Investigation of the bioactivity, structural, optical and photoluminescence properties of ZnO-doped borate bioactive glass

A series of bioactive glasses with composition xZnO−(65−x)B2O3−6P2O5−11SiO2−11CaO−6Na2O−1Gd2O3 (x = 0−20 mol%) was prepared by the melt quenching technique, to investigate its bioactivity, structural, optical and photoluminescence properties. The bioactivity of the glass samples was evaluated by immersing the samples in phosphate buffer saline (PBS) solution for 7 and 14 days. The existence of a prominent peak at around 32° from XRD patterns and the presence of P−O bending of PO43- group around 560 cm−1 in FTIR spectra confirmed the formation of hydroxyapatite layer. The structural analysis revealed that the increase of ZnO content led to a decrease in N4 value, indicates a greater conversion of BO4 to BO3 unit and enhances the depolymerization. The incorporation of ZnO with B2O3 (x≥ 5 mol%) showed a decrease in both indirect and direct bandgap, which was attributed to the increased number of non-bridging oxygen. The incorporation of ZnO was found to enhance the emission intensity at 312 nm (6P7/2 → 8S7/2 transition) up to 1.09 × 107 a.u. (x = 20 mol%) and 1.11 × 107 a.u. (x = 15 mol%) for 7 and 14 days of immersion, respectively. This enhancement is attributed to the structural modifications in the glass network, which reduce non-radiative pathways and facilitates better transition in Gd3+ ions. However, the prolonged immersion caused a decrease in intensity due to an increase in the number of OH groups, which coupled with Gd3+ ions, thereby increase non-radiative pathways. Among the studied samples, the sample with x = 15 mol% of ZnO content exhibits the optimum photoluminescence intensity. These finding suggests that ZnO doped bioactive glass showing promising properties for biomedical and luminescence applications.

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