Enhancement of structural and photoluminescence characterizations in Sm3+ and Cu2+-doped zinc bismuth borate glasses

Bismuth-based glasses have emerged as eco-friendly, lead-free alternatives for advanced optical and shielding applications. In this study, zinc–bismuth borate glasses with the nominal composition (30 − x )Bi 2 O 3 –30B 2 O 3 –40ZnO– x MO (where MO signifies Sm 2 O 3 or CuO, x = 0, 5 mol%) were synthesized via the melt-quenching technique. The investigation focused on the quantitative impact of Sm 2 O 3 and CuO doping on the physical, structural and spectroscopic properties of the matrix. The impacts on density, molar volume, structural, mechanical, and photoluminescence properties were extensively investigated. Examination methodologies included X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and ultrasonic velocity measurements. XRD analysis confirmed the amorphous nature of the synthesized glasses. FTIR spectra indicated an increase in the cross-link density of the Bi 2 O 3 –B 2 O 3 –ZnO network, evidenced by the emergence of [BO 4 ] units and an increased presence of [BiO 6 ] and [BiO 3 ] groups, which collectively enhanced the covalent character of the chemical bonds. Ultrasonic measurements revealed that both longitudinal and shear velocities increased with Sm 2 O 3 doping but decreased with the addition of CuO. This trend is attributed to the enhanced structural connectivity and rigidity induced by Sm 3+ ions. Consequently, mechanical properties (including elastic moduli, microhardness ( H u ), Poisson’s ratio, and Debye temperature) showed a significant improvement with Sm 2 O 3 substitution. A direct correlation was observed between microhardness and the softening temperature T s , the increase in T s with Sm 2 O 3 and CuO content indicates improved cross-linking and a reduction in non-bridging oxygen (NBO) atoms, aligning with density and FTIR data. Photoluminescence (PL) spectra obtained in the UV–Visible–NIR range exhibited four characteristic emission bands for Sm 2 O 3 -doped glass at 565, 602, 648, and 702 nm, corresponding to the 4 G 5/2 to 6 H 5/2, 7/2, 9/2, 11/2 transitions. Additionally, universal emission peaks were observed at 380 and 405 nm (Bi 3+ ions), 462 nm (band-edge excitation), 469 nm (Zn interstitials/vacancies), and 543 nm (oxygen vacancy defects). The enhancement in ultrasonic velocities was linked to the structural transition of boron from threefold (BO 3 ) to fourfold (BO 4 ) coordination, increasing network stiffness. Finally, PL intensity was significantly enhanced by Sm 3+ doping but showed a decrement with Cu 2+ incorporation. The outcomes demonstrate that Sm 2 O 3 doping greatly improves mechanical and optical properties, making these glasses acceptable for photonic purposes.