Erbium-doped materials have important applications in lasers, optical oscillators and optical amplifiers. Cerium trifluoride (CeF₃) crystal is a promising laser host material because of its large rare earth ion radius, high transmittance and low phonon energy, which is helpful to reduce the probability of radiation-free transition. In addition, CeF₃ crystal is an important magneto-optical (MO) material, and has potential applications in polarization switch, MO isolator, Faraday rotator, etc.
Recently, researchers from laser crystal research team of Micro/Nano Optoelectronic Functional Materials Laboratory, Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS) made new progress in rare earth fluoride crystal materials. The findings were published in the Journal of Alloys and Compounds on November 28, 2021.
Based on the CeF₃ crystal, the growth, spectral and MO properties of Er:CeF₃ crystal have been studied. The spectra results show that Er:CeF₃ crystal is beneficial to the output of ~1.5 μm laser, the emission cross section at 1564.6 nm is 1.053×10-20 cm², and the corresponding fluorescence lifetime is 1.675 ms. In addition, the MO analysis shows that Er³⁺ can effectively improve the MO Verdet constants of CeF₃ crystals. The Verdet constants of Er:CeF₃ crystal at 532 nm and 1310 nm are 231.0 rad/(T·m) and 24.4 rad/(T·m), respectively, which are 23.5% and 12.4% higher than those of pure CeF₃ crystal, and also higher than commercial TGG crystal. This improved MO performance is correlated to the doping of Er³⁺ due to the quantum-based super-exchange interaction between Er³⁺ and Ce³⁺. On the other hand, the verdet constant can also be improved by the electric dipole transition caused by the splitting of crystal field level after the doping of rare earth ions. This research provides an important reference for the future exploration of multifunctional crystals with both laser and MO properties.
The research was supported by the National Natural Science Foundation of China and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.

Fig. 1. Fluorescence emission spectrum (a) and the Verdet constant dispersion (b) of Er:CeF3 crystal. (Image by SIOM)

Article website:
https://doi.org/10.1016/j.jallcom.2021.162994