Cr-doped GdScO₃ single crystals were grown by the EFG method. Based on their absorption and emission spectras, the crystal field strength and the crystal field parameters of the octahedrally-coordinated Cr³⁺ ions were determined: Dq = 1553 cm^-1, B = 574 cm^-1, C = 3211 cm^-1, and Dq/B = 2.71 for 0.5% Cr:GdScO₃. Effective phonon energy was calculated to be 412 cm⁻¹, and the Huang–Rhys factor was 3.0. The emission spectra of Cr³⁺ doped GdScO₃ crystal covered the region from 650 nm to 1100 nm, and the emission cross-section at 767 nm was calculated to be 0.32×10⁻²⁰ cm². In comparison with the other Cr³⁺ doped materials, the Cr:GdScO₃ crystal has a short fluorescence lifetime, it can be used as a potential tunable laser gain medium.

In this paper, we report the fabrication of high-quality 5 at. % Er³⁺ ions doped SrF₂ transparent ceramics, the potential candidate materials for a mid-infrared laser-gain medium by hot-pressing at 700 °C for 40 h using a chemically-derived powder. The phase structure, densification, and microstructure evolution of the Er:SrF₂ ceramics were systematically investigated. In addition, the grain growth kinetic mechanism of Er:SrF₂ was clarified. The results showed lattice diffusion to be the grain growth mechanism in the Er:SrF₂ transparent ceramic of which highest in-line transmittance reached 92% at 2000 nm, i.e., very close to the theoretical transmittance value of SrF₂ single crystal. Furthermore, the emission spectra showed that the strongest emission band was located at 2735 nm. This means that it is possible to achieve a laser output of approximately 2.7 μm in the 5 at. % Er³⁺ ions doped SrF₂ transparent ceramics.

Tm:LuYO3 mixed ceramic was successfully fabricated by the solid-state reactive sintering method. The absorption cross section and emission cross section were studied at room temperature. The fluorescence lifetime of 3F4 energy level was fitted to be 2.6 ms. A continuous-wave (CW) laser operation of Tm:LuYO3 ceramic, pumped at 796 nm, was realized with the output power of 1.2 W and slope efficiency of 25.1%. A mode-locking (ML) laser operation of Tm:LuYO3 ceramic was demonstrated for the first time with pulse duration of 41 ps and pulse repetition frequency of 139.3 MHz.

Lutetium aluminum garnet single-crystal fiber (SCF, ∼ Φ 0.9 mm – 165 mm) doped with 0.5 at.% Ho³⁺ has been grown by the micro-pulling-down (µ-PD) technique. The room-temperature absorption and emission spectra exhibit similar features to the bulk crystal. Laser performances of the SCFs with two different pump configurations, i.e., pump guiding and free-space propagation, are studied by employing a 1.9-µm laser diode and a high-brightness fiber laser, respectively. Laser slope efficiencies obtained with both pump configurations can be higher than 50%, and a maximum output power of 6.01 W is achieved at ∼ 2.09 µm with the former pump. The comparable efficiency to the high-brightness pump is an indication of that high laser performance can also be expected through pump-guiding in the SCF even with a low pump beam quality.

Pr³⁺-doped GdScO₃ single crystal was successfully grown by the Czochralski (Cz) method. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. The polarized spectroscopic property of Pr:GdScO₃ crystal for new-wavelength transition in the near infrared (NIR) region was discussed for the first time. The absorption cross-sections at 600 nm were calculated to be 0.39×10⁻²⁰ cm² (E∥a), 0.32×10⁻²⁰ cm² (E∥b) and 0.4×10⁻²⁰ cm² (E∥c). The emission cross sections at 1053 nm of ¹D₂ energy level were calculated to be 0.86×10⁻²⁰ cm² (E∥a), 0.79×10⁻²⁰ cm² (E∥b) and 0.78×10⁻²⁰ cm² (E∥c), with FWHM of 57.54 nm, 57.96 nm and 58.96 nm, respectively. The fluorescence lifetime and radiative lifetime of the ¹D₂ energy levels of Pr³⁺ ions were 45.46 µs and 393.94 µs, respectively. Those results show that the Pr:GdScO₃ crystal should be the potential near infrared laser gain medium originated from the ¹D₂ transition.

A ${\mathrm{Nd}}^{3+}$-doped ${\mathrm{LaMgAl}}_{11}{\mathrm{O}}_{19}$ (Nd:LMA) crystal was grown by the Czochralski method. Room temperature polarized absorption spectra, fluorescence spectra, and fluorescence lifetime of the Nd:LMA crystal were measured and analyzed. The Judd–Ofelt parameters ${\mathrm{\Omega }}_{2,4,6}$ were calculated to be $1.21\times {10}^{-20}$, $3.63\times {10}^{-20}$, and $2.35\times {10}^{-20}{\mathrm{cm}}^2$, respectively. The absorption and emission cross sections were calculated. Using a 790-nm diode laser as pump source, continuous-wave laser operation of an $a$-cut Nd:LMA crystal has been demonstrated with a maximum output power of 1.71 W and slope efficiency of 40.4% for a 1055 nm laser. Low-gain laser operation at 1082 nm is also realized with a maximum output power of 1.46 W and slope efficiency of 34.5%.