A holistic approach to Cr₂O₃-doped lithium lead borosilicate glasses: probing thermal stability, optical emissions, and gamma shielding

Abstract

A series of chromium oxide (Cr₂O₃)-doped lithium lead borosilicate glasses with the nominal composition (20−x)Li₂O+5PbO+15B₂O₃+60SiO₂+xCr₂O₃ ​ (where x = 0.00–0.5 mol%) were successfully synthesized via the conventional melt-quench technique. The structural, morphological, thermal, optical, and radiation shielding characteristics of these glasses were investigated using various advanced characterization techniques. X-ray diffraction (XRD) analysis confirmed the amorphous nature of all prepared samples, evidenced by the absence of sharp diffraction peaks. The broad humps observed in the XRD patterns were consistent with a disordered glass network, which remained intact upon Cr₂O₃ doping up to 0.50 mol%. Scanning electron microscopy (SEM) images revealed a homogeneous and dense glassy microstructure, with minor surface irregularities that slightly increased with higher Cr₂O₃ content, suggesting local compositional variation or microphase separation. Energy-dispersive X-ray spectroscopy (EDS) analysis validated the elemental composition and confirmed the successful incorporation of chromium into the glass matrix. Fourier-transform infrared spectroscopy (FTIR) studies indicated the presence of Si–O–Si, B–O–B, and B–O–Si linkages, with additional bands attributed to non-bridging oxygen (NBOs) and Cr–O vibrations appearing in the 550–700 cm⁻¹ region for doped samples. The increase in Cr₂O₃ concentration led to a slight shift and broadening of these bands, implying structural modifications in the glass network, likely due to the conversion of BO₃ to BO₄ units and increased NBO content. Raman spectroscopy further supported these findings by revealing a systematic evolution of vibrational modes associated with BO₃/BO₄ units and silicate groups. The progressive intensity changes in Cr-related modes suggest a shift in chromium coordination and interaction with the glass network. Differential thermal analysis (DTA) showed a gradual increase in the glass transition temperature (Tg) with Cr₂O₃ addition, indicative of enhanced network rigidity. However, at higher doping levels (≥0.3 mol%), a slight reduction in thermal stability was observed, potentially due to the clustering of Cr ions or partial crystallization tendencies. Radiation shielding properties were evaluated by calculating parameters such as linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), and half-value layer (HVL). The results demonstrated an improvement in gamma-ray attenuation ability with increasing Cr₂O₃ concentration, primarily due to the higher atomic number and density of Cr ions, which enhance photon interaction probabilities. Electron paramagnetic resonance (EPR) spectra confirmed the presence of Cr³⁺ ions in octahedral symmetry, with a prominent resonance signal around g ≈ 1.97. The increasing intensity and narrowing of the resonance lines with Cr₂O₃ content point to stronger Cr³⁺–Cr³⁺ dipolar interactions and possible clustering effects at higher doping levels. Optical absorption spectra exhibited characteristic Cr³⁺ bands, particularly in the UV–Vis region, attributed to electronic transitions such as ⁴A_2​g→⁴T₂​g and ⁴A_2g→⁴T_1g. The optical band gap energy (Eₒₚₜ) was found to decrease with increasing Cr₂O₃ content, indicating an increase in localized states and the formation of NBOs within the glass matrix. Photoluminescence (PL) spectra displayed broad emission bands in the red–near infrared region, centered around 700–750 nm, corresponding to the ⁴T_2​g→⁴A_2​g transitions of Cr³⁺ ions. The emission intensity initially increased with Cr doping up to 0.2 mol% due to efficient energy transfer and optimum dispersion of Cr³⁺ ions, followed by quenching at higher concentrations due to concentration quenching and cross-relaxation effects. In summary, Cr₂O₃ doping induces significant structural rearrangements and enhances the optical and radiation shielding capabilities of Li₂O–PbO–B₂O₃–SiO₂ glasses. The sample with 0.2 mol% Cr₂O₃ (LiCr-0.25) exhibited the most balanced combination of thermal stability, photoluminescence efficiency, and shielding performance, making it a promising candidate for optoelectronic and radiation protection applications.