Float glass-type SiO ₂-Na ₂O-CaO glasses with 0 – 10 mol% Sb₂O₃ were melted and their compositional, structural, thermal and optical properties characterised. All glasses were X-ray amorphous and increasing Sb₂O₃ content progressively decreased glass transition temperature (T_g) and dilatometric softening point (T _d), despite increases in Al₂O₃ content from greater crucible corrosion. ¹²¹Sb Mössbauer spectroscopy confirmed that Sb was predominantly incorporated as Sb ³⁺ (Sb ³⁺/ΣSb ~ 0.9) and Raman spectroscopy showed that Sb substantially decreased average (Si, Al)-O Qⁿ speciation. Both techniques confirmed that Sb³⁺ ions were incorporated in trigonal pyramidal [:SbO ₃] polyhedra. XRF and Raman spectroscopies confirmed that SO ₃ content decreased with increasing Sb₂O₃ content. TGA analysis showed, as a linear function of Sb₂O₃ content, mass gain commencing at 700°C, reaching a maximum at 1175°C, then mass loss above 1175°C, consistent with oxidation (Sb³⁺ → Sb⁵⁺) then reduction (Sb⁵⁺ → Sb³⁺). The TGA samples were shown to have attained or approached Sb redox equilibrium during measurement. Optical absorption spectroscopy (UV-Vis-nIR) showed red-shifts of the UV absorption edge with increasing Sb ₂O ₃ content, consistent with increasing intensity of far-UV absorption bands from Sb³⁺ and Sb⁵⁺ s→p transitions. UV-Vis-nIR fluorescence spectroscopy evidenced a broad luminescence band centred at ~25,000 cm⁻¹, attributed to the ³P ₁→ ¹S ₀ transition of Sb ³⁺, which is Stokes shifted by ~15,000 cm ⁻¹ from the ¹S₀→ ³P₁ absorption at ~40,000 cm⁻¹. The most intense emission occurred at 0.5 mol% Sb ₂O₃, with concentration quenching reducing luminescence intensities at higher Sb ₂O₃ contents. Additions of Sb₂O₃ to float-type soda-lime-silica glasses could thus enable lower melting energies and/or new solar energy applications.