Nd³⁺:YAG–Al₂O₃ nanocrystalline transparent ceramics with high inflexion concentration quenching of Nd³⁺ prepared by amorphous crystallization

Rare earth ion-doped Y₃Al₅O₁₂ (YAG)-based transparent ceramics have been used as important laser gain media for a long time, yet the doping concentration of active ions is limited due to concentration quenching, wherein the inflexion concentration quenching of Nd³⁺ is recognized as 1.0 at%. In this work, YAG–Al₂O₃ nanocrystalline transparent ceramics with a concentration of Nd³⁺ (0–5.0 at%) were fabricated via amorphous crystallization, and the crystal structure evolution, morphology, and optical properties were systematically investigated by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), magnetic resonation (MAS), nuclear magnetic resonation (NMR), and fluorescence spectroscopy. The doping of Nd³⁺ can promote the transition of Al^[5] and Al^[6] to Al^[4], indicating improvements in the ability of the amorphous material to form Nd³⁺:Y₂O₃–Al₂O₃ vitrified beads, and 1.5 at% Nd³⁺:YAG–Al₂O₃ nanocrystalline transparent ceramics can be obtained by crystallization at 1050 °C with a matrix composed of YAG and concomitant δ-Al₂O₃ and θ-Al₂O₃. The nanocrystalline transparent ceramics show an internal transmittance of 89.56% at 1064 nm, and the strongest emission peak corresponds to the energy transfer from ⁴F_3/2 to ⁴I_11/2 of Nd³⁺ with a fluorescence lifetime of 231 μs when pumped by an 808 nm laser. Specifically, spectral broadening begins to occur, indicating the onset of concentration quenching, when the concentration of Nd³⁺ exceeds 1.5 at%, substantially higher than the 1.0 at% observed in YAG ceramics. YAG–Al₂O₃ nanocrystalline transparent ceramics obtained by amorphous crystallization can be utilized as the matrix to increase the inflexion point of doping concentration quenching of Nd³⁺, and this material may have great potential as a laser gain medium.