Department of Physics and Astronomy

University of Mississippi

Events

Event Information:

  • Tue
    18
    Oct
    2016

    Colloquia

    4:00 pmLewis Hall 101

    Chandrima Chatterjee
    Department of Physics and Astronomy
    University of Mississippi

    Experimental Investigation of Impurities and Their Effect on Acousto-Electric Properties of Lithium Niobate

    The functional parameters of Lithium niobate that is used in various acousto-opto-electronic applications are questionable. The nonclassical nonlinear effect such as “acoustical memory” is not explained at full. Despite there being publications on crystal defects in Lithium niobate, the relationship between the defects and Acoustical Memory has not yet been established. Previous publications analyzed the Acoustical Memory effect without going into the microstructural detail of the level of point defects. The purpose of this research is to establish a connection between the microscopic point defects and the macroscopic nonlinear phenomena. The present research aims at finding new crystal characteristics including the identification of impurities and point defects, the distribution of the defects along the optical crystallographic z axis, and in a direction normal to the z axis. Bulk crystals and wafers are studied. The impurities are identified by their characteristic lines in the photoluminescence spectra, which are taken at room temperature in a range of 350 to 900 nm. The spectra reveal the following point defects: Ar, Ba, Cs, F-color center, Rb, Ru, Sn, Fe, K, Li, O, Nb, Kr, NbLi4+, Xe, etc. The peak corresponding to the F-center is found at 400.429 nm and has the highest number of photon counts. Further, the samples are shifted with a step of tens of microns along the z-axes or normal to it. This optical scanning allows to find a distribution of the impurities in the samples. The photon counts changes with crystal position for some impurities. The distribution of these defects is observed as peaks and valleys. The results may be used to discover the physical mechanisms behind nonclassical nonlinear phenomena in Lithium niobate.