Soft X-ray Spectroscopy of Metal Nitrides and Oxides: Uncovering Structure-property Relationships in Phosphors for pc-LEDs
Date
2017-06-14
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
This thesis engages a problem that is seemingly a little incongruous: to develop an under-
standing of, and link together, the structure-property relationships of LED-phosphors and
frontier polymorphs of vanadium oxides using the same experimental and theoretical frame-
work. Soft x-ray spectroscopy and density functional theory calculations are used as the
probe of, and interpretive tool for, the electronic structures of these materials. By comparing
and contrasting the observed electronic structures to those of other, similar systems, changes
in electronic structure are linked to changes in crystal structure and atomic composition.
From this vantage point the LED-phosphors, which are essentially metal nitrides, and vana-
dium oxides are not as disparate as they would seem at first glance. Their properties lie on a
continuum, allowing them to be readily understood within a single framework. At the same
time, there are significant insights to be gained about each group, by studying the other.
In both groups the interplay between localization and delocalization of metal d-states
is seen to be key to their functional properties, both as a result of and in conjunction with,
the influence of their ligands. The effects of the ligands are seen to stem directly from their
local charge densities, as well as their separation from and arrangement around the metal
sites. In addition the interaction of non-metal sites is seen to be critical in many cases.
Structure-property relationships are outlined for this suite of materials. Critical material
properties, such as the band gaps, and the location of metal states in the band gaps, are
determined experimentally. Several analysis techniques are developed that prove critical
for the analyses of these compounds. Included in this is a thorough analysis of x-ray self-
absorption in vanadium oxides, which is too often ignored. Ultimately a coherent framework
for understanding the properties of these compounds is developed and it is hoped that this
will serve as the basis of further refinement of their useful properties.
Description
Keywords
Materials Science
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Physics and Engineering Physics
Program
Physics