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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
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.