Fabrication and spectroscopy of a high-entropy mixed sesquioxide (Er_0.2Lu_0.2Y_0.2Sc_0.2Gd_0.2)₂O₃ crystal fiber

A high-entropy (Er 0.2 Lu 0.2 Y 0.2 Sc 0.2 Gd 0.2 ) 2 O 3 mixed sesquioxide crystal fiber was grown by the laser-heated pedestal growth (LHPG) method. X-ray diffraction (XRD) confirmed that (Er 0.2 Lu 0.2 Y 0.2 Sc 0.2 Gd 0.2 ) 2 O 3 exhibits a single-phase cubic structure. Detailed investigations have been conducted on its absorption spectrum, fluorescence spectrum, and fluorescence lifetime. Judd-Ofelt ( J-O ) analysis was performed to calculate the spontaneous emission probabilities, branching ratio, and the radiative lifetime. The absorption cross-section at 981 nm was calculated to be 3.11 × 10 −21 cm 2 . The emission cross section of 4 I 11/2 → 4 I 13/2 transition at 2720 nm was 0.19 × 10 −20 cm 2 with the full width at half maximum (FWHM) of 45.3 nm. The effects of structural disorder and lattice distortion contribute to the non-uniform broadening of the spectrum. The fluorescence lifetimes of the upper ( 4 I 11/2 ) and lower ( 4 I 13/2 ) laser levels were determined to be 0.16 and 0.42 ms, respectively. All the results demonstrate the high potential of Er 3+ -doped high-entropy mixed sesquioxide for tunable and ultrafast laser generation in the mid-infrared range.