Abstract
Calcium niobium gallium garnet (CNGG) crystals codoped with Yb3+, Ho3+ and Eu3+ ions were grown by the Czochralski method. The crystal structure (cubic, sp. gr. O10h - Ia3d, lattice constant a = 12.4748(2) Å) was refined by the Rietveld method. A Raman study revealed high-energy vibrations at 767–846 cm−1 due to the [Nb2|Ga2O4] groups. The spectroscopic properties of Yb,Ho: and Yb,Ho,Eu:CNGG crystals were studied with the goal of developing broadband emitting gain media around 2 μm and 3 μm. The maximum stimulated-emission cross-sections σSE are 0.57 × 10−20 cm2 at 2070 nm (the 5I7 → 5I8 Ho3+ transition) and 1.01 × 10−20 cm2 at 2869 nm (the 5I6 → 5I7 Ho3+ transition) and the emission spectra are smooth and broad owing to the structural disorder of the CNGG host matrix. The evidence of Yb3+(2F5/2) → Ho3+(5I6) energy transfer (ET) in the Yb,Ho:CNGG crystal is shown. Without Eu3+, the luminescence lifetimes of the 5I6 and 5I7 Ho3+ states are 0.30 ms and 7.24 ms, respectively. The Eu3+ codoping leads to the quenching of the 5I7 Ho3+ lifetime due to the Ho3+(5I7) → Eu3+(7F6) ET which is favorable for 3 μm laser operation. The crystal-field splitting of the Ho3+ multiplets is revealed at 12 K. First laser operation in Yb,Ho:CNGG crystals at 2.1 μm is achieved.
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