Investigations of Point Defects in KH₂PO₄ Crystals Using Ab Initio Quantum Methods

Author

Tabitha E. R. Dodson

Date of Award

9-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Nancy C. Giles, PhD

Abstract

Potassium dihydrogen phosphate (KH₂PO₄, or commonly called KDP) crystals can be grown to large sizes and are used for many important devices (fast optical switches, frequency conversion, polarization rotation) for high powered lasers. The nonlinear optical material has a wide intrinsic transparency range. Intrinsic point defects are responsible for several short-lived absorption bands in the visible and ultraviolet regions that affect high-power pulsed laser propagation. The primary intrinsic defects have been experimentally detected in KDP using electron paramagnetic resonance (EPR) experiments. The defect models established thus far include (i) self-trapped holes, (ii) oxygen vacancies, and (iii) hydrogen vacancies. In this research, the quantum chemistry Gaussian software program was successfully used to establish the atomic displacements forming the potential well to "self-trap" the hole in an otherwise perfect region of the crystal. The Gaussian results provide isotropic and anisotropic hyperfine predictions for the self-trapped hole and simulated EPR spectra (using EasySpin) are in excellent agreement with prior experimental work. A cluster approach was used in this work and discussion of cluster size and approach for modeling of defects in KDP will be presented. This research further develops the understanding of the overlap of spin density on neighboring ions in KDP and the resulting nuclear hyperfine values which can be compared to EPR data. The best approach determined by the modeling of self-trapped holes is also applied to the cation and anion vacancy problems. Work was performed on the DOD's High Performance Computer (WPAFB).

AFIT Designator

AFIT-ENP-DS-19-S-021

DTIC Accession Number

AD1084432

Comments

Plain text title: Investigations of Point Defects in KH2PO4 Crystals Using Ab Initio Quantum Methods

Recommended Citation

Dodson, Tabitha E. R., "Investigations of Point Defects in KH₂PO₄ Crystals Using Ab Initio Quantum Methods" (2019). Theses and Dissertations. 2368.
https://scholar.afit.edu/etd/2368