Infrared emission characteristics research of Er3+ and Pr3+ ions doped YSAG single crystal fibers

This study demonstrates that a yttrium aluminum garnet (Y₃Sc₂Al₃O₁₂, YSAG) single crystal fiber (SCF) doped with a specific concentration of Er³⁺ ions and varying concentrations of Pr³⁺ ions was successfully fabricated using the micro-pull-down technique. The fiber produced has a diameter of 3 mm. In this study, the physical and optical properties of the material were studied, conducting a comprehensive X-ray diffraction (XRD) analysis to confirm that the material exhibits a pure phase I_a-3d space group characteristic of YSAG. Subsequently, the thermal expansion behavior of the single crystal fiber was investigated at various doping levels. While the overall trends remained consistent, the specific thermal expansion coefficients and curve gradients exhibited variations among YSAG single crystal fibers with differing dopant concentrations. For the ⁴I_11/2 → ⁴I_13/2 radiation transition of Er³⁺ ions, the peak absorption cross section and peak emission cross section of 0.01 mol% Pr³⁺ ions doped YSAG SCFs are measured to be 6.44 × 10⁻¹⁹ cm² and 6.04 × 10⁻¹⁹ cm², respectively. The peak absorption and emission cross sections of 0.05 mol% Pr³⁺ ions doped YSAG SCFs are measured to be 9.26 × 10⁻¹⁹ cm² and 8.09 × 10⁻¹⁹ cm², respectively. These values represent the highest absorption and emission cross sections obtained in this study. Additionally, the fluorescence lifetimes indicate that at a doping concentration of 0.5 mol% of Pr³⁺ ions, the lifetime difference between the upper and lower energy levels of the 2.7 μm laser is merely 0.09 ms. This observation suggests that Pr³⁺ ions act as an efficient quenching agent within the YSAG SCFs matrix. In the Er³⁺, x mol% Pr³⁺: YSAG (x = 0.01, 0.05, 0.1, 0.3, 0.5) SCFs series, doping with only 0.05 mol% Pr³⁺ ions significantly reduces the fluorescence lifetime difference between the two levels of Er³⁺ ions at the 2.7 μm laser transition from 1.41 ms (in the absence of Pr³⁺ ions) to 0.55 ms. This study provides both a theoretical foundation and empirical data that support the application of Er³⁺, Pr³⁺: YSAG SCFs in laser technology and optical communication.