NSF Award
1611198
Non-Technical Abstract<br/>Nonlinear optical (NLO) crystals are used to shift the coherent, monochromatic light of lasers to other desirable wavelengths. Infrared nonlinear optical applications include, stand-off detection of drugs and explosives, non-invasive medical diagnosis and monitoring by breath analysis using molecular spectroscopy and infrared counter-measure systems used to defend military aircraft, just to name a few. However, the current commercially available crystals for use in infrared nonlinear optical devices suffer from drawbacks and are lacking in critical areas that limit their practical applications. The discovery of new infrared nonlinear optical materials enables the realization of new applications impacting medical, industrial and military sectors. Furthermore, the synthesis of improved infrared nonlinear optical materials allows for more reliable, longer-lasting devices having greater impact in areas where these materials have already found utility. Better understanding the relationship between the structure of the crystal and its resulting properties allows for faster progress in this field. Through this project, structure-property correlations are evolving from systematic studies of quaternary diamond-like semiconductors that combine strategic experimentation with theory, in which the ability to reliably predict properties is fostered by experimental results. These structure-property relationships are being revealed by the research efforts of postdoctoral fellows, graduate students, undergraduate researchers, high school science teachers and high school students on the research team. X-ray powder diffraction workshops organized through this project are training the next-generation workforce to solve complex scientific problems with the use of advanced research tools. Outreach activities geared toward women, minorities and economically disadvantaged students are taking place through the research group's participation in the ACS Project SEED program and interactions with local undergraduate women in STEM fields.<br/><br/><br/>Technical Abstract<br/>Current commercially available infrared nonlinear optical crystals have shortcomings, such as a lack of power-handling ability and multiphoton absorption effects that preclude usage with high-powered lasers and operation at certain wavelengths, respectively. This project, supported by the Solid State and Materials Chemistry program, focuses on the synthesis and characterization of quaternary diamond-like semiconductors and the assessment of their potential as new infrared nonlinear optical materials. Nonlinear optical (NLO) properties on powdered diamond-like semiconductor samples and additional properties of centimeter-sized single crystals are being assessed. The powdered/microcrystalline compound samples are prepared by high-temperature solid-state or lithium polysulfide flux synthesis. Second-order nonlinear optical susceptibility, laser damage threshold and the onset wavelength for phase matchability, as well as transparency range and bandgap are being measured. The preparation of centimeter-scale single crystals of selected compounds identified as promising candidates is being carried out via the vertical Bridgman method and iodine-vapor transport reactions. Certain properties of technological importance, including thermal conductivity and extreme optical transparency measured by laser calorimetry, are being assessed using these sizeable single crystals. Relationships between the composition, crystal structure and electronic structure of the materials, especially bandgap, and the observed physical properties are being considered to build crystal-chemical concepts that allow for knowledge-based optimization of materials' NLO properties.
