Optical band gap studies on lithium aluminum silicate glasses doped with Cr3+ ions

Abstract

Lithium aluminum silicate glass system (LAS) implanted with chromium ions is prepared. The reflectance and transmittance measurements are used to determine the dispersion of absorption coefficient. The optical data are explained in terms of the different oxidation states adopted by the chromium ions into the glass network. It is found that the oxidation state of the chromium depends on its concentration. Across a wide spectral range, 0.2–1.6μm, analysis of the fundamental absorption edge provides values for the average energy band gaps for allowed direct and indirect transitions. The optical absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. Such tail is decreased with the increase of the chromium dopant. From the analysis of the optical absorption data, the absorption peak at ground state exciton energy, the absorption at band gap, and the free exciton binding energy are determined. The extinction coefficient data are used to determine the Fermi energy level of the studied glasses. The metallization criterion is obtained and discussed exploring the nature of the glasses. The measured IR spectra of the different glasses are used to throw some light on the optical properties of the present glasses correlating them with their structure and composition.

EPR, optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses

“…It is verified that the optical band gap decreases (red shift) with an increase of the Cr 3+ doped into the SbPO glasses. Our result agrees with that reported by Kesavulu et al [18] and El-Diastya et al [32]. This is attributed to the Cr 3+ doping which creates localized levels close to the conduction band of antimony phosphate glass.…”

“…These localized levels interact with the conduction band, resulting in their subdivision and reducing the band gap. Additionally, lower values of E opt with increasing concentration of Cr 3+ are evidence of changes from covalent to less covalent (more ionic) bonds, related also with the higher concentration of nonbridging oxygens (NBOs) due to the incorporation of chromium ions, causing a depolymerization of the phosphate network [32].…”

EPR, optical absorption and photoluminescence properties of Cr3+ ions in lithium borophosphate glasses

“…It is observed that the optical band gap decreases with increase in concentration of chromium content. This observation must be attributed to the network structural differences brought by the additional presence of chromium ions [39].…”

Synthesis and characterization of low cost willemite based glass–ceramic for opto-electronic applications

“…In addition, optical band gap decreases for glass-ceramics crystallized at higher temperatures. This reduction is due to the decrease in average bond energy and fall in conduction band's level, which arose from creation of NBO's [41]. On the other hand, the reduction in band gap energy could be interpreted by assuming the production of surface dangling bonds around crystallites during the process of crystallization [42].…”