Factors Controlling Infrared-Pumped Visible Emission of Yb3+–Er3+ in the Scheelites

Abstract

The rate equations for green fluorescence of the Yb³⁺–Er³⁺ doubly doped quantum counter are solved for the case of an infrared pump at the Yb^{3+ 2}F_7/2−²F_5/2 transition. The successive transfer of excitation from two Yb³⁺ ions to the Er³⁺ produces green emission from the Er^{3+ 4}S_3/2 level. The increase of the ⁴S_3/2 lifetime with increasing Yb³⁺ concentration in Na_0.5(Y, Yb, Er)_0.5WO₄ confirms the consecutive transfer model of Auzel. Emission from Er³⁺ in a solid solution of divalent cation tungstates or molybdates (having the scheelite structure) under long‐wave ultraviolet excitation is proportional to the inverse of the cation‐anion separation, and hence the binding energy. The emission under infrared excitation is relatively independent of this separation.