Spectroscopy of erbium-doped LiYF4 crystalline layers grown by liquid phase epitaxy

We report on a detailed spectroscopic study of heavily Er³⁺-doped LiYF₄ epitaxial layers with the goal of developing mid-infrared waveguide lasers. Layers with a doping level up to 11 at.% Er³⁺ were grown on (001) oriented undoped bulk LiYF4 substrates using LiF as a solvent. The absorption spectrum of Er³⁺ ions was measured. Under excitation at 973 nm, the layers exhibited intense and strongly polarized mid-infrared luminescence spanning from 2.65 to 2.90 μm related to the ⁴I11/2 → ⁴I13/2 Er³⁺ transition. The peak stimulated-emission cross-section at the expected laser wavelength was calculated to be 0.88×10⁻²⁰ cm² at 2809 nm for π-polarization. By means of low-temperature (12 K) spectroscopy, the experimental crystal-field splitting of Er³⁺ multiplets was determined. The luminescence dynamics from Er³⁺ excited states were studied. For the 11 at.% Er³⁺ doping, the luminescence lifetimes of the ⁴I13/2 and ⁴I11/2 manifolds amounted to 5.54 ms and 2.66 ms, respectively.