Spectroscopic properties of Ho³⁺ ions in biaxial Lu ₂SiO₅ crystal

A high optical quality Ho³⁺-doped lutetium orthosilicate laser crystal Lu₂SiO₅ has been grown by the Czochraski method and the accurate concentration of Ho³⁺ ions in the crystal was measured. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Ho³⁺ ions in the Lu₂SiO ₅ crystal were measured at room temperature. Based on the Judd-Ofelt model, three effective intensity parameters were determined as: Ω_2,eff = 4.57 × 10 ²⁰cm², Ω_4,eff = 3.11 × 10 ²⁰cm², Ω_6,eff = 1.42 × 10²⁰ cm². The fluorescence lifetime of the ⁵I₇ manifold for Ho ³⁺ ions was measured to be 3.3 ms and the quantum efficiency was estimated. The polarized emission cross-sections for the ⁵I ₇ → ⁵I₈ transition were determined by Fuchtbauer-Ladenburg formula. The good spectroscopic properties imply that Ho: Lu₂SiO₅ crystal is a potential laser gain medium for 2 μm lasers.