Growth, spectroscopy and laser operation of Tm,Ho:GdScO₃ perovskite crystal

We report on the growth, polarized spectroscopy and first laser operation of an orthorhombic (space group Pnma) Tm³⁺,Ho³⁺-codoped gadolinium orthoscandate (GdScO₃) perovskite-type crystal. A single crystal of 3.76 at.% Tm, 0.35 at.% Ho:GdScO₃ was grown by the Czochralski method. Its polarized absorption and fluorescence properties were studied revealing a broadband emission around 2 µm. The parameters of the Tm³⁺ ↔ Ho³⁺ energy transfer was quantified, P₂₈ = 1.30 × 10^-22 cm³µs^-1, and P₇₁ = 0.99 × 10^-23 cm³µs^-1, and the thermal equilibrium lifetime was measured to be 3.5 ms. The crystal-field splitting of Tm³⁺ and Ho³⁺ multiplets in Cs symmetry sites of the perovskite structure was determined by low-temperature spectroscopy and the mechanism of spectral line broadening is discussed. The continuous-wave Tm,Ho:GdScO₃ laser generated 1.16 W at ∼2.1 µm with a slope efficiency of 50.5%, a laser threshold of 184 mW, a linear laser polarization (E || c) and a spatially single-mode output. The Tm,Ho:GdScO₃ crystal is promising for broadly tunable and femtosecond mode-locked lasers emitting above 2 µm.