Spectroscopic investigation of the visible and mid-infrared emission in Tm- and Ho-doped YAG and YLF crystals

Visible and infrared emission spectra of Tm- and Ho-doped YAG and YLF crystals at room temperature, excited with laser radiation at approximately 800 nm, are presented and discussed. The emission intensity dependence on excitation power was measured for each observed spectral band. A comparison of the spectra of these crystals with those of crystals singly-doped with Tm was also performed allowing the identification of the transitions responsible for the emissions and to put forward hypotheses on the de-excitation mechanisms. A quantitative evaluation of the contributions of the separate spectral bands to the total emission was also performed, and this enables to draw a number of conclusions regarding the relative importance of the radiative de-excitation processes. Finally, the experimental results were used in a rate-equation model to obtain a comprehensive picture of the major loss processes in these crystals.