Transparent ceramics for high-power infrared lasers operating above μm

Solid-state lasers are a key part of advanced devices and great efforts has devoted to improving their performance, including the research of novel materials as a powerful alternative to conventional glass or single-crystals. We demonstrated a versatile sol-gel approach to nanocrystalline $\left(\mathrm{Ho}_{0.03} \mathrm{La}_{0.97}\right)_{2} \mathrm{Zr}_{2} \mathrm{O}_{7}$ thin films. We proved $\mathrm{Ho}^{3+}$ ions regularly substituted $\mathrm{La}^{3+}$ ions in the host matrix. The residual -OH groups were presented in the samples bonded on $\mathrm{La}^{3+}$ ions. The highest phonon energy was $653 \mathrm{~cm}^{-1}$ allowing the luminescence up to 3.06 μm. The film of the thickness of 380 nm showed a refractive index of 2.28 at a wavelength of 632 nm. The sample showed luminescence spectra characteristic for $\mathrm{Ho}^{3+}$ ions. The emission maximum was observed for the electronic transition ${ }^{5} \mathrm{I}_{7} \rightarrow{ }^{5} \mathrm{I}_{8}$ at 2.1 μm. The luminescence intensity of the electronic transition ${ }^{5} \mathrm{I}_{6} \rightarrow{ }^{5} \mathrm{I}_{7}$ at 2.9 μm reached 7% of the maxima. The luminescence decay time recorded at 2.1 μm and 2.9 μm was 6.814 ms and 0.565 ms, respectively. High thermal and chemical stability of proposed materials, together with advanced processing methods open new horizons in technology of the mid-infrared active waveguides and fibers with improved lasing efficiency and stability.