Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Eric M. Golden, PhD.

Abstract

Silver-doped lithium tetraborate (Li2B4O7) crystals emit optically stimulated luminescence (OSL) in response to stimulating light around 400 nm. Photoluminescence, optical absorption, and electron paramagnetic resonance (EPR) were used to identify the defects in the crystal that cause this OSL. Lithium tetraborate crystals have Ag+ ions at Li+ sites and at interstitial sites. Upon ionization at room temperature via x rays, electron-hole pairs are generated. The electrons are trapped at Ag+ occupying interstitial sites, while the holes are trapped at Ag+ at lithium sites. The trapped electron centers become Ag0 (4d105s1) and the trapped hole centers, or recombination centers, become Ag2+ (4d9). Evidence for these centers is seen in EPR at room temperature. Optical absorption of the irradiated crystal showed a broad peak near 370 nm. Bleaching with 400 nm light decreased the EPR signals of the Ag0 and Ag2+ centers. When the crystal was stimulated with 400 nm light, OSL was produced with 270 nm emission. The effects of the stimulating light’s flux on OSL were observed by using xenon lamp and diode laser sources. OSL, with the laser at 405 nm, decayed faster, and provided insight on the existence of a competing electron trap, oxygen vacancies.

AFIT Designator

AFIT-ENP-MS-16-M-075

DTIC Accession Number

AD1053909

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