Quantum efficiency of the down-conversion process in Bi3+-Yb3+ co-doped Gd2O3

In order to evaluate the quantum efficiency of the cooperative energy transfer (CET) process in the Bi3+-Yb3+ co-doped Gd2O3 phosphor, direct measurements of external quantum yield (QY) were performed along with studies of photoluminescence (PL), photoluminescence excitation (PLE) and photoluminescence decay kinetics. The absolute QY measurements reveal considerable discrepancy between the measured quantum efficiencies of the UV to near-IR down-conversion process and the efficiencies estimated from the shortening of the Bi3+ luminescence decay time. The conversion ratio (which should be 2.0 for an ideal quantum cutting mechanism) was found to be less than 1.0 in the studied material.