RADIATIVE ENERGY TRANSFER AND "NON-NATURAL" EXCITATION IN THE QUANTUM EFFICIENCY DETERMINATION OF 1.55 µm Er³⁺ EMISSION IN SILICA FIBERS

Abstract
One of the most usual way to determine quantum efficiency of Rare Earth ions in solids is to compute the radiative lifetime (τ_o) of the considered level through Judd's theory and to measure the emission decay time (τ) ; the ratio τ/τ_o being the desired quantum efficiency. By such way the quantum efficiency of Er³⁺ at 1.55 µm in silica fibers is estimated to be 100% [1]. However a number of pitfalls can be encountered [2] in such determination, namely radiative energy transfer and "non-natural" excitation linked with crystal field splittings. The purpose of this paper is to show that, taking such effects into account, Er³⁺ efficiency at 1.55 µm is found to be much less in silica fiber than usually accepted. We show that quantum efficiency of Er³⁺ in silica fibers should range between 30 to 45% instead of the 100% usually believed.