Growth and Spectroscopic Comparison of Monoclinic Er³⁺:GdPO₄ and Tetragonal Er³⁺:YPO₄ Crystals for 1.55 μm Laser Application

Using the top-seeded flux method, monoclinic Er3+:GdPO4 and tetragonal Er3+:YPO4 crystals were grown. Polarized spectral properties of these two crystals with different structures were investigated at room temperature and compared. Peak absorption cross sections of the Er3+:GdPO4 crystal for E//Y polarization and Er3+:YPO4 crystal for π polarization are 1.02 × 10–20 cm2 at 1525 nm and 4.11 × 10–20 cm2 at 1506 nm, respectively. Peak emission cross sections of the Er3+:GdPO4 crystal for E//Y polarization and Er3+:YPO4 crystal for π polarization are 0.88 × 10–20 cm2 at 1525 nm and 2.28 × 10–20 cm2 at 1506 nm, respectively. For the 4I13/2 multiplet of the Er3+:GdPO4 and Er3+:YPO4 crystals, the fluorescence lifetimes are 5.32 and 4.49 ms, and the fluorescence quantum efficiencies are 81 and 95%, respectively. The full widths at half-maximum of the gain spectra of the Er3+:GdPO4 crystal for E//Z polarization and Er3+:YPO4 crystal for π polarization are 60 and 8 nm, respectively, when the inversion parameter is 0.5. Experimental results indicate that the Er3+:YPO4 crystal is a good gain medium of the highly efficient, high-power, and low-threshold 1.55 μm laser, while the Er3+:GdPO4 crystal is a promising gain medium used in broadband tunable and ultrashort pulse 1.55 μm lasers.