Highly dense translucent CeO _2‒ <i> _δ </i> ·(RE, Y, Sm, La) ₂ O ₃ (RE = Dy, Gd) high‐entropy ceramics for multi‐wavelength emission

Abstract This study reports the synthesis of translucent, high‐entropy oxide (HEO) ceramics with the composition CeO 2‒ δ ·(RE, La, Sm, Y) 2 O 3 (RE = Dy, Gd), and a single‐phase bixbyite structure (space group Ia‐3). The materials were prepared by reactive sintering at 1600°C in air, achieving translucency through optimized ball milling of precursor oxides and refinement of processing parameters. X‐ray diffraction and scanning electron microscopy confirmed phase purity and a highly dense microstructure, with relative densities exceeding 99%. The samples were translucent in the visible and near‐infrared part of the spectrum. To improve the transparency, hot isostatic pressing (HIP) at 1600°C and 185 MPa was employed on the samples sintered for 6 h. HIP induced partial phase separation, impairing translucency. The effect of dwell time on luminescence properties of reactive sintered samples was also studied. Ultraviolet‒visible spectroscopy revealed a narrower bandgap and an enhanced photoluminescence (PL) intensity in the sample sintered for 6 h, as a result of a higher concentration of oxygen vacancies. PL under 302 nm excitation displayed multi‐wavelength emissions peaking at 432, 572, and 653 nm, producing near‐cold white light. Time‐resolved PL decay analysis indicated multiple luminescence centers with efficient energy transfer (e.g., Ce 3+ to Sm 3+ /Dy 3+ /Gd 3+ ).