Development of Quaternary Diamond-like Semiconductors for Infrared Nonlinear Optical Applications

非线性光学（NLO）晶体用于将激光器的相干单色光转换为其它所需波长。红外非线性光学应用包括，远距离检测毒品和爆炸物，非侵入性医疗诊断和监测呼吸分析使用分子光谱和红外反措施系统用于保护军用飞机，仅举几例。然而，目前市售的用于红外非线性光学器件的晶体存在缺陷，并且缺乏限制其实际应用的关键领域。新的红外非线性光学材料的发现使医疗、工业和军事领域的新应用得以实现。此外，改进的红外非线性光学材料的合成允许更可靠、更持久的设备在这些材料已经发现实用性的领域中具有更大的影响。更好地理解晶体结构与其产生的性质之间的关系可以使该领域的进展更快。通过该项目，结构-性能相关性正在从四元金刚石类半导体的系统研究中发展出来，该研究将联合收割机战略实验与理论相结合，其中通过实验结果培养可靠预测性能的能力。这些结构-性质关系正在通过博士后研究员、研究生、本科生研究人员、高中科学教师和研究团队中的高中生的研究努力来揭示。通过该项目组织的X射线粉末衍射讲习班正在培训下一代劳动力，以使用先进的研究工具解决复杂的科学问题。通过参与ACS Project SEED项目以及与STEM领域的当地女大学生的互动，面向女性、少数民族和经济困难学生的外展活动正在进行。技术摘要目前市售的红外非线性光学晶体存在缺点，例如缺乏功率处理能力和多光子吸收效应，这分别妨碍了高功率激光器的使用和在某些波长下的操作。该项目由固态和材料化学计划支持，重点是四元类金刚石半导体的合成和表征，以及评估其作为新型红外非线性光学材料的潜力。正在评估粉末状金刚石半导体样品的非线性光学（NLO）特性和厘米级单晶的其他特性。粉末/微晶化合物样品通过高温固态或多硫化锂助熔剂合成制备。测量了薄膜的二阶非线性极化率、激光损伤阈值、相位匹配起始波长、透明范围和带隙。目前正在通过垂直布里奇曼法和碘蒸气传输反应制备被确定为有希望的候选化合物的厘米级单晶。某些具有技术重要性的特性，包括通过激光量热法测量的热导率和极端光学透明度，正在使用这些相当大的单晶进行评估。材料的组成、晶体结构和电子结构（特别是带隙）与观察到的物理性质之间的关系正在被考虑以建立晶体化学概念，从而允许基于知识的材料NLO性质的优化。

Non-Technical AbstractNonlinear 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.Technical AbstractCurrent 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.