High‐Refractive‐Index La ₂ O ₃ –Nb ₂ O ₅ –WO ₃ Ternary Glasses Prepared Using a Levitation Technique

ABSTRACT Colorless and transparent La ₂ O ₃ –Nb ₂ O ₅ –WO ₃ (LNW) glasses were successfully synthesized using a levitation technique in a wide glass‐forming region. These glasses exhibited excellent optical properties, including a high refractive index (>2.1) with low wavelength dispersion, and high transmittance (70%‒75% at a thickness of ∼800 µm) in the ultraviolet–visible region. The glass transition temperature decreased with increasing WO ₃ content, reaching as low as 550°C, which enables easier pressing and molding compared to other levitation‐synthesized high‐refractive‐index glasses, such as Nb ₂ O ₅ ‐based and TiO ₂ ‐based glasses. The dependence of the packing density and the electronic polarizability of the oxide ion on the Nb ₂ O ₅ content suggested that the effect of substituting Nb ₂ O ₅ with WO ₃ substantially differs between La ₂ O ₃ ‐rich and Nb ₂ O ₅ ‐rich La ₂ O ₃ –Nb ₂ O ₅ binary glasses. The inherent absorption wavelength decreased with increasing WO ₃ content, resulting in a lower wavelength dispersion of the refractive index. These findings indicate that LNW glasses are promising optical materials for advanced applications requiring high refractive index and low processing temperature.