The Melt-quench method is used to synthesize zinc fluoroborate glasses with compositions ( , 5, 10, 15, and 20). Optical characterization was carried out to examine the variation of optical bandgap energy ( ) and urbach energy ( ) with respect to the concentration for the samples annealed at different temperatures ( , and ). Annealing shows its effect on the samples with the variations in the values of and . These variations are explained on the basis of formation of different molecular species like units, boroxol rings, and the change in the number of nonbridging oxygen atoms. 1. Introduction Crystallization of a melt can be avoided by a sufficient fast cooling rate to form the amorphous phase. In borate glasses, boron-oxygen triangles bear sheet like structure with their ability to connect themselves to form a network. This characteristic has popularized B2O3 as one of the best glass formers [1, 2]. The requirement of random arrangement of various atomic and molecular species is easily fulfilled in borate glasses. With the addition of alkali halides in borate glasses there appears modifications in some properties of these glasses due to variations that occurred in their structures [3–9]. These modifications are reported for the inclusion of LiF in the borate glasses [3]. Some oxygen atoms get replaced by fluorine ions in the network to form new units like BO2F, BO2F2, BOF3, and BO3F [4–6]. There may be an increase in the number of nonbridging oxygen atoms due to the increase in polyhedral groups of boron and oxygen [7–9]. Modifications in microstructure of a substance are observed in terms of variations of various properties like optical, physical, electrical and structural, and so forth. Structure and therefore optical characteristics of a material are affected by nonhomogeneous cooling of the melt. The effect of annealing at different temperatures on optical and structural properties of B2O3 glasses is reported so far [10–14]. In these glasses, there is always a possibility of formation of B3O6 rings called boroxol rings, by the combination of BO3 groups. Raman spectroscopy reveals that for annealing temperature greater than the glass transition temperature, the concentration of boroxol rings increases with a decrease in temperature [13]. There appears a residual stress in such materials. During annealing of a glass, a thermodynamical and mechanical steady state is achieved after a specific time and temperature. This paper reports the effect of annealing at different temperatures on optical properties of ZnO LiF B2O3 glasses. With the addition of
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