Temperature dependence of the gain in Y3Al5O12:Cr3+:Tm3+:Ho3+

A study was made of the influence of the coactivator concentration on the temperature dependence of the gain due to the ⁵I₇–⁵I₈ transition in the Ho³⁺ ion (λ_l ≈ 2.09 μm) in Y₃Al₅O₁₂:Cr³⁺:Tm³⁺:Ho³⁺ crystals. It was found that the temperature-activated process of loss of the inversion involved the summation of excitations of the upper active level and the ³F₄ level of Tm³⁺. Direct measurements showed that a strong interaction occurred between the ³F₄ (Tm) and ⁵I₇ (Ho) states.