Structure-Composition Relationships and Their Influence on Long Luminescent Lifetimes in Persistent Luminescent Phosphors

Persistent luminescence (PersL) is an optical phenomenon found in inorganic materials, where a luminescent center, e.g., Eu2+ or Cr3+, is substituted into a host inorganic crystal structure, producing visible light on the order of minutes to hours. The mechanism driving PersL is generally agreed to arise from a relationship between the host structure’s bandgap and any lattice defects stemming from anion vacancies, anti-site defects, and co-dopants, e.g., Dy3+, that form electron traps. Research has primarily focused on establishing methods to improve the long luminescent lifetimes of known persistent luminescent phosphors (PLPs) and the extension of these materials into medical diagnostic applications. However, the PLPs available today have a limited range of emission wavelengths, low efficiency, and lack chemically stability. Developing novel PLPs requires a fundamental understanding of the relationship between the crystal structures and chemical compositions that bring about these distinctive optical properties. Until recently, it was thought that the 5d-orbitals present from a co-dopant were mainly responsible for creating electron traps; yet, thermoluminescence experiments proved a co-dopant was not necessary to observe PersL. This supports the notion that lattice defects are the main electron traps driving PersL. The work presented herein addresses this question using a combination of experimental and computational chemistry tools to identify the intrinsic nature of the electron traps and their relationship to the optical properties. Detailed structural studies were first employed using high resolution synchrotron X-ray diffraction to show compositional control in a solid solution, while X-ray absorption spectroscopy revealed distortions around the luminescent center are linked to anti-site defects. Next, thermoluminescence spectroscopy and computational modeling provided the link between chemical composition and presence of lattice defects to the efficiency of PersL. Finally, a novel synthesis approach to particle size reduction demonstrated an improvement to PersL by inducing surface defects while maintaining chemical composition. The results highlight the importance of investigating the connection between lattice defects, structural properties, e.g., local polyhedral distortion, and optical properties such as PersL. Together, a stronger fundamental understanding of crystal structures and compositions of PLPs will advance the discovery of novel materials.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Houston

Year dc:date.issued

2019

Author dc:creator

• Finley, Erin 1978-

Advisor dc:contributor.advisor

• Brgoch, Jakoah

Committee members dc:contributor.committeemember

• Halasyamani, P. Shiv
• Teets, Thomas S.
• Xu, Shoujun
• Bao, Jiming

• Lattice defects
• Solid solutions

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10657/5806

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/5806