Limits of emission quantum yield determination.

In this work we show that comparative experimental methods that evaluate quantities in the form Z/(X-Y) can be heavily biased when Y approaches X. One of such quantities is the photoluminescence quantum yield (QY), given by the ratio of the number of emitted and absorbed photons, where the latter is commonly determined by subtraction of the signal that is transmitted by the sample and by a blank reference. We show that when the measurement uncertainty is larger than 10% of the absorption of the sample, such a comparative method can yield underestimated QY values by more than 200%. We demonstrate this effect in great detail by simulating of the QY methodology that implements an integrating sphere, which is widely used commercially and for research. Based on our simulations, we show that this effect arises from the non-linear propagation of the measurement uncertainties and we quantify the range in which it can be avoided.