The Prospects of Tm ³⁺ ‐Doped Cubic Gadolinia and Its Solid Solutions for 2 µm Ceramic Lasers

This work investigates Tm 3+ ‐doped sesquioxide ceramics based on gadolinia and its binary and ternary solid solutions with yttria and lutetia as promising gain media for ∼2 µm lasers. Transparent ceramics containing 3 at.% Tm 3+ were fabricated by hot pressing of solid‐solution nanopowders. Their thermal conductivity systematically decreases with increasing compositional complexity, consistent with enhanced phonon scattering in multicomponent lattices. At 298 K, the thermal conductivity ranges from 8.6 W·m −1 ·K −1 for Tm:Gd 2 O 3 to 3.8 W·m −1 ·K −1 for the ternary (Tm 0.03 Gd 0.323 Y 0.323 Lu 0.323 ) 2 O 3 composition, while the linear thermal expansion coefficients lie between 4.7 and 6.6 ppm·K −1 . The addition of lutetia effectively suppresses grain growth: (Tm 0.03 Gd 0.485 Lu 0.485 ) 2 O 3 and (Tm 0.03 Gd 0.323 Y 0.323 Lu 0.323 ) 2 O 3 ceramics exhibit submicron average grain sizes, whereas the binary solid solution (Tm 0.03 Gd 0.485 Y 0.485 ) 2 O 3 shows coarser grains of about 7 µm in size. Spectroscopic studies reveal that the incorporation of smaller Gd 3+ cations weakens the crystal field around Tm 3+ ions, enabling controlled blue shifts of the emission peak down to 2050 nm compared with Sc 2 O 3 ‐, Y 2 O 3 ‐, and Lu 2 O 3 ‐based matrices. Compositional disorder in mixed‐cation lattices induces strong inhomogeneous broadening, yielding smooth and wide emission bands favorable for broadly tunable operation of ∼2 µm lasers.