Spectroscopy of solid-solution transparent sesquioxide laser ceramic Tm:LuYO ₃

We report on a detailed spectroscopic study of a Tm ³⁺ -doped transparent sesquioxide ceramic based on a solid-solution (lutetia – yttria, LuYO ₃ ) composition. The ceramic was fabricated using commercial oxide powders by hot isostatic pressing at 1600°C for 3 h at 190 MPa argon pressure. The most intense Raman peak in Tm:LuYO ₃ at 385.4 cm ^-1 takes an intermediate position between those for the parent compounds and is notably broadened (linewidth: 12.8 cm ^-1 ). The transition intensities of Tm ³⁺ ions were calculated using the Judd-Ofelt theory; the intensity parameters are Ω ₂ = 2.537, Ω ₄ = 1.156 and Ω ₆ = 0.939 [10 ²⁰ cm ² ]. For the ³ F ₄ → ³ H ₆ transition, the stimulated-emission cross-section amounts to 0.27 × 10 ⁻²⁰ cm ² at 2059nm and the reabsorption-free luminescence lifetime is 3.47 ms (the ³ F ₄ radiative lifetime is 3.85 ± 0.1 ms). The Tm ³⁺ ions in the ceramic exhibit long-wave multiphonon-assisted emission extending up to at least 2.35 µm; a phonon sideband at 2.23 µm is observed and explained by coupling between electronic transitions and the dominant Raman mode of the sesquioxides. Low temperature (12 K) spectroscopy reveals a significant inhomogeneous spectral broadening confirming formation of a substitutional solid-solution. The mixed ceramic is promising for ultrashort pulse generation at >2 µm.