Fantastic achievements in present-day electronics are based on detailed knowledge of the properties of silicon doped with phosphorus and boron. Similar knowledge of physical properties of optical materials doped with rare-earth and transition ions is required for the fast and successful development of optoelectronics devices, for instance, laser screens suitable for a use by the bright sun light on streets, highways and airports. This project will be devoted to the investigation of intentionally doped optical crystals with the help of techniques, which operate at different frequencies of electromagnetic waves (multifrequency spectroscopy). It is expected that this research will give a significant contribution to the fundamental understanding of the nature, properties and interrelation of defects created by doping, determination of their structures on atomic/nanoscale levels, and finally, to tailoring properties of optical materials. This is of key importance for optical communication technologies. Conducting cutting-edge investigations, students and post-docs will become proficient in state-of-the art experimental techniques; learn promising materials and their potential applications. All these will improve their career prospects and efficiency of their future activity.
Doping materials like lithium niobate and tantalate allows creating various elements for optoelectronics: waveguides, modulators, lasers, fiber amplifiers, holographic memory etc. Electrical and magnetic interactions of transition and rare earth ions with surrounding ions have frequencies from kilohertz up to petahertz. Complementary techniques including electron paramagnetic resonance, electron nuclear double resonance, and optical spectrometers will be used in order to characterize these interactions and to clarify structures of impurity and intrinsic defects on atomic/nanoscale levels. It is expected that this research will give a significant contribution to the fundamental understanding of the nature, properties and interrelation of these defects, and finally, to tailoring properties of optical materials. Findings of the project will have a potential impact on various scientific projects, as well as on applications in optical communication technologies. Conducting cutting-edge investigations, students and post-docs will become proficient in state-of-the art experimental techniques, learn promising materials and their modern applications, and consolidate knowledge obtained in solid state physics courses.
Atomic size defects can be harmful (like defects created by aging or radiation) or useful (like boron and phosphorus dopants in Si, which create p- and n-type conductivity – the background of semiconductor devices). They govern often important properties of materials. Without such defects it would be no computers, lasers, cell phones and other useful things. However, we cannot see them by naked eyes or even with the help of optical microscopes. Lithium Niobate doped with transition and rare-earth ions is of great interest for both fundamental science and advanced applications including high efficiency lasers with frequency conversion, elements of all-optical telecommunication network and quantum cryptography. Sophisticated indirect methods - Electron Paramagnetic Resonance, EPR and Electron-Nuclear Double Resonance, ENDOR provide qualitative and quantitative information about impurity centers and their structures on the atomic level. Using EPR and ENDOR our group found, identified and characterized several new atomic defects in lithium niobate crystals doped with Fe, Nd, Er, Yb, Ho, and Rh. Our EPR/ENDOR study has shown that transition and rare-earth ions create unexpected variety of completely different non-equivalent centers in both stoichiometric and lithium deficient congruent crystals. Four neodymium, two erbium, and nine ytterbium centers were found and described. Dominant neodymium and ytterbium centers have distant charge compensation, whereas the charge excess in low-symmetry erbium centers is compensated by intrinsic defects in nearest surrounding. Ytterbium ions can also create self- compensated pairs substituting both lithium and niobium ions even at very low ytterbium concentration. An addition of rhodium to the melt facilitates entering other impurities to the grown crystals. Obtained fundamental understanding of the structures and properties of impurity defects in lithium niobate can be used for the "defect engineering" and tailoring properties of optical materials. The obtained numerous spectroscopic parameters can be placed in databases and used as cornerstones for model calculations of structural properties of crystals. Six undergraduate and two graduate students got training in experimental technique (magnetic resonance and optical spectrometers, vacuum and cryogenic equipment) conducting described research. At present, one graduate student has successfully defended master thesis, three undergraduate students were accepted to graduate school, and three others plan to apply. Last year, the magnetic resonance spectroscopy was integrated to education program of the Physics Department as a part of the course "Advanced Experimental Physics Lab". Eleven students attended this course and carried out EPR measurements of selected samples using spectroscopic equipment of our lab. Backgrounds of magnetic resonance were placed on corresponding pages of the D2L (Desire To Learn) online system. The conducted research contributed also to lectures devoted to non-linear optical materials, ferroelectrics, photonic materials and magnetic properties of solids in the required course "Solid State Physics" for undergraduate students, "Novel Materials for Physics and Engineering" for graduate and undergraduate students, and "Condensed Matter Physics" for graduate students. Basic ideas of the EPR/ENDOR and combined multifrequency spectroscopy were presented in the popular lecture "How to See the Invisible", designed for undergraduate students. A part of our findings was already published in peer-review physics journals and presented at local, national and international scientific conferences; other results submitted are prepared for publications. Information about our activity, key results, publications and presentations was placed on our laboratory website: www.physics.montana.edu/eprlab/index.html The website was designed in a format, which is understandable for broad public and senators. Every year the website has been visited more than thousand times. It is supposed that pictures, animations and research materials placed on this website will attract new students and visitors.
