Fabrication and luminescent properties of highly transparent novel high-entropy (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic

The highly transparent novel high-entropy (Lu 0.2 Y 0.2 Gd 0.2 Yb 0.2 Er 0.2 ) 2 O 3 ceramic was successfully fabricated by the addition of 3 at.% ZrO 2 and 10 at.% La 2 O 3 introduced as sintering additives via vacuum sintering. A single-phase solid solution cubic structure of the ceramic was obtained with a relative density of 99.95 % and an average grain size of 6.91±3.28 µm. The grain boundary of the (Lu 0.2 Y 0.2 Gd 0.2 Yb 0.2 Er 0.2 ) 2 O 3 ceramic was clean with a thickness of only 1.3 nm. Further observations revealed uniform distribution of all elements in the grains, and the presence of La and Zr segregation (1.5 nm thick) at few grain boundaries, but causing very little light scattering. The in-line transmittance of high-entropy (Lu 0.2 Y 0.2 Gd 0.2 Yb 0.2 Er 0.2 ) 2 O 3 ceramic reached 80 % at 1100 nm, which was 98.7 % of the theoretical value of Er 2 O 3 single crystal. Also, there were fluorescence emissions observed in the ultraviolet (311 nm), visible (563, 622 nm), and near-infrared (1032, 1535 nm) regions. In addition, the intense red emission and weak green emission were detected, and the broad emission with a peak at 1.5 μm was attributed to Stark splitting of Er 3+ ions, so the corresponding mechanism was discussed. Results obtained suggest that the highly transparent novel high-entropy (Lu 0.2 Y 0.2 Gd 0.2 Yb 0.2 Er 0.2 ) 2 O 3 ceramic fabricated in this study could have broad application prospects in optical applications such as scintillators, up-conversion luminescent materials, and infrared lasers.