The role of sodium fluoride on CdO-B 2 O 3 glasses doped with chromium ions

The glass system x NaF-(40- x ) CdO-59.75B 2 O 3 -0.25Cr 2 O 3 (where x = 5, 10, 15, 20, 25, 30, 35 mol%) have been synthesized by conventional melt quenching technique. The prepared glasses were characterized by XRD, EPR, UV–VIS and FTIR spectroscopic techniques. The absence of sharp peaks in XRD spectra is the testimony for the amorphous nature of prepared glass samples. On replacing high crystal density CdO with low crystal density NaF in the glass composition resulted in decrease of density and increase of molar volume ( V m ). From optical absorption spectra three characteristics transitions 4 A 2g → 4 T 1g , 4 A 2g → 4 T 2g , 4 A 2g → 2 E g (G) were observed. Racah parameters D q , B , D q / B and C were evaluated. Optical band gap ( E g ), refractive index ( n ), Urbach energy (Δ E ), molar refraction ( R m ), molar electronic polarizability ( α m ) were evaluated. Optical band gap values were increasing it may be due to decrease of non bridging oxygen’s. Δ E is varying non-linearly whereas R m and α m were found to increase with increase of NaF. Using EPR spectra, g tensor values are evaluated and are attributed to exchange coupled pairs of Cr 3+ ions at low filed region while high field side is assigned to presence of Cr 3+ ions in the rhombic sites of strong crystal field. Sharp peak observed in FTIR spectra, around 1400 cm −1 is due to trigonal BO 3 units of pyroborate group. Four-coordinated boron atoms (N 4 ) were evaluated.