Novel Yb, Ho: NLGW Laser Crystal with Temperature Self-Monitoring Capability Achieved through Local Ligand Distortion Design

By introducing the sensitizing ion Yb3+ into the host lattice, the local ligand structure was optimized, resulting in improved luminescence efficiency of the active ions and enhanced thermal properties of the host material. A novel laser crystal material with temperature monitoring capability, 8 at. % Yb3+ and 1 at. % Ho3+: NaLa0.85Gd0.06(WO4)2, was successfully grown using the Czochralski method. X-ray rocking curve and Rietveld refinement analysis indicated that the grown crystal possesses high crystallinity and crystallizes in the I41/a space group, with lattice parameters of a = b = 5.3232 Å, c = 11.6019 Å, and V = 328.7610 Å3. The optical properties were characterized using absorption and near-infrared emission spectra, and the Judd–Ofelt (J-O) parameters were calculated to provide a theoretical foundation for subsequent laser output. Compared to the 1 at. % Ho3+: NaLa0.93Gd0.06(WO4)2 crystal, the introduction of the sensitizing ion Yb3+ led to a slight distortion of the host lattice, as shown by Fourier infrared spectroscopy, which increased the vibration of Yb–O bonds, significantly enhancing the luminescence efficiency. In addition to studying the basic energy transfer mechanism leading to enhanced luminescence, the relationship between the electron structure and local ligand distortion is explained for the first time, and the energy transfer mechanism of Yb–Ho is explained from two aspects. The thermal properties of the grown 8 at. % Yb3+ and 1 at. % Ho3+: NaLa0.85Gd0.06(WO4)2 laser crystal was studied. In the temperature range of 300–800 K, the crystal exhibited a low thermal expansion coefficient (8.138 × 10–6 K–1), indicating a higher likelihood of achieving excellent laser gain. Finally, the temperature sensing properties were investigated, showing a high Sr value of 1.18% K–1 at 303 K, suggesting that the prepared crystal not only has excellent self-detection capabilities but also holds great promise as an outstanding medium for 2 μm solid-state lasers.