Abstract
Combined optical and FTIR spectroscopy has been employed to investigate the undoped NaF-CaF2-B2O3 glass together with samples containing 0.2% dopant of 3d TM ions before and after gamma irradiation. The optical spectrum of the undoped glass reveals strong UV absorption with two peaks which are related to unavoidable trace iron impurity within the raw materials. Upon gamma irradiation, an induced visible broad band centered at 500 nm is resolved and is related to B-O hole center or nonbridging oxygen hole center. TMs-doped samples exhibit characteristic absorption due to each respective TM ion but with faint colors. Gamma irradiation of TMs-doped samples reveals the same induced visible band at 500–510 nm in most samples except CuO and Cr2O3-doped glasses. Infrared absorption spectra reveal characteristic vibrational bands due to triangular and tetrahedral borate groups. The introduction of NaF and CaF2 modifies the borate network forming BO3F tetrahedra. The introduction of 3d TMs as dopants did not make any obvious changes in the FTIR spectra due to their low content (0.2%). Gamma irradiation causes only minor variations in the intensities of the characteristic IR borate bands while the bands at about 1640 cm−1 and 3450 cm−1 reveal distinct growth in most samples.
Highlights
Borate glasses belong to a valuable and interesting system which finds applications for optical, thermal, electrical, and biological purposes [1,2,3]
Optical absorption spectrum of undoped NaF-CaF2B2O3 glass reveals strong UV absorption bands which are attributed to trace iron (Fe3+) impurities
TMs-doped (0.2%) samples show characteristic absorption bands related to respective TM ions and they exhibit high valence states except in few cases (e.g., Ni and Co are only divalent ions)
Summary
Borate glasses belong to a valuable and interesting system which finds applications for optical, thermal, electrical, and biological purposes [1,2,3]. Upon the addition of an alkali oxide, alkaline earth oxide, or heavy metal oxide (e.g., PbO, Bi2O3, and Sb2O3) successive parts of BO3 groups are changed to BO4 groups until certain limit after which the excess additions of the mentioned oxides form nonbridging oxygens. Borate glasses unlike silicate and phosphate glasses possess rich chemistry where different structural groups or super structural units can be formed. The infrared spectra of structural vibrational groups belonging to BO3 or BO4 units have varying wavenumber positions. The BO4 groups are vibrating within the range 800–1200 cm−1 while the BO3
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