From optical spectroscopy to a concentration quenching model and a theoretical approach to laser optimization for Yb3+-doped YLiF4 crystals

A spectroscopic characterization was carried out to identify crystal-field levels for magnetic-dipole transitions of Yb³⁺ ions located in the Y³⁺ dodecahedral S₄ crystallographic site in YLiF₄ (YLF) crystals which were grown either by the Czochralski technique or by the laser heated pedestal growth (LHPG) technique. The concentration dependence of the measured decay time of the ²F_5/2 excited level of Yb³⁺ was analysed in order to understand relevant concentration quenching mechanisms. Under Yb³⁺ ion infrared pumping, self-trapping and up-conversion non-radiative energy transfer to trace rare-earth impurities (Er³⁺, Tm³⁺) has been observed over the visible region and interpreted by a limited-diffusion process within the Yb³⁺ doping ion subsystem to the impurities. The principal parameters useful for a theoretical approach for potential laser applications of Yb³⁺-doped YLiF₄ crystals have also been given.