting the symmetry-allowed and efficient 4f7 5d0→4f 65d1 transitions. Room temperature and temperature-dependent luminescence indicate an curious increase in thermal stability with increasing z over a small range due to an increasing barrier for thermal ionization, which is correlated to an increase in the quantum yield of the phosphor. The works shows that specific emission properties can be targeted via compositional tuning, such as narrower emission beta-SiAlON:Eu 2+ (low z) for lower temperature operation, or maximum quantum yield and improved thermal stability (higher z up to 0.125) for high flux and/or high temperature operation.
520 $a With some fundamentals of phosphor structure-property relationships elucidated, we can now take steps to engineer these materials into useful morphologies. High power light emitting diodes (LEDs) and laser diodes (LDs) are being explored for white light generation and visible light communication, and thermally stable encapsulation schemes for color-converting inorganic phosphors are essential to their success. In the first example of thermally robust phosphors for laser-based lighting in the current thesis, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17 (BAM:Eu 2+), has been prepared using microwave-assisted heating (25 min) and densified into a ceramic phosphor using spark plasma sintering (30 min), resulting in translucent samples that emit blue light when incident with a UV laser diode. Results of the refinement on synchrotron X-ray diffraction data demonstrate the viability of microwave assisted heating for faster preparation of phase pure BaMgAl10O17:Eu2+ . The emission properties of the initial powder and the translucent sample have been studied using both a xenon lamp and a violet LD, and reveal the quantum yield of the starting powder does not change from densification into a translucent sample, and could likely be improved using optimized starting powders. Results indicate promise for uses of this blue phosphor in laser-based applications, as well as demonstrating a viable and fast way to prepare dense monolithic phosphors for laser light conversion. (Abstract shortened by ProQuest.).
590 $a School code: 0035.
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650 4 $a Inorganic chemistry. $3 3173556
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