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 mu m related to the I-4(11/2) -> I-4(13/2) Er3+ transition. The peak stimulated-emission cross-section at the expected laser wavelength was calculated to be 0.88x10(-20) cm(2) at 2809 nm for pi-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 I-4(13/2) and I-4(11/2) manifolds amounted to 5.54 ms and 2.66 ms, respectively.