@article{CHEN2025, 
author = {Yuxuan CHEN and Xin JIANG and Hui SHEN and Tian TIAN and Zefeng JIANG and Jiayue XU},
title = {Growth and Spectra of 6-inch YSZ:Er Crystals},
year = {2025},
journal = {Journal of the Chinese Ceramic Society},
volume = {53},
number = {12},
pages = {3476-3483},
keywords = {yttria-stabilized zirconia, skull melting method, crystal growth, laser crystal},
url = {https://www.sciopen.com/article/10.14062/j.issn.0454-5648.20250442},
doi = {10.14062/j.issn.0454-5648.20250442},
abstract = {IntroductionLasers operating within a spectral range of 1.5–1.7 μm are essential for eye-safe applications like laser ranging, lidar, and optical communications, etc.. Nevertheless, conventional laser crystals such as Er:YAG and Er:LuYO3 have limitations in emission cross-sections or attainable crystal dimensions, thereby constraining their utilization in high-power, large-scale laser systems. To address these challenges, the development of novel laser crystals with substantial crystal sizes and high emission cross-sections is thus imperative. Yttria-stabilized zirconia (YSZ) doped with rare-earth ions emerges as a promising candidate due to its disordered crystalline structure that enables a broader wavelength tunability and a reduced thermal loading under resonant pumping conditions. Specifically, erbium (Er3+) doped YSZ crystals have a significant potential due to its intense emission at 1.5 μm (4I13/2→4F15/2 transition) for eye-safe laser. This study was to investigate the growth of large-scale Er3+-doped YSZ crystals by a skull melting technique, and the optical and spectral properties were systematically investigated to explore a novel laser gain medium in the infra-red region.MethodsPure YSZ and Er3+-doped YSZ crystals (i.e., 0.36%, 1.60% and 2.54% in mole) were grown by a skull melting method (or a cold crucible technique), and a radio frequency (RF) generator was used to heat up the charges. A large-scale furnace with a diameter of approximately 150 cm was employed to accommodate the spontaneous nucleation. Graphite electrodes were used for initial arcing due to the poor conductivity of ZrO2 at < 1200 ℃. At >1200 ℃, raw materials became an electric conductor to form the melting pool. The lowering mechanism started to work at a lowering rate of 2 mm/h, and the melt crystallized from the bottom to the top. After the growth, annealing process was performed to release the internal stresses. The phase and crystal structures of as-grown crystals were characterized by X-ray diffraction (XRD). The transmittance and absorption properties were analyzed by UV–Vis–NIR spectroscopy. The luminescence and decay curve were also systematically evaluated.Results and DiscussionThe results show that Large-sized YSZ and Er-doped YSZ crystals with the diameters and lengths of exceeding 150 mm (6 inches) are grown, representing the largest YSZ single crystals reported. The XRD patterns indicate the cubic structure with a preferred <111>preferred orientation. The lattice parameters increase slightly with Er3+ concentration, indicating the effective incorporation of Er3+ into the YSZ lattice. The transmission of exceeding 74% in the range of 400–1650 nm occurs for pure YSZ crystals, confirming relatively high crystalline qualities. The absorption spectra for Er-doped crystals show some characteristic peaks at 378, 408, 451, 489, 518, 546, 654, 971, 1460 nm and 1530 nm, corresponding to Er3+ transitions from the ground state 4F15/2 to excited states such as 4G11/2 and 4F11/2. The most intense absorption band occurs at 971 nm, which is attributed to the 4F15/2→4F11/2 transition. Under 971 nm excitation, the emission spectra exhibit a dominant peak at 1530 nm for the 4I13/2→4F15/2 transition, which is ideal for eye-safe lasers. The great emission intensity appears at an Er3+ mole concentration of 1.60%, with an emission cross-section of 4.811×10–20 cm2, which is significantly higher than that of Er:YAG (i.e., 0.6×10–20 cm2) and Er:LuYO3 (i.e., 0.261×10–20 cm2). Correspondingly, the decay time of YSZ: 0.36, YSZ: 1.60and YSZ: 2.54 crystals is 1.836 ms, 1.149 ms and 0.797 ms, respectively.ConclusionsThis study demonstrated the effective growth of large-scale (6-inch) YSZ and Er-doped YSZ crystals by a skull melting method. YSZ: Er crystals exhibited an intense emission at 1530 nm under 971 nm excitation. In particular, a high emission cross-section of 4.811×10–20 cm2 and suitable fluorescence lifetime of 1.149 ms appeared for Er3+ of 1.60% in mole. YSZ:Er crystals could be used as a highly promising gain medium for high-power, eye-safe lasers at 1.5 μm due to the ultra-large crystal size and relatively large emission cross-section.}
}