Date of Award

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Committee Member

Joseph W. Kolis

Committee Member

William T. Pennington

Committee Member

Joseph S. Thrasher

Committee Member

Terry M. Tritt

Abstract

In our modern world, lasers are used every day, from the mundane task of playing a DVD to the innovative implementation of laser surgery. Nonlinear optical (NLO) crystals are crucial to laser technology for their ability to modify the frequency of a beam. The development of new NLO crystals is necessary for the advancement of laser technology, in order to reach wavelengths that are not currently accessible due to the limitations of current materials. Of particular importance to semiconductor photolithography, laser micromachining, and scientific instrumentation are the ultra-violet (UV, 200 nm > λ > 400 nm) and deep-UV (λ < 200 nm) portions of the optical spectrum. This dissertation delves into the synthesis of new potential NLO materials by means of hydrothermal crystal growth. In this study, tetrahedral oxides are utilized due to their likelihood of producing noncentrosymmetric (NCS) crystals, a necessity for NLO materials. Silicates are also employed in this study due to their particularly deep absorption edge into the UV. The addition of a spectroscopically silent rare earth ion which is capable of being doped with a lasing ion into a NCS crystal may lead to a single crystal that is both capable of lasing and frequency doubling. In the pursuit of such a crystal, the novel syntheses of Cs3YSi6O15 and LiRESiO4 (RE = Er, Tm, Yb, Lu) were established. Although these materials proved not to be NCS, their structures proved very intriguing and in the case of Cs3YSi6O15 is the parent structure to a family of structures that otherwise exhibits structural disorder or modulation. In expanding the range of mixed oxoanion species, the rare earth ion was replaced with a tetrahedral trivalent oxoanion. The appeal of a series with the general formula ABCO4, (A = alkali ion, B = trivalent metal, and C = tetravalent metal) is its prevalence to produce NCS crystals, notably having a tridymite-type framework. Tridymite is a high temperature variant of quartz that forms six-membered rings propagating through the structure, creating vacant channels. In a stuffed variation of this structural type, rings having negative charge are balanced by the “stuffing” of an alkali or alkaline earth cation into the vacant channels. While the archetype of the stuffed tridymites forms in the centrosymmetric (CS) space group setting of P63/mmc, there are four degrees of freedom that evolve as small variations in the structure are made, often leading to the removal of the inversion center. With the synthesis of a wide array of crystals in this family, those that were found to be NCS were analyzed for their potential use as NLO materials.

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