Structure, Optical Properties, and Electronic Structure of (Y _0.95 − <i> _x </i> Sc <i> _x </i> Yb _0.05 ) ₂ O ₃ Sesquioxide Transparent Ceramics

ABSTRACT Transparent sesquioxide ceramics of (Y 0.95 − x Sc x Yb 0.05 ) 2 O 3 ( x = 0–0.33) were synthesized by vacuum pressure‐less sintering to explore the effects of Sc substitution on the structure, optical properties, and electronic structure. Among all compositions, the (Y 0.7 Sc 0.25 Yb 0.05 ) 2 O 3 sample achieves the highest transmittance, reaching 81.4%@600 nm. With the introduction of Sc 2 O 3 , the emission spectra of (Y 0.95 − x Sc x Yb 0.05 ) 2 O 3 transparent ceramics exhibit pronounced inhomogeneous broadening. At x = 0.25, the full width at half maximum (FWHM) increases by 34.47% compared with that at x = 0, indicating that this material is a highly promising gain medium for ultrafast laser applications. DFT calculations show that Sc 3+ and Yb 3+ ions preferentially occupy S 6 ‐sites, and the saturation of these sites at x = 0.25 gives rise to a band‐gap extremum. Further Sc substitution forces occupation of C 2 ‐sites, increasing structural disorder and leading to the non‐monotonic variation of the band gap. Electron localization function (ELF) and Bader charge analyses confirm the predominantly covalent nature of the Y─O bonds. Furthermore, optical property simulations demonstrate that with increasing Sc content ( x ), the spectra exhibit a redshift and a gradual decrease in intensity, attributed to Sc‐induced lattice distortion and crystal field splitting.