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Centennial Honors College Western Illinois University Undergraduate Research Day 2014 Poster Presentation Variation Of Optical Band Gap In Lead And Bismuth Borate Glasses Tyler J. Czarnecki Faculty Mentors: P.K. Babu and Saisudha B. Mallur Physics The study of variation of optical band gap with composition in oxide glasses gives information regarding the structure and the nature of bonds in the matrix. The width of the localized states in the band gap which arises due to the disorder in the matrix can also be determined. We studied the variation of optical band gap as a function of glass composition in lead and bismuth borate glasses. Glasses are prepared by the usual melt quench method for various amounts of lead and bismuth oxides. The as-prepared glass samples are then annealed at 400 oCfor 3 hours to remove thermal strains. Theannealed glass samplesarepolished using a felt pad sander.Optical absorption measurements are carried out on these samples using a UV-VIS absorption spectrometer. The experiment is done in the absorption mode, where the polished glass sample is placed in the path of electromagnetic radiation from the excitation source. The absorption edge data is then analyzed in detail to obtain the optical band gap of the glass samples.The experimental value of the band gap is used to determine the type and nature of the optical transition. Overall the band gaps of the Bi2O3glassesare smaller than those of PbO glasses. Our results show that in both lead and bismuth borate glasses, the optical band gap decreases with increasing concentration of PbO/Bi2O3. Our analysis also showed that these are indirect allowed transitions (n = 2).Variations in band gaps can be attributed to the structural and chemical changes that accompany the variation in glass composition.